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The Evidence for ALS as a Multisystems Disorder of Limited Phenotypic Expression

Michael J. Strong

Abstract: Traditionally, amyotrophic lateral sclerosis (ALS) is considered to be a unique neurodegeneration disorder in which motor neurons are selectively vulnerable to a single disease process. Our current understanding of ALS, however, suggests that this is far too limited an approach. While motor neuron degeneration remains the central component to this process, there is considerable phenotypic variability including broad ranges in survivorship and the presence or absence of cognitive impairment. The number of familial variants of ALS for which unique genetic linkage has been identified is increasing, attesting further to the biological heterogeneity of the disorder. At the cellular level, derangements in cytoskeletal protein and glutamate metabolism, mitochondrial function, and in glial interactions are clearly evident. When considered in this fashion, ALS can be justifiably considered a disorder of multiple biological processes sharing in common the degeneration of motor neurons.

Résumé: Observations indiquant que la SLA est une maladie multisystémique à expression phénotypique limitée. Traditionnellement, la SLA était considérée comme une maladie neurodégénérative dans laquelle les motoneurones sont vulnérables de façon sélective à un processus pathologique unique. Notre compréhension actuelle de la SLA suggère cependant que cette approche est beaucoup trop étroite. Bien que la dégénérescence des motoneurones demeure l'élément central de ce processus, il existe une variabilité phénotypique considérable particulièrement quant à la survie et à la présence ou à l'absence de déficit cognitif. Le nombre de variantes familiales de la SLA pour lesquelles une liaison génétique a été identifiée augmente, attestant de l'hétérogénéité biologique de la maladie. Au niveau cellulaire, il existe des perturbations de la protéine cytosquelettique et du métabolisme du glutamate, de la fonction mitochondriale et des interactions gliales. Quand on regarde la SLA sous cet aspect, on peut à juste titre la considérer comme une maladie due à des processus biologiques multiples ayant en commun la dégénérescence de motoneurones.

Can. J. Neurol. Sci. 2001; 28: 285-298


In spite of the passage of over 100 years since the initial clinicopathological description of amyotrophic lateral sclerosis (ALS), our ability to treat this devastating disease remains limited.1 However, significant gains in our understanding of the pathogenesis of ALS have been achieved, leading to a renewed optimism that efficacious therapies will become available. This article will review our current understanding of the clinical and neurobiological features of ALS, how this relates to a potential understanding of its pathogenesis, and illustrate how this new knowledge has led to the concept of ALS as a clinical and biological disorder affecting multiple aspects of the central nervous system. Approaching ALS in this fashion, not as a unique disease process but rather as the limited phenotypic reflection of a broad spectrum of biological processes, has become integral to our understanding of its potential pharmacotherapy.

New concepts in clinical phenomenology

Increasing age-related mortality rates

With increasing incidence rates with age, ALS is amongst the three major neurodegenerative diseases of our aging population. Alzheimer's disease and Parkinson's disease complete the triad. Although juvenile and early adult onset cases are recognized, these are either uncommon or restricted to specific geographic foci (e.g., juvenile onset ALS in Tunisia).2 In North America, as with most developed countries, the fact that the majority of ALS cases will arise from the older aged segment of the population is of economic significance given the aging of the "baby boomers", of which 75 million were born between 1945 and 1964. For instance, in 1996, 12.7% of the American population was greater than 65 years in age. By 2020, this is anticipated to be 18.0%. Of these patients, the "old old" will rise to 7.0 million from 3.7 million.3 Because of this effect of aging of the population, increasing numbers of ALS patients can be anticipated.

However, age-adjusted mortality rates are even now increasing at a rate disproportionate to that predicted on the basis of societal aging alone.4,5 Age-adjusted mortality rates for ALS in the USA significantly increased in the aged population in the interval from 1977 to 1986, an interval too short to be accounted for solely on the basis of the aging of the population.6 Similar findings of an increased incidence of ALS, particularly amongst the elderly, are evident in Sweden,7,8 Israel,9 the United Kingdom10 and Canada.11 The most parsimonious interpretation of these epidemiological observations is that an environmental factor, acting cumulatively, must contribute to the pathogenesis of ALS.12 Although such a concept must seem intuitive, identifying such factors has proven difficult.

The strongest evidence for an environmental trigger in the induction of motor neuron degeneration has been that of the previously hyper-endemic focus of ALS in the Western Pacific. In this geographically unique region, westernization of the diet of the native peoples is held to have been sufficient to correct chronic nutritional deficiencies of calcium and magnesium, reversing the chronic exposure to a readily bioavailable form of aluminum.13,14 When exposed to a similar calcium-deficient, aluminum supplemented diet, nonhuman primates were found to develop a motor neuron disorder bearing many of the features of ALS.15

For the more common sporadic variants of ALS, only geographic (rural or farming exposure) and industrial (antecedent electrical injury or plastics exposure) factors are associated with disease. While we tend to think of ALS as being in part related to industrialization, farmers and shepherds in Sardinia are amongst those with the highest incidence rates.16

Variability survivorship

Survival curves in ALS are skewed with a broad survival range from months to decades of survival following symptom onset. Long-term survival is not as uncommon as originally thought, with the age at symptom onset and gender being amongst the most important predictors of prolonged survival, irrespective of whether the variant of ALS under consideration is sporadic or familial.17-19 The magnitude of this effect can be readily seen in the patient population of southwestern Ontario in whom symptom onset at less than the age of 45 is associated with a median survival of 54.8 months (40.5, 66.2 months; 25th and 75th percentile, respectively) in contrast to a median survival of 25.4 months with symptom onset after age 45 (9.9, 37.8 months; 25th and 75th percentile, respectively) (p < 0.001). This age-dependency effect is most clearly evident in males, who enjoy a significantly better survivorship associated with a younger age of symptom onset. The gender discrepancy between males and females is lost with increasing age. Although less robust, the site of symptom onset also predicts survival patterns in that amongst all groups, limb onset survival exceeds that of bulbar onsetting disease. On the whole, young males with hand onset of symptoms are amongst the most likely to enjoy long-term survivorship. Whether each of these factors (age and site of symptom onset; gender) simply influences the phenotypic expression of a common disease process, or whether truly biologically discrete processes give rise to each clinical phenotype remains a critical biological question in ALS. It is hard to imagine, however, that the fundamental disease process of a young woman with a malignant disease course is biologically identical to that of a similarly aged male who will likely enjoy a prolonged survival.

Cognitive dysfunction in ALS

Amongst the most convincing arguments in support of ALS as a multisystems disorder has been the recognition of cognitive dysfunction as an integral component of the disease process. The occurrence of cognitive impairment or dementia has been previously considered to be either rare or extremely uncommon in ALS.20 Although the exact prevalence is not known, cognitive impairment will be evident in approximately a third of all patients when carefully assessed.21 Deficits are primarily those of frontal and temporal functions, including mental flexibility, verbal and nonverbal fluency, abstract reasoning and in memory for both verbal and visual material.22-26 Although instances of dementia antedating the onset of amyotrophy are well-recognized,27 and can even manifest as the Klüver Bucy syndrome,28 more often the findings are subtle.29 We observed that individuals with bulbar onsetting disease were more likely to demonstrate cognitive impairment.30 In addition to the features described above, we also found deficits in working memory and problem solving ability - consistent with a frontal temporal lobar degeneration.

Although not evident in all cognitively impaired ALS patients, both static and dynamic neuroimaging studies support the clinical impression of frontal and temporal lobar degeneration, including atrophy on CT scanning and increased T2 signal on MR imaging in both frontal and temporal white matter.22,31,32 These findings are complementary to observations of reduced blood flow in both frontal and temporal neocortices using functional imaging modalities such as SPECT employing either 123I-Imp (123I-N-isopropyl-p-iodoamphetamine) or [99mTc]-d,l-HMPAO.33-36 In the presence of cognitive impairment, reduced rCBF in the anterior cerebral hemispheres and the anterior cingulate gyrus is evident with PET scanning.22,37,38 Defining this further, Abrahams and colleagues39,40 have utilized verbal fluency/word generation tasks for functional PET and observed reduced metabolism in the right dorsolateral prefrontal cortex and left middle and superior temporal gyrus. We observed a significant reduction in the NAA/Cr ratio with MR 1H spectroscopy (consistent with neuronal loss) of the left anterior cingulate gyrus at the earliest time interval studied in those patients developing cognitive impairment.30

The neuropathological correlates of this process include frontal lobar atrophy (Figure 1A), a marked neuronal loss accompanied by spongiform changes in the 2nd and 3rd cortical layers of the frontal lobes and precentral gyrus (Figure 1 B & C) with intraneuronal inclusions in a number of neuronal populations not traditionally thought to be involved in ALS. Using immunohistochemical markers, these inclusions are seen to be unique to ALS and are ubiquitin immunoreactive intraneuronal aggregates assuming either a discrete Lewy body-like morphology or a more amorphous perinuclear arcuate shape. Unlike the aggregates of nonALS patients with a frontotemporal dementia, these inclusions are not immunoreactive for either the microtubule-associated protein tau or for a-synuclein.41-44

It does not appear, however, that the presence of cognitive impairment is an all or nothing phenomenon in ALS. Rather than a strict correlation with the presence or absence of neuropathological changes described above, we have observed that cognitive impairment in ALS appears to best correlate with the extent and load of ubiquitin-immunoreactive intraneuronal aggregates and dystrophic neurites in the frontal and temporal lobes.45 Our findings suggest that there is a continuum of neuropathological change in which neuronal ubiquitin positive aggregates are present in both cognitively intact and cognitively impaired ALS patients but with a greater total load in the latter. Only the presence or absence of superficial linear spongiosus affecting the layers I and II of the frontal cortex clearly discriminated between the two (Figure 1 B & D). This finding of superficial linear spongiosus is a frequently observed finding of the frontal temporal lobar degenerations.46-48

The concept of a continuum of nonmotor neuronal involvement in ALS is also supported by the neuropathological analysis of ventilator dependant ALS patients in whom long-term survival is attained, and in whom neuronal loss and spongiform degeneration of layer II of the frontal cortex is observed.49-52

The above findings are of particular interest in that they provide convincing evidence that ALS is not a disease purely of motor neurons. There is clearly a subset of nonmotor neurons that can become integrally involved in the disease process. The recent observation of genetic linkage of cognitive impairment in familial ALS (fALS) to chromosome 9q21-22 suggests that such a process may also be under the control of specific modifier genes.53 This latter process is distinct from the uncommon chromosome 17 linked disinhibition-parkinsonism-amyotrophy syndrome.54

Familial variants of ALS (fALS)

Although accounting for <10% of ALS cases, advances in our understanding of fALS have provided significant insights into the complexity of the pathogenesis of ALS. While the majority of pedigrees are inherited in an autosomal dominant fashion, autosomal recessive forms are recognized, as are X-linked variants (Table 1). Many inherited variants of motor neuron disease might be best considered as true spinal muscular atrophies, as highlighted by the X-linked spinobulbar atrophy (Kennedy's syndrome) in which corticospinal tract degeneration does not occur. However, others are more clearly variants of ALS in which the triad of bulbar, lower motor neuron and corticospinal tract involvement is evident but with divergent rates of progression or severity.

To highlight the complexity of understanding the genetics of fALS, one need only to examine the striking clinical heterogeneity associated with the most common mutation in fALS. Mutations in the copper/zinc superoxide dismutase (SOD1) gene on chromosome 21 are associated with approximately 15% of the dominantly inherited cases of fALS.55 In spite of extensive studies, the exact mechanism by which alterations in SOD1 directly induce the process of motor neuron degeneration in ALS is still unknown. It has been suggested that these mutations confer a gain of aberrant activity to the SOD1 enzyme, increasing the accessibility of peroxynitrite (ONOO-) to the Cu/Zn binding site and leading to increased rates of reactive nitrating species formation.56,57 Another theory suggests that enhanced rates of hydroxyl radical formation would be catalyzed leading to DNA and membrane damage.58-60 However, the striking variability in both the clinical and neuropathological characteristics of both human pedigrees and transgenic mice harboring mutations in the SOD1 enzyme suggest that the pathogenesis of ALS cannot be attributed solely to aberrant activity of the SOD1 enzyme.61

First, beyond the significant clinical variability associated with the various SOD1 mutations (Table 2), there is significant variability in the neuropathological manifestations amongst the cases of fALS in which SOD1 mutations have been identified. For example, cases expressing the E100G mutation in exon 4 demonstrate features typical of fALS with posterior column involvement but with the additional involvement of both ascending sensory and efferent cerebellar pathways.62 Aggregates of phosphorylated neurofilament are not a significant feature. In contrast, the expression of the I113T mutation in exon 4 is associated with profound neurofilamentous aggregate formation with little ubiquitin immunoreactivity, the absence of posterior column pathology, and the striking finding of tau immunoreactive neurofibrillary tangles in multiple brain stem nuclei.63 The same mutation in another pedigree is associated with marked neurofilamentous aggregate formation restricted to the lower motor neurons.64 fALS cases harboring the A4V mutation manifest with neuropathological features of ALS with posterior column degeneration but, in addition, the unique presence of intracytoplasmic inclusions with intense SOD1 immunoreactivity.65 The A4T mutation in exon 1 is associated with ALS with posterior column involvement without the inclusion formation.66 The most striking example of the extent of phenotypic variability that can occur in a single mutation is observed in families harboring the D90A SOD1 mutation. In these, such divergent manifestations as classical ALS, segmental spinal muscular atrophy, spinal muscular atrophy, or variants of Charcot-Marie-Tooth disease have been observed.67,68 Hence, there is a sufficiently high degree of variability in the neuropathological manifestations of human pedigrees bearing fALS SOD1 mutations to question whether the mutated enzyme, acting alone, is sufficient to induce the disease process.

These human observations are paralleled in transgenic mice expressing SOD1 mutations in which the neuropathological and clinical manifestations vary markedly with the specific SOD1 mutation. Although the initial G93A constructs developed motor dysfunction accompanied by pronounced vacuolar degeneration within motor neurons in the absence of neurofilamentous inclusion formation, the subsequent generation of the G93A mutants developed cytoskeletal pathology reminiscent of ALS.69,70 G85R constructs developed a profound astrocytic pathology consisting of SOD1 and ubiquitin immunoreactive inclusions.71 It is likely, therefore, that specific modifying genes, as yet unknown, are of importance to the ultimate disease phentoype.

Absolute changes in the level of SOD1 activity also cannot explain the induction of motor neuron pathology. While increased levels of SOD1 mRNA have been reported in motor neurons of sporadic ALS (sALS),72 reduced red blood cell SOD1 activity has been documented in heterozygotes for the SOD1 mutation.73 Also, while the down-regulation of SOD1 activity in PC12 cells is associated with apoptotic cell death,74 both the A4V and G37R mutants, when transfected into yeast lacking SOD1, are associated with increased rates of apoptosis.75 Moreover, SOD1 knockout mice fail to develop motor neuron disease.76

Hence, if alterations in the expression of SOD1 are integral to the development of motor system degeneration, this cannot be the only determinant of the disease expression. This concept is supported by the studies of Cleveland and colleagues in which SOD1G85R mice mated with either wild-type SOD1 knockouts or transgenics expressing 6-fold elevated levels of SOD1 failed to modify the extent of clinical or neuropathological disease progression.77 Recalling also that ALS is a chronic neurodegenerative disease with age-dependant incidence rates, little is known of chronic low-level SOD1 mediated neurotoxicity or the effect of age-dependant oxidative damage to the SOD1 enzyme itself.78 In beginning to address this, Cleveland and colleagues have recently observed chronic caspase 1 activation associated with mutant SOD1 expression in vitro, culminating ultimately in apoptotic cell death heralded by caspase 3.79 This novel observation suggests a possible mechanism of the induction of apoptosis in a chronic disease state by the sequential activation of caspases and has been subsequently confirmed in an elegant study utilizing a small peptide caspase inhibitor (zVAD-fmk) in the G93A SOD1 transgenic mice to induce a significant increase in survival.80 It is worth recognizing, however, that whether cell death in ALS is apoptotic remains to be ascertained with certainty.81,82

ALS as a multifactorial disease process

There is little doubt that at the cellular level, ALS can be attributed to a number of discrete biological processes. In the preceding discussion, this is most clearly highlighted by the similarities of ALS phenotype between the fALS and sALS cases, in spite of clearly differing genetic compositions. ALS also affects a number of neuronal metabolic pathways, including such diverse processes as oxidative injury, excitotoxicity, altered cytoskeletal protein homeostasis, a failure of calcium homeostasis and alterations in mitochondrial function. Whether these are truely discrete processes, each of which can serve as an etiological trigger for the disease, or whether they represent integrally related processes as a part of a cascade of neuronal degeneration ultimately culminating in cell death, remains to be determined. Intuitively, the latter would seem the more likely process. While considerable interest has arisen with regards to the nonneuronal biological effects in ALS (e.g., alterations in skin glycosaminoglycans83), this review will focus on the neurobiological aspects of the pathogenesis of ALS.


The neuropathological diagnosis of ALS is established by the finding of widespread motor neuron selective degeneration in a topographically specific pattern that includes a loss of specific motor neuron pools with chromatolytic neurons, degeneration of descending innervation pathways and atrophy of ventral spinal roots.84 In familial variants of the illness, pallor of the spinocerebellar tracts and posterior columns with degeneration of Clarke's nucleus may also be observed.85 As discussed above, this concept at minimum must now be modified to incorporate an understanding of the nonmotor neuronal degeneration that forms the basis of cognitive impairment in a population of ALS patients.

The ultrastructural hallmark of ALS is an accumulation of neurofilamentous material within degenerating neuronal perikaryal and axonal processes, the deposition of ubiquitin-conjugated material, and the immunohistochemical evidence of oxidative damage86-89 (Figure 2). The neurofilamentous aggregates consist of masses of interwoven skeins of neurofilamentous material, appearing either as Lewy body-like inclusions, or amorphous aggregates infiltrating the perikaryon and extending into neuritic structures. Such aggregates are also immunoreactive to antibodies recognizing a internexin, a related intermediate filament.90 In contrast, neuroaxonal aggregates localized to the neuritic process and consisting primarily of neurofilamentous material are immunoreactive for peripherin.91 This suggests that the composition of such aggregates is dependant to some degree on the somatotopic localization of the aggregate within the neuron and the relative contribution of the cytoskeleton to the normal cellular structure at that point.

Immunohistochemical and molecular studies of ALS have provided us with some degree of understanding of the generation of neurofilamentous aggregates in ALS. Amongst neuronal populations, motor neurons possess the greatest axonal lengths and complexity relative to perikaryal size and thus giving rise to the necessity of a high content of neurofilament (NF) proteins.92 These proteins, members of the highly conserved intermediate family of cytoskeletal proteins, are three separate but closely related proteins consisting of a highly conserved a-helical core domain, a N-terminus domain that is integral to the initial assembly process, and a C-terminus domain in which the size is based largely upon the number of multiphosphorylation repeats (KSVP sequences).93 Based on this latter property, NFs are defined on the basis of molecular weight as low molecular weight (NFL), intermediate molecular weight (NFM) or high molecular weight (NFH). Disruption of the assembly of the NF triplet protein, a heteropolymer composed of the initial homopolymerization of the NFL proteins followed by the layering on of the NFM or NFH proteins, results in a motor neuron degeneration.94-97 Altering the stoichiometry of NF expression in transgenic models also results in the formation of neurofilamentous aggregates and a motor neuron degeneration.98-100 Altering the NFL rod domain through a point mutation will sufficiently disrupt NFL homopolymerization to inhibit the triplet protein assembly. As demonstrated by Julien and colleagues,101 double transgenic mice containing a NFL deletion and over expression of peripherin develop a motor neuron degenerative state containing a striking number of parallels to ALS.

Perhaps the most convincing evidence to date that alterations in NF biochemistry can be integral to ALS include the demonstration by Bergeron and colleagues of selective suppressions of NFL mRNA steady state levels in degenerating ALS motor neurons102 and our demonstration that this alters the stoichiometry of NFL, NFM and NFH steady state mRNA levels in a fashion consistent with transgenic mouse models of motor neuron disease.90

Secondly, motor neurons are rich sources of free oxygen radicals, nitric oxide synthase and SOD1. The presence of free oxygen radicals and nitric oxide leads to the formation of peroxynitrite which, in the presence of SOD1, can be catalyzed to form reactive nitrating species. Reactive nitrating species will preferentially modify phenolic residues (e.g., tyrosine residues), of which NFL is an abundant source. The nitration of NFL as the end result of SOD1 mediated catalysis of peroxynitrite has thus been proposed as a mechanism in the pathogenesis of ALS, and indeed, when NFL is nitrated and then added to an otherwise intact NF isolate containing NFL, NFM and NFH, the NF triplet assembly is inhibited.103 All the key constituents necessary to drive this reaction have been observed in ALS motor neurons, including the constitutive expression of the neuronal isoform of NOS,104 the byproducts of nitric oxide synthesis,105 an abundance of both SOD1 mRNA106 and enzyme107,108 and intense nitrotyrosine immunoreactivity co-localizing to intracellular aggregates.109 Concentrations of free 3-nitrotyrosine (a specific marker of reactive nitrating species formation) and its metabolite, 3-nitro-4-hydroxyphenol acetic acid as measured by high performance liquid chromatography, are elevated compared to controls.110 Such elevations are reminiscent of those observed in transgenic mice expressing the human SOD1G93A mutation.111 These observations suggest that elevated levels of reactive nitrating species are present in ALS. Further, SOD1 mutations observed in fALS alter the activity of SOD1 to preferentially generate reactive nitrating species and increase nitration of NFL.112

The hypothesis that NFL nitration will give rise to the motor neuron degeneration of ALS thus becomes rather appealing. Unfortunately, neither the role of altered SOD1 activity or of reactive nitrating species in the pathogenesis of ALS is fully understood. When NF isolates were examined from both ALS and age-matched control cases, we found no evidence for a significant alteration in the extent of nitration in ALS NFL.113 Rather, these have led to our proposal that, distinct from its role in NF triplet assembly, NFL may function as a biological sink for reactive nitrating species. In support of this, we have observed in vitro that spinal motor neurons derived from NFL -/- transgenics are more sensitive to the toxicity of reactive nitrating species than are either control or hNFL +/+ cultures.114

The third piece of evidence that alterations in NF homeostasis are of significance in ALS relates to the findings of mutations in the NFH C-terminus domains in a number of sALS cases.115-118 Not every study has replicated these findings.119 These mutations, for the most part, are localized to the MPR regions and would be predicted to alter the phosphorylation state of NFH. Although this represents an absolute minority of ALS cases, these observations serve to highlight that the phosphorylation domains of the NF proteins may be critical to the genesis of ALS. While our recent observation that there are no significant differences in the physicochemical properties of ALS NFH when contrasted to control NFH isolates would seem to argue against this, to date, we know little of the dynamics of NFH phosphorylation and how this is altered in ALS.120

Mitochondrial dysfunction and oxidative stress in ALS

There is considerable evidence of mitochondrial dysfunction in ALS. At the ultrastructural level, this includes the observations of abnormal mitochondrial morphology in motor nerve terminals,121 liver122,123 and muscle.124 Metabolic studies of the central nervous system have found significant reductions in cytochrome oxidase activity,125 increases in either complex I activity alone,126 or both complex I and II.127

Nonneuronal tissue derived from ALS patients also demonstrates abnormalities in mitochondrial function, including ALS derived platelets.128 In ALS derived lymphocytes, increased cytosolic calcium concentration and impaired responses to uncouplers of oxidative phosphorylation suggest impaired mitochondrial function.129

The implications of mitochondrial dysfunction in ALS relate specifically to the consequent increased extent of oxidative damage, including oxidative damage to SOD1 (reduced activity), to neurofilaments (potential of enhanced cross-linking) and for further damage to the mitochondrial energy transfer site with a resultant increase in mitochondrial proton loss and cell death. Mitochondrial damage will also lead to altered calcium homeostasis and through cytochrome C release, increased rates of apoptosis. In concert with mitochondrial damage, the lack of expression of calcium binding proteins (calbindin D-28K, parvalbumin) within specific populations of motor neurons, and hence the ability to buffer calcium, has been suggested to be a determinant of the motor neuron sensitivity observed in ALS.92,130-135 Hence, while there is no evidence that ALS is a mitochondrial cytopathy, there is considerable evidence that mitochondrial dysfunction is of significance.

The net effect of the increased generation of reactive oxygenating species, fueled by abnormalities of the electron transport chain and an increased leakage of oxygen radicals from the damaged mitochondria is compounded by a deficiency of key free radical scavenging enzymes.136,137 As a consequence, increased protein carbonyl formation in both the motor cortex and in the spinal cord has also been observed.59,126,138,139

Excitotoxicity in ALS

Although there remains controversy surrounding the potential mechanisms by which glutamate-mediated excitotoxicity might occur in ALS, there is considerable evidence in both the clinical and experimental literature to implicate glutamate-mediated motor neuron toxicity in ALS.140,141 Glutamate is released into the synaptic cleft when the pre-synaptic terminal is depolarized. It then diffuses across the synaptic cleft to activate the post-synaptic neuron by interacting with either ionotropic (e.g., NMDA, AMPA, or kianate) or metabotropic (G-protein coupled) receptors. Excitatory synaptic transmission is terminated by the rapid uptake of glutamate. Five glutamate transporters have been cloned, including the asctrocyte-specific variant EAAT-2 (GLT-1). Following uptake of glutamate, it is either transaminated to form glutamine or metabolized to a-ketoglutarate; both of which serve as neuronal precursors to glutamate synthesis. Excesses of extracellular glutamate induce neurotoxicity by either increasing neuronal sodium and chloride influx during depolarization, or by an excess of calcium influx. The latter has direct consequences in the activation of a number of calcium-dependant enzymes (i.e., phospholipases, xanthine oxidase, neuronal nitric oxide synthase, etc.) and in inducing DNA damage, lipid peroxidation, and mitochondrial dysfunction.

It was of some interest to then find that a reduction in the glial glutamate transporter GLT-1 and an alteration in the mRNA encoding the astrocytic glutamate transporter, EAAT-2 existed in the majority of sALS cases.142,143 Initially predicted to affect upwards of 80% of sALS patients, this alteration in RNA processing was postulated to give rise to excessive extracellular levels of glutamate, thereby leading to glutamate-mediated cytotoxicity. In subsequent studies, however, it has become less clear that these alterations in RNA processing are specific to ALS.144-146

Regardless, astrocytic proliferation is a key neuropathological feature of ALS and, while likely a response to the induction of motor neuron degeneration, it cannot be ignored. Transgenic mice models expressing fALS mutations have been associated with the initial formation of SOD-immunoreactive aggregates in astrocytes, suggesting that, at least in these models, astrocytic pathology may be a harbinger of subsequent neuronal damage. It is also relevant that the in vivo activation of the AMPA/kainate receptor decreases the expression of NF mRNA and NF phosphorylation,147 both of which are key considerations discussed earlier.

 Microglial activation in ALS

Although it has been generally held that the immune system plays little, if any, role in the pathogenesis of ALS, microglial (CNS resident macrophages) proliferation and activation is a prominent feature of ALS.148-151 In the ventral and lateral funiculi of the spinal cord, microglia assume a phagocytic morphology (foamy macrophages) suggesting a not unexpected response to the corticospinal tract degeneration (Figure 3 A&B). In contrast, activated microglia of the ventral horns are in close approximation to otherwise healthy-appearing motor neurons and do not demonstrate the morphology of phagocytic microglia (Figure 3 C&D). In cognitively impaired ALS patients, microglial activation is a prominent feature accompanying superficial linear spongiosis (Figure 1 C&D). The central question remains as to whether such microglial activation participates directly in the pathogenesis of ALS.

The inter-relationship between injured neurons and microglia is complex. When present in the "resting state", microglia have finely branched processes that extend in multiple directions. In response to a variety of pathological insults, microglia rapidly activate and their processes retract and hypertrophy, resulting in a phagocytic morphology. In concert with this activation, microglia upregulate the expression of a number of cell surface antigens and become active secretory cells. The observation of a prominent perineuronal microglial proliferation and migration within 24 hours of a neuronal injury suggests that injured neurons possess the inherent capacity to induce a microglial response.152,153 Inhibition of this response, for instance in the model of optic nerve transection with inhibition of the intraretinal microglial response with a macrophage inhibitory peptide, is associated with an enhanced rate of optic nerve axon survival and a greater degree of axonal regeneration.154,155 In contrast, induction of the post-axotomy microglial response with a macrophage stimulating factor at the time of axotomy induces a faster rate of ganglion cell degeneration. Similarly, the in vivo inhibition of microglial activation will attenuate neuronal degeneration induced by either ischemia156 or by the excitatory neurotoxin ibotenic acid.157

Microglial neurotoxicity can be mediated through a number of cytotoxic pathways or by phagocytosis. This includes the synthesis of glutamate and other NMDA receptor agonists,158,159 and of toxic superoxide radicals,160 the expression of an inducible form of nitric oxide synthase (iNOS) that renders them a potent source of the nitric oxide, relevant to the earlier discussion of oxidative injury, and the secretion of a number of proteolytic enzymes, active lysosomal proteases and arachidonic acid metabolites - all of which are cytotoxic.161 Microglia can also be neuroprotective, and can inhibit NO-donor (sodium nitroprusside) induced neuronal apoptosis in vitro through a TNF-a dependant mechanism.162

Hence, the critical issue remains the extent to which microglia participate directly in the pathogenesis of ALS. To address this, we have examined the role of microglia in an experimental model of motor neuron degeneration in which clinical and neuropathological recovery is possible and determined that the absence of a microglial response was permissive to recovery.163,164 We have subsequently demonstrated that injured motor neurons release soluble factor(s) that induce microglial activation, and that following activation, these microglia are able to stimulate nitric oxide generation in otherwise healthy motor neurons. These findings suggest that microglial cells can in fact be direct participants in the neurodegenerative process of ALS. In this light, the recent observation of increased interleukin-6 levels in CSF of ALS patients is thus of considerable interest, although earlier studies had failed to observe this.165,166

 Lessons from pharmacotherapeutics

Given the complexity of the biology of ALS described above, it should not be surprising that pharmacologically modifying the course of ALS has been fraught with failure, in spite of the utilization of individual agents with strong theoretical potential to be effective. These include agents potentially designed to inhibit or prevent cell damage (antiglutamatergic or neurotrophic agents, antioxidants, antiviral agents), to enhance neuronal repair (gangliosides), to inhibit immune-mediated damage (immunomodulatory agents) or to enhance neuromuscular function (monoamines or cholinergic agents). With the sole exception of the antiglutamatergic and neurotrophic therapies, there is no evidence of efficacy for the remaining classes of therapy.167

Antiglutamatergic agents

The only antiglutamatergic agent for which a suggestion of efficacy is available is rilutek (Riluzole). Riluzole appears to improve survival but the degree of improvement is small. In the pivotal phase III study, NNT values ranged from 20 to 14 with broad 95% confidence intervals (approaching infinity).168 Riluzole did not appear to slow the rate of decline of patient functional assessments in either of the pivotal studies, although a subsequent retrospective analysis suggested a prolongation of time spent within a less severely affected stage of the illness.169 More recent evidence utilizing proton density magnetic resonance spectroscopy has, however, suggested that patients receiving riluzole demonstrate less neuronal loss in the motor strip and may, in fact, demonstrate an arrest of neuronal loss.170

A number of other antiglutamatergic therapies have been used without success in ALS. These include L-threonine,171 branched chain amino acids,172,173 dextromethorphan,174 gabapentin,175 lamotrigine176 and verapamil.177

 Neurotrophic therapies

There is little evidence that the use of neurotrophic factors has had a significant impact on the rate of progression of ALS, with recombinant human insulin-like growth factor (rhIGF-1) amongst the most promising. However, only one of two valid random controlled trials of rhIGF-I revealed results favouring improvement in mortality, rate of clinical decline, and quality of life in ALS. In the North American trial, NNT to progress less than 20 points on A-ALS scale over nine months using 0.1 mg/day rhIGF-1 sc was six (95%CI = 3-25), and to survive 30 months was eight (95%CI = 4-").178 Ackerman and colleagues concluded that rhIGF-1 was most effective in patients at an earlier stage of disease, or if they possessed a more rapid disease course.179 However, only 53% of patients completed the North American study protocol. In contrast, the European protocol failed to show a significant difference in either measure.180

The list of failed neurotrophic factor therapies in ALS is daunting, and includes ciliary neurotrophic factor,181,182 growth hormone,183 thyrotropin releasing hormone184-187 and, most recently, either subcutaneous or intrathecally administered brain-derived neurotrophic factor (BDNF).

Immunomodulatory therapy

In spite of the apparent role of microglia in the disease process, immunomodulatory therapies have been largely unsuccessful. These have included cyclophosphamide,188-190 cyclophosphamide combined with IvIg191 or with prednisone,190 plasmapheresis alone192 or with azathioprine,193 total lymph node irradiation,194 and cyclosporine.195


A number of failed clinical trials, while limited in scope, have examined a variety of other treatment modalities in ALS. These have included studies of monoamine therapies utilizing deprenyl196-198 or L-dopa.199 Direct attempts at enhancing cholinergic function have also failed, including physostigmine alone200 or in combination with neostigmine,201 3,4-diaminopyridine202 and tetrahydroaminoacridine.203 Antiviral therapies, in spite of the recent interest surrounding polymerase chain reaction evidence of viral DNA fragments in ALS motor neurons, have been ineffective.204,205


Can some semblance of cohesion be brought forward from the above? Clearly, the clinical, neuropathological and neurochemical evidence mandates that ALS no longer be considered to be a discrete disorder of the motor neurons, but rather one in which the manifestation of neuromuscular dysfunction is one of a heightened threshold for the development of dysfunction in motor neurons, but not a selectivity. Understanding this propensity for degeneration within selective populations of motor neurons has thus become paramount in understanding the pathogenesis of ALS, and by corollary, its treatment.

Previously thought to be the sole domain of ALS patients whose survival was artificially prolonged through aggressive respiratory support, alterations in cognition are an integral component of ALS within a defined subpopulation of patients. The lessons from fALS would suggest that the development of cognitive impairment in ALS may be under the control of modifier genes, similar in many ways to the determinants of phenotypic variation or risk in Alzheimer's disease. In sALS, the manifestation of cognitive impairment is not an all or nothing phenomenon, but rather a reflection of the total burden of neuropathological damage. Determining whether this is a ubiquitous phenomenon in sALS will require careful longitudinal cliniconeuropathological studies.

The striking diversity of genetic defects observed in both juvenile and adult variants of fALS also attests to the pathogenetic heterogeneity of ALS, yielding clinical syndromes with little clinical variability. The most poignant argument, however, rests with the mutations in the SOD1 gene in which a single enzyme, mutated by a wide variety of point mutations, yields divergent neuropathological and clinical phenotypes.

Integrating the neuropathological and neurochemical features of ALS is somewhat more challenging, but again, the disorder must be considered to be multifactorial and multisystem. In many senses, it may not be relevant for the majority of individuals whether the nature of the initial triggering event is known. Whatever the trigger, motor neurons appear to be placed at a greater risk for disease, based on their large size and extensive axonal processes requiring an abundance of NF and mitochondria. This is coupled with a lack of key calcium binding proteins (e.g., calbindin D-28K and parvalbumin), a lack of the GluR2 AMPA receptor subunit (enhancing its risk for calcium mediated neurotoxicity) and the high expression of the SOD1 enzyme. By the time the illness is clinically evident, a lethal cascade has been established with the involvement of not only multiple biological intracellular processes (including, but not exclusive to, NF aggregate formation with potential axostasis, mitochondrial damage with increased cytosolic calcium and activation of caspase 1, oxidative injury with DNA damage) but clearly involvement of the adjacent glial cells.

Although the proposed deficiency of glutamate transporter EAAT2 remains to be confirmed, there is considerable evidence to suggest that CSF and tissue glutamate levels are increased in ALS and that this will have a deleterious effect on motor neuron survival. This will be further augmented by the nature of the interaction between microglial cells and motor neurons. Upon injury, motor neurons signal to microglia to induce proliferation, upregulation of activity, and migration. Stimulated microglia are amongst the most potent generators of glutamate in the central nervous system. Failure of glutamate uptake by astrocytes defective in EAAT2 would leave the already vulnerable motor neuron open to excitotoxic injury. The increased influx of calcium induced by such glutamate mediated activation of NMDA receptors will not have a single effect, but rather a cascade of effects that would enhance cellular injury. This includes upregulating nNOS expression and activation, with a consequent increase in nitric oxide generation and the formation of reactive metabolites. We have shown that, in the presence of neurofilament aggregates induced by alterations in NF stoichiometry, motor neurons are at a higher risk for the development of a neurotoxic cell death.114

Finally, the virtually total failure of pharmacotherapeutic agents to impact on ALS progression, in spite of multiple potential sites of effect, strongly suggest that the biological process of ALS is far more complex than anticipated. A parsimonious view of ALS thus should include the intimate nature of the interactions between all of these cell types and the suggestion that once induced, this triumvirate of cells (motor neuron, astrocyte and microglia) is largely responsible for the manifestations of ALS as we recognize them. Pharmacotherapy should thus reflect a similar approach to the triumvirate.


Research supported by the ALS Society of Canada, the American ALS Association (ALSA) and by the Premier's Research Excellence Award.



Charcot JM, Joffroy A. Deux cas d'atrophie musculaire progressive avec lésions de la substance grise et des faisceaux antérolatéraux de la moelle épinière. Arch Physiol Norm Pathol 1869; 2:354-744.


Ben Hamida M, Hentati F, Ben Hamida C. Hereditary motor system diseases (chronic juvenile amyotrophic lateral sclerosis). Brain 1990; 113:347-363.


McDaniel JL, Via BG. Aging issues in the workplace. Assisting workers who provide eldercare. AAOHN J 1997; 45(5):261-269.


Lilienfeld DE, Ehland J, Landrigan PJ, et al. Rising mortality from motoneuron disease in the USA, 1962-84. Lancet 1989; i:710-713.


Durrleman S, Alperovitch A. Increasing trend of ALS in France and elsewhere: are the changes real? Neurology 1989; 39:768-773.


Riggs JE. Longitudinal gompertzian analysis of amyotrophic lateral sclerosis mortality in the U.S., 1977 - 1986: evidence for an inherently susceptible population subset. Mech Ageing Dev 1990; 55:207-220.


Neilson S, Gunnarsson L-G, Robinson I. Rising mortality from motor neurone disease in Sweden 1961 - 1990: the relative role of increased population life expectancy and environmental factors. Acta Neurol Scand 1994; 902:150-159.


Gunnarsson L-G, Lindberg G, Söderfelt B, Axelson O. The mortality of motor neuron disease in Sweden. Arch Neurol 1990; 47:42-46.


Kahana E, Zilber N. Changes in the incidence of amyotrophic lateral sclerosis in Israel. Arch Neurol 1984; 41:157-160.


Buckley J, Warlow C, Smith P, et al. Motor neuron disease in England and Wales, 1959 - 1979. J Neurol Neurosurg Psychiat 1983; 46:197-205.


Hudson AJ, Davenport A, Hader WJ. The incidence of amyotrophic lateral sclerosis in southwestern Ontario, Canada. Neurology 1986; 36:1524-1528.


Strong MJ. Exogenous neurotoxins. In: Brown RH, Jr, Meininger V, Swash M, eds. Amyotrophic Lateral Sclerosis. London: Martin Dunitz Ltd., 2000: 279-287.


Garruto RM. Amyotrophic lateral sclerosis and Parkinsonism-dementia of Guam: clinical, epidemiological and genetic patterns. Am J Human Biol 1989; 1:367-382.


Garruto RM. Pacific paradigms of environmentally-induced neurological disorders: Clinical, epidemiological and molecular perspectives. Neurotoxicology 1991; 12:347-378.


Garruto RM, Shankar SK, Yanagihara R, et al. Low-calcium, high aluminum diet-induced motor neuron pathology in cynomolgus monkeys. Acta Neuropathol 1989; 78:210-219.


Giagheddu M, Puggioni G, Biancu F, et al. Epidemiological study of amyotrophic lateral sclerosis in Sardinia, Italy. Acta Neurol Scand 1983; 68:394-404.


Strong MJ, Hudson AJ, Alvord WG. Familial amyotrophic lateral sclerosis, 1850-1989: a statistical analysis of the world literature. Can J Neurol Sci 1991; 18:45-58.


Eisen A, Schulzer M, MacNeil M, Pant B, Mak E. Duration of amyotrophic lateral sclerosis is age dependent. Muscle Nerve 1993; 16:27-32.


Jablecki CK, Berry C, Leach J. Survival prediction in amyotrophic lateral sclerosis. Muscle Nerve 1989; 12:833-841.


Hudson A. Amyotrophic lateral sclerosis and its association with dementia, parkinsonism and other neurological disorders: a review. Brain 1981; 194:217-247.


Massman PJ, Sims J, Cooke N, et al. Prevalence and correlates of neuropsychological deficits in amyotrophic lateral sclerosis. J Neurol Neurosurg Psychiat 1996; 61:450-455.


Kew JJM, Goldstein LH, Leigh PN, et al. The relationship between abnormalities of cognitive function and cerebral activation in amyotrophic lateral sclerosis. Brain 1993; 116:1399-1423.


David AS, Gillham RA. Neuropsychological study of motor neuron disease. Psychosomatics 1986; 27:441-445.


Iwasaki Y, Kinoshita M, Ikeda K, Takamiya K, Shiojima T. Neuropsychological dysfunctions in amyotrophic lateral sclerosis: relation to motor disabilities. Intern J Neurosci 1990; 54:191-195.


Neary D, Snowden JS, Gustafson L, et al. Frontotemporal lobar degeneration. A consensus on clinical diagnostic criteria. Neurology 1998; 51:1546-1554.


Bak TH, O'Donovan DG, Xuereb JH, Boniface S, Hodges JR. Selective impairment of verb processing associated with pathological changes in Brodmann areas 44 and 45 in the motor neuron disease-dementia-aphasia syndrome. Brain 2001; 124:103-120.


Caselli RJ, Windebank AJ, Petersen RC, et al. Rapidly progressing aphasic dementia and motor neuron disease. Ann Neurol 1993; 33:200-207.


Devinsky O, Morrell MJ, Vogt BA. Contributions of anterior cingulate cortex to behaviour. Brain 1995; 118:279-306.


Strong MJ, Grace GM, Orange JB, Leeper HA. Cognition, language and speech in amyotrophic lateral sclerosis: a review. J Clin Exp Neuropsych 1996; 18(2):291-303.


Strong MJ, Grace GM, Orange JB, et al. A prospective study of cognitive impairment in ALS. Neurology 1999; 53:1665-1670.


Poloni M, Capitani E, Mazzini L, Ceroni M. Neuropsychological measures in amyotrophic lateral sclerosis and their relationship with CT scan-assessed cerebral atrophy. Acta Neurol Scand 1986; 74:257-260.


Gallassi R, Montagna P, Morreale A, et al. Neuropsychological, electroencephalogram and brain computed tomography findings in motor neuron disease. Eur Neurol 1989; 29:115-120.


Ludolph AC, Elger CE, Böttger IW, et al. N-isopropyl-p-123I-amphetamine single photon emission computer tomography in motor neuron disease. Eur Neurol 1989; 29:255-260.


Ohnishi T, Hoshi H, Nagamachi S, et al. Regional cerebral blood flow study with 123I-IMP in patients with degenerative dementia. Am J Neuroradiol 1991; 12:513-520.


Waldemar G, Varstrup S, Jensen TS, Johnsen A, Boysen G. Focal reductions in cerebral blood flow in amyotrophic lateral sclerosis: a [99mTc]-d,l-HMPAO SPECT study. J Neurol Sci 1992; 107:19-28.


Talbot PR, Goulding PJ, Lloyd JJ, et al. Inter-relation between "classic" motor neuron disease and frontotemporal dementia: neuropsychological and single photon emission computed tomography study. J Neurol Neurosurg Psychiat 1995; 58:541-547.


Tanaka M, Kondo S, Hirai S, et al. Cerebral blood flow and oxygen metabolism in progressive dementia associated with amyotrophic lateral sclerosis. J Neurol Sci 1993; 120:22-28.


Ludolph AC, Langen KJ, Regard M, et al. Frontal lobe function in amyotrophic lateral sclerosis: a neuropsychological and positron emission tomography study. Acta Neurol Scand 1992; 85:81-89.


Abrahams S, Leigh PN, Kew JJM, et al. A positron emission tomography study of frontal lobe function (verbal fluency) in amyotrophic lateral sclerosis. J Neurol Sci 1995; 129(Suppl.):44-46.


Abrahams S, Goldstein LH, Lloyd CM, Brooks DJ, Leigh PN. Cognitive deficits in nondemented amyotrophic lateral sclerosis patients: a neuropsychological investigation. J Neurol Sci 1995; 129(Suppl.):54-55.


Mitsuyama Y. Presenile dementia with motor neuron disease in Japan: clinico-pathological review of 26 cases. J Neurol Neurosurg Psychiat 1984; 47:953-959.


Okamoto K, Hirai S, Yamazaki T, Sun X, Nakazato Y. New ubiquitin-positive intraneuronal inclusions in the extra-motor cortices in patients with amyotrophic lateral sclerosis. Neurosci Lett 1991; 129:233-236.


Wightman G, Anderson VER, Martin J, et al. Hippocampal and neocortical ubiquitin-immunoreactive inclusions in amyotrophic lateral sclerosis with dementia. Neurosci Lett 1992; 139:269-274.


Anderson VER, Cairns NJ, Leigh PN. Involvement of the amygdala, dentate and hippocampus in motor neuron disease. J Neurol Sci 1995; 129(Suppl.):75-78.


Wilson CM, Grace GM, Munoz DG, He BP, Strong MJ. Cognitive impairment in sporadic ALS. A pathological continuum underlying a multisystem disorder. Neurology 2001; 57:651-657.


Munoz DG. The pathology of Pick complex. In: Kertesz A, Munoz DG, eds. Pick's disease and Pick complex. New York: John Wiley and Sons, 1998: 211-239.


Jackson M, Lowe J. The new neuropathology of degenerative frontotemporal dementias. Acta Neuropathol 1996; 91:127-134.


Giannakopoulos P, Hof PR, Bouras C. Dementia lacking distinctive histopathology: clinicopathological evaluation of 32 cases. Acta Neuropathol (Berl) 1995; 89:346-355.


Hayashi H, Kato S. Total manifestations of amyotrophic lateral sclerosis. J Neurol Sci 1989; 93:19-35.


Mizutani T, Aki A, Shiozawa R, et al. Development of ophthalmoplegia in amyotrophic lateral sclerosis during long-term use of respirators. J Neurol Sci 1990; 99:311-319.


Hayashi H, Kato S, Kawada A. Amyotrophic lateral sclerosis patients living beyond respiratory failure. J Neurol Sci 1991; 105:73-78.


Kishikawa M, Nakamura T, Iseki M, et al. A long surviving case of amyotrophic lateral sclerosis with atrophy of the frontal lobe: a comparison with the Mitsuyama type. Acta Neuropathol 1995; 89:189-193.


Hosler BA, Siddique T, Sapp PC, et al. Linkage of familial amyotrophic lateral sclerosis with frontotemporal dementia to chromosome 9q21-q22. JAMA 2000; 284(13):1664-1669.


Lynch T, Sano M, Marder KS, et al. Clinical characteristics of a family with chromosome 17-linked disinhibition-dementia-parkinsonism-amyotrophy complex. Neurology 1994; 44:1878-1884.


Rosen DR, Siddique T, Patterson D, et al. Mutations in Cu/Zn superoxide dismutase gene are associated with familial amyotrophic lateral sclerosis. Nature 1993; 362:59-62.


Beckman JS, Carson M, Smith CD, Koppenol WH. ALS, SOD and peroxynitrite. Science 1993; 364:584-584.


Bruijn LI, Beal FM, Becher MW, et al. Elevated free nitrotyrosine levels, but not protein-bound nitrotyrosine or hydroxyl radicals, throughout amyotrophic lateral sclerosis (ALS)-like disease implicate tyrosine nitration as an aberrant in vivo property of one familial ALS-linked superoxide dismutase 1 mutant. Proc Natl Acad Sci USA 1997; 94(14):7606-7611.


Bogdanov MB, Ramos LE, Xu Z, Beal FM. Elevated "hydroxyl radical" generation in vivo in an animal model of amyotrophic lateral sclerosis. J Neurochem 1998; 71:1321-1324.


Ferrante RJ, Browne SE, Shinobu LA, et al. Evidence of increased oxidative damage in both sporadic and familial amyotrophic lateral sclerosis. J Neurochem 1997; 69:2064-2074.


Wiedau-Pazos M, Goto JJ, et al. Altered reactivity of superoxide dismutase in familial amyotrophic lateral sclerosis. Science 1996; 271:515-518.


Tu P-H, Gurney ME, Julien J-P, Lee VMY, Trojanowski JQ. Oxidative stress, mutant SOD1, and neurofilament pathology in transgenic mouse models of human motor neuron disease. Lab Invest 1997; 76(4):441-456.


Ince PG, Shaw PJ, Slade JY, Jones C, Hudgson P. Familial amyotrophic lateral sclerosis with a mutation in exon 4 of the Cu/Zn superoxide dismutase gene: pathological and immunocytochemical changes. Acta Neuropathol 1996; 92:395-403.


Orrell RW, King AW, Hilton DA, et al. Familial amyotrophic lateral sclerosis with a point mutation of SOD-1: intrafamilial heterogeneity of disease duration associated with neurofibrillary tangles. J Neurol Neurosurg Psychiat 1995; 59:266-270.


Rouleau GA, Clark AW, Rooke K, et al. SOD1 mutation is associated with accumulation of neurofilaments in amyotrophic lateral sclerosis. Ann Neurol 1996; 39:128-131.


Shibata N, Hirano A, Kobayashi M, et al. Intense superoxide dismutase-1 immunoreactivity in intracytoplasmic hyaline inclusions of familial amyotrophic lateral sclerosis with posterior column involvement. J Neuropathol Exp Neurol 1996; 55(4):481-490.


Takahashi H, Makifuchi T, Nakano R, et al. Familial amyotrophic lateral sclerosis with a mutation in the Cu/Zn superoxide dismutase gene. Acta Neuropathol 1994; 88:185-188.


Anderson PM, Nilsson P, Ala-Hurula V, et al. Amyotrophic lateral sclerosis associated with homozygosity for a Asp90Ala mutation in CuZn-superoxide dismutase. Nat Genet 1995; 10:61-66.


Andersen PM, Forsgren L, Binzer M, et al. Autosomal recessive adult-onset amyotrophic lateral sclerosis associated with homozygosity for Asp90Ala CuZn-superoxide dismutase mutation. A clinical and genealogical study of 36 patients. Brain 1996; 119:1153-1172.


Gurney ME, Pu H, Chiu AY, et al. Motor neuron degeneration in mice that express a human CuZn superoxide dismutase mutation. Science 1994; 264:1772-1775.


Tu P-H, Raju P, Robinson KA, et al. Transgenic mice carrying a human mutant superoxide dismutase transgene develop neuronal cytoskeletal pathology resembling human amyotrophic lateral sclerosis lesions. Proc Natl Acad Sci USA 1996; 93:3155-3160.


Bruijn LI, Becher MW, Lee MK, et al. ALS-linked SOD1 mutant G85R mediates damage to astrocytes and promotes rapidly progressive disease with SOD1-containing inclusions. Neuron 1997; 18:327-338.


Bergeron C, Muntasser S, Somerville MJ, Weyer L, Percy ME. Copper/Zinc superoxide dismutase mRNA levels are increased in sporadic amyotrophic lateral sclerosis. Brain Res 1994; 659:272-276.


Deng H-X, Hentati A, Tainer JA, et al. Amyotrophic lateral sclerosis and structural defects in CuZn superoxide dismutase. Science 1993; 261:1047-1051.


Troy CM, Shelanski ML. Down-regulation of copper/zinc superoxide dismutase causes apoptotic death in PC12 neuronal cells. Proc Natl Acad Sci USA 1994; 91:6384-6387.


Rabizadeh S, Gralla EB, Borchelt DR, et al. Mutations associated with amyotrophic lateral sclerosis convert superoxide dismutase from an antiapoptotic gene to a proapoptotitc gene: studies in yeast and neural cells. Proc Natl Acad Sci USA 1995; 92:3024-3028.


Reaume AG, Elliott JL, Hoffman EK, et al. Motor neurons in Cu/Zn superoxide dismutase-deficient mice develop normally but exhibit enhanced cell death after axonal injury. Nat Genet 1996; 13:43-47.


Bruijn LI, Houseweart MK, Kato S, et al. Aggregation and motor neuron toxicity of an ALS-linked SOD1 mutant independent from wild-type SOD1. Science 1998; 281:1851-1854.


Bredesen DE, Ellerby LM, Hart PJ, Wiedau-Pazos M, Valentine JS. Do posttranslational modifications of CuZnSOD lead to sporadic amyotrophic lateral sclerosis? Ann Neurol 1997; 42(2):135-137.


Pasinelli P, Houseweart MK, Brown RH, Jr, Cleveland DW. Caspase-1 and -3 are sequentially activated in motor neuron death in CuZn superoxide dismutase-mediated familial amyotrophic lateral sclerosis. Proc Natl Acad Sci USA 2000; 97(25):13901-13906.


Li M, Ona VO, Guégan C, et al. Functional role of caspase-1 and caspase-3 in an ALS transgenic mouse model. Science 2000; 288:335-339.


Migheli A, Piva R, Atzori C, Troost D, Schiffer D. c-Jun, JNK/SAPK kinases and transcription fact NF-kB are selectively activated in astrocytes, but not motor neurons, in amyotrophic lateral sclerosis. J Neuropathol Exp Neurol 1997; 56(12):1314-1322.


He BP, Strong MJ. Motor neuronal death in amyotrophic lateral sclerosis (ALS) is not apoptotic. A comparative analysis of ALS and chronic aluminum neurotoxicity in New Zealand white rabbits. J Neuropathol Appl Neurobiol 2000;26:1-13.


Ono S, Imai T, Aso A, et al. Alterations in skin glycosaminoglycans in patients with ALS. Neurology 1998; 51:399-404.


Hirano A. Cytopathology of amyotrophic lateral sclerosis. In: Rowland LP, ed. Amyotrophic lateral sclerosis and other motor neuron disorders. New York: Raven Press, 1991: 91-101.


Hirano A, Kurland LT, Sayre GP. Familial amyotrophic lateral sclerosis. Arch Neurol 1967; 16:232-242.


Chou SM. Motor neuron inclusions in ALS are heavily ubiquitinated. J Neuropathol Exp Neurol 1988; 47:334.


Murayama S, Mori H, Ihara Y, et al. Immunocytochemical and ultrastructural studies of lower motor neurons in amyotrophic lateral sclerosis. Ann Neurol 1990; 27:137-148.


Leigh P, Swash M. Cytoskeletal pathology in motor neuron disease. In: Rowland LP, ed. Advances in Neurology. Amyotrophic lateral sclerosis and other motor neuron diseases. New York: Raven Press, 1991: 115-124.


Chou SM. Neuropathology of amyotrophic lateral sclerosis: new perspectives on an old disease. J Formos Med Assoc 1997; 96(7):488-498.


Wong N, He BP, Strong MJ. Characterization of neuronal intermediate filament protein expression in cervical spinal motor neurons in sporadic amyotrophic lateral sclerosis (ALS). J Neuropathol Exp Neurol 2000; 59(11):972-982.


Migheli A, Pezzulo T, Attanasio A, Schiffer D. Peripherin immunoreactive structures in amyotrophic lateral sclerosis. Lab Invest 1993; 68(2):185-191.


Shaw PJ, Eggett CJ. Molecular factors underlying selective vulnerability of motor neurons to neurodegeneration in amyotrophic lateral sclerosis. J Neurol 2000; 247(Suppl 1):117-127.


Geisler N, Kaufmann E, Fischer S, Plessman U, Weber K. Neurofilament architecture combines structural principles of intermediate filaments with carboxy-terminal extensions increasing in size between triplet proteins. EMBO 1983; 2:1295-1302.


Ching GY, Liem RKH. Assembly of type IV neuronal intermediate filaments in nonneuronal cells in the absence of preexisting cytoplasmic intermediate filaments. J Cell Biol 1993; 122:1323-1335.


Lee MK, Xu Z, Wong PC, Cleveland DW. Neurofilaments are obligate heteropolymers in vivo. J Cell Biol 1993; 122:1337-1350.


Sihag RK, Nixon RA. Identification of Ser-55 as a major protein kinase A phosphorylation site on the 70-kDa subunit of neurofilaments. J Biol Chem 1991; 266:18861-18867.


Nixon RA, Shea TB. Dynamics of neuronal intermediate filaments: a developmental perspective. Cell Motil Cytoskel 1992; 22:81-91.


Côte F, Collard J-F, Julien J-P. Progressive neuronopathy in transgenic mice expressing the human neurofilament heavy gene: a mouse model of amyotrophic lateral sclerosis. Cell 1993; 73:35-46.


Julien J-P, Côte F, Collard J-F. Mice overexpressing the human neurofilament heavy gene as a model of ALS. Neurobiol Aging 1995; 16(3):487-492.


Xu Z, Cork LC, Griffin JW, Cleveland DW. Increased expression of neurofilament subunit NF-L produces morphological alterations that resemble the pathology of human motor neuron disease. Cell 1993; 73:23-33.


Beaulieu J-M, Nguyen MD, Julien J-P. Late-onset death of motor neurons in mice overexpressing wild-type peripherin. J Cell Biol 1999; 147(3):531-544.


Bergeron C, Beric-Maskarel K, Muntasser S, et al. Neurofilament light and polyadenylated mRNA levels are decreased in amyotrophic lateral sclerosis motor neurons. J Neuropathol Exp Neurol 1994; 53:221-230.


Crow JP, Ye YZ, Strong MJ, et al. Superoxide dismutase catalyzes nitration of tyrosines by peroxynitrite in the rod and head domains of neurofilament-L. J Neurochem 1997; 69:1945-1953.


Wong N, Strong MJ. Nitric oxide synthase expression in cervical motor neurons of sporadic amyotrophic lateral sclerosis. Eur J Cell Biol 1998; 77:338-343.


Chou SM, Wang HS, Taniguchi A. Role of SOD-1 and nitric oxide/cyclic GMP cascade on neurofilament aggregation in ALS/MND. J Neurol Sci 1996; 139(Suppl.):16-26.


Bergeron C, Petrunka C, Weyer L. Copper/zinc superoxide dismutase expression in the human nervous system. Correlation with selective neuronal vulnerability. Am J Pathol 1996; 148(1):273-279.


Pardo CA, Xu Z, Borchelt DR, et al. Superoxide dismutase is an abundant component in cell bodies, dendrites, and axons of motor neurons and in a subset of other neurons. Proc Natl Acad Sci USA 1999; 32:954-958.


Shaw PJ, Chinnery RM, Thagesen H, Borthwick GM, Ince PG. Immunocytochemical study of the distribution of the free radical scavenging enzymes Cu/Zn superoxide dismutase (SOD1); MN superoxide dismutase (MN SOD) and catalase in the normal human spinal cord and in motor neurons. J Neurol Sci 1997; 147(2):115-125.


Chou SM, Wang HS, Komai K. Colocalization of NOS and SOD1 in neurofilament accumulation within motor neurons of amyotrophic lateral sclerosis: an immunohistochemical study. J Chem Neuroanat 1996; 10:249-258.


Beal FM, Ferrante RJ, Browne SE, et al. Increased 3-nitrotyrosine in both sporadic and familial amyotrophic lateral sclerosis. Ann Neurol 1997; 42:646-654.


Ferrante RJ, Shinobu LA, Schulz JB, et al. Increased 3-nitrotyrosine and oxidative damage in mice with a human copper/zinc superoxide dismutase mutation. Ann Neurol 1997; 42:326-334.


Crow JP, Sampson JB, Zhuang Y, Thompson JA, Beckman JS. Decreased zinc affinity of amyotrophic lateral sclerosis-associated superoxide dismutase mutants leads to enhance catalysis of tyrosine nitration by peroxynitrite. J Neurochem 1997; 69:1936-1944.


Strong MJ, Sopper MM, Crow JP, Strong WL, Beckman JS. Nitration of the low molecular weight neurofilament (NFL) is equivalent in sporadic amyotrophic lateral sclerosis and control cervical spinal cord. Biochem Biophys Res Comm 1998; 248(1):157-164.


Strong MJ, Sopper MM, He BP. In vitro reactive nitrating species toxicity in dissociated spinal motor neurons from NFL (-/-) and HNFL transgenic mice. Neurology 2001; 56(Suppl 3):A83-A84.


Figlewicz DA, Krizus A, Martinoli MG, et al. Variants of the heavy neurofilament subunit are associated with the development of amyotrophic lateral sclerosis. Hum Mol Genet 1994; 3:1757-1761.


Rooke K, Figlewicz DA, Han FY, Rouleau GA. Analysis of the KSP repeat of the neurofilament heavy subunit in familial amyotrophic lateral sclerosis. Neurology 1996; 46(3):789-790.


Tomkins J, Usher P, Slade JY, et al. Novel insertion in the KSP region of the neurofilament heavy gene in amyotrophic lateral sclerosis (ALS). Neuroreport 1998; 9(17):3670-3697.


Al-Chalabi A, Andersen PM, Nilsson D, et al. Deletions of the heavy neurofilament subunit tail in amyotrophic lateral sclerosis. Hum Mol Genet 1999; 8(2):157-164.


Vechio JD, Bruijn LI, Xu Z, Brown RH, Jr., Cleveland DW. Sequence variants in human neurofilament proteins: absence of linkage to familial amyotrophic lateral sclerosis. Ann Neurol 1996; 40:603-610.


Strong MJ, Strong WL, Jaffe H, et al. Phosphorylation state of the native high molecular weight neurofilament subunit protein (NFH) from cervical spinal cord in sporadic amyotrophic lateral sclerosis. J Neurochem 2001; 76:1315-1325.


Siklos L, Englehardt J, Harati Y, et al. Ultrastructural evidence for altered calcium in motor nerve terminals in amyotrophic lateral sclerosis. Ann Neurol 1996; 39(2):203-216.


Masui Y, Mozai T, Kakehi K. Functional and morphometric study of the liver in motor neuron disease. J Neurol 1985; 232:15-19.


Nakano Y, Hirayama K, Terao K. Hepatic ultrastrucutral changes and liver dysfunction in amyotrophic lateral sclerosis. Arch Neurol 1987; 44:103-106.


Wiedemann FR, Winkler K, Kuznetsov A, et al. Impairment of mitochondrial function in skeletal muscle of patients with amyotrophic lateral sclerosis. J Neurol Sci 1998; 156:65-72.


Fujita K, Yamauchi M, Shibayama K, et al. Decreased cytochrome C oxidase activity but unchanged superoxide dismutase and glutathione peroxidase activities in the spinal cords of patients with amyotrophic lateral sclerosis. J Neurosci Res 1996; 45:276-281.


Bowling AC, Schulz JB, Brown RH, Jr., Beal MF. Superoxide dismutase activity, oxidative damage, and mitochondrial energy metabolism in familial and sporadic amyotrophic lateral sclerosis. J Neurochem 1993; 61:2322-2325.


Browne SE, Bowling AC, Baik MJ, et al. Metabolic dysfunction in familial, but not sporadic, amyotrophic lateral sclerosis. J Neurochem 1998; 71:281-287.


Swerdlow RH, Parks JK, Cassarino DS, et al. Mitochondria in sporadic amyotrophic lateral sclerosis. Exp Neurol 1998; 153:135-142.


Curti D, Malaspina A, Facchetti G, et al. Amyotrophic lateral sclerosis: oxidative enery metabolism and calcium homeostasis in peripheral blood lymphocytes. Neurology 1996; 47:1060-1064.


Ince P, Stout N, Shaw P, et al. Parvalbumin and calbindin D-28K in the human motor system and in motor neuron disease. Neuropathol Appl Neurobiol 1993; 19(4):291-299.


Alexianu ME, Ho BK, Mohamed AH, et al. The role of calcium-binding proteins in selective motoneuron vulnerability in amyotrophic lateral sclerosis. Ann Neurol 1994; 36(6):846-858.


Elliott JL, Snider WD. Parvalbumin is a marker of ALS-resistant motor neurons. Neuroreport 1995; 15(6):449-452.


Siklos L, Engelhardt JI, Alexianu ME, et al. Intracellular calcium parallels motoneuron degeneration in SOD-1 mutant mice. J Neuropathol Exp Neurol 1998; 57(6):571-587.


Knirsch U, Sturm S, Reuter A, et al. Calcineurin A and calbindin immunoreactivity in the spinal cord of G93A superoxide dismutase transgenic mice. Brain Res 2001; 889:234-238.


Vanselow BK, Keller BU. Calcium dynamics and buffering in oculomotor neurones from mouse that are particularly resistant during amyotrophic lateral sclerosis (ALS)-related motor neuron disease. J Physiol 2000; 552.2:433-445.


Przedborksi S, Donaldson DM, Murphy PL, et al. Blood superoxide dismutase, catalase and glutathione peroxidase activities in familial and sporadic amyotrophic lateral sclerosis. Neurodegeneration 1996; 5:57-64.


Przedborksi S, Donaldson D, Jakowec M, et al. Brain superoxide dismutase, catalase, and glutathione peroxidase activities in amyotrophic lateral sclerosis. Ann Neurol 1996; 39:158-165.


Shaw PJ, Ince PG, Falkous G, Mantle D. Oxidative damage to protein in sporadic motor neuron disease spinal cord. Ann Neurol 1995; 38:691-695.


Beckman JS, Beckman TW, Chen J, Marshall PA, Freeman BA. Apparent hydroxyl radical production by peroxynitrite: implications for endothelial injury from nitric oxide and superoxide. Proc Natl Acad Sci USA 1990; 87:1620-1624.


Rothstein JD, Jin L, Dykes-Hoberg M, Kuncl RW. Chronic inhibition of glutamate uptake produces a model of slow neurotoxicity. Proc Natl Acad Sci USA 1993; 90:6591-6595.


Carriedo SG, Yin HZ, Weiss JH. Motor neurons are selectively vulnerable to AMP/Kianate receptor-mediated injury in vitro. J Neurosci 1996; 16(13):4069-4079.


Rothstein JD, Van Kammen M, Levey AI, Martin LJ, Kuncl RW. Selective loss of glial glutamate transporter GLT-1 in amyotrophic lateral sclerosis. Ann Neurol 1995; 38:73-84.


Lin C-LG, Bristol LA, Jin L, et al. Aberrant RNA processing in a neurodegenerative disease: the cause for absent EAAT2, a glutamate transporter, in amyotrophic lateral sclerosis. Neuron 1998; 20:589-602.


Jackson M, Steers G, Leigh PN, Morrison KE. Polymorphisms in the glutamate transporter gene EAAT2 in European ALS patients. J Neurol 1999; 246:1140-1144.


Meyer T, Lenk U, Kuther G, et al. Studies of the coding region of the neuronal glutamate transporter gene in amyotrophic lateral sclerosis. Ann Neurol 1995; 37:817-819.


Meyer T, Münch C, Völkel H, Booms P, Ludolph AC. The EAAT2 (GLT-1) gene in motor neuron disease: absence of mutations in amyotrophic lateral sclerosis and a point mutation in patients with hereditary spastic paraplegia. J Neurol Neurosurg Psychiat 1998; 65:594-596.


Vartiainen N, Tikka T, Keinänen R, Chan PH, Koistinaho J. Glutamatergic receptors regulate expression, phosphorylation and accumulation of neurofilaments in spinal cord neurons. Neuroscience 1999; 93(5):1123-1133.


Lampson LA, Kushner PD, Sobel RA. Strong expression of class II major histocompatibility complex (MHC) antigens in the absence of detectable T cell infiltration in amyotrophic lateral sclerosis (ALS) spinal cord. J Neuropathol Exp Neurol 1988; 47:353-353.


Lampson LA, Kushner PD, Sobel RA. Major histocompatibility complex antigen expression in the affected tissues in amyotrophic lateral sclerosis. Ann Neurol 1990; 28:365-372.


Troost D, van den Oord JJ, de Jong JMBV, Swaab DF. Lymphocyte infiltration in the spinal cord of patients with amyotrophic lateral sclerosis. Clin Neuropath 1989; 8:289-294.


Kawamata T, Akiyama H, Yamada T, McGeer PL. Immunological reactions in amyotrophic lateral sclerosis brain and spinal cord tissue. Am J Pathol 1992; 140:691-707.


Barron KD, Marciano FF, Amundson R, Mankes R. Perineuronal glial response after axotomy of central and peripheral axons. A comparison. Brain Res 1990; 523:219-229.


Streit WJ. Microglial-neuronal interactions. J Chem Neuroanat 1993; 6:261-266.


Thanos S, Mey J, Wild M. Treatment of the adult retina with microglia-suppressing factors retards axotomy-induced neuronal degradation and enhances axonal regeneration in vivo and in vitro. J Neurosci 1993; 13:455-466.


Thanos S. The relationship of microglial cells to dying neurons during natural neuronal cell death and axotomy-induced degeneration of the rat retina. Eur J Neurosci 1991; 3:1189-1207.


Giulian D, Roberston C. Inhibition of mononuclear phagocytes reduces ischemic injury in the spinal cord. Ann Neurol 1990; 27:33-42.


Coffey PJ, Perry VH, Rawlins JNP. An investigation into the early stages of the inflammatory response following ibotenic acid-induced neuronal degeneration. Neuroscience 1990; 35:121-132.


Piani D, Frei K, Do KQ, Cuenod M, Fontana A. Murine brain macrophages induce NMDA receptor mediated neurotoxicity in vitro by secreting glutamate. Neurosci Lett 1991; 133:159-162.


Popovich PG, Reinhard JF, Jr., Flanagan EM, Stokes BT. Elevation of the neurotoxin quinolinic acid occurs following spinal cord trauma. Brain Res 1994; 633:348-352.


Thery C, Chamak B, Mallat M. Cytotoxic effect of brain macrophages on developing neurons. Eur J Neurosci 1991; 3:1155-1164.


Gehrmann J, Banati RB, Wiessnert C, Hossman K-A, Kreutzberg GW. Reactive microglia in cerebral ischemia: an early mediator of tissue damage? Neuropathol Appl Neurobiol 1995; 21:277-289.


Toku K, Tanaka J, Yano H, et al. Microglial cells prevent nitric oxide-induced neuronal apoptosis in vitro. J Neurosci Res 1998; 53:415-425.


Strong MJ, Gaytan-Garcia S, Jakowec D. Reversibility of neurofilamentous inclusion formation following repeated sublethal intracisternal inoculums of AlCl3 in New Zealand white rabbits. Acta Neuropathol 1995; 90(1):57-67.


He BP, Strong MJ. A morphological analysis of the motor neuron degeneration and microglial reaction in acute and chronic in vivo aluminum chloride neurotoxicity. J Chem Neuroanat 2000; 17(4):207-215.


Krieger C, Perry TL, Ziltener HJ. Amyotrophic lateral sclerosis: interleukin-6 levels in cerebrospinal fluid. Can J Neurol Sci 1992; 19(3):357-359.


Sekizawa T, Openshaw H, Ohbo K, et al. Cerebrospinal fluid interleukin-6 in amyotrophic lateral sclerosis: immunological parameter and comparison with inflammatory and noninflammatory central nervous system diseases. J Neurol Sci 1998; 154(2):194-199.


Demaerschalk BM, Strong MJ. Amyotrophic lateral sclerosis. Curr Treat Options Neurol 2000; 2:13-22.


Lacomblez L, Bensimon G, Leigh PN, Guillet P, Meininger V, for the Amyotrophic Lateral Sclerosis/Riluzole Study Group II. Dose-ranging study of riluzole in amyotrophic lateral sclerosis. Lancet 1996; 347(May 25):1425-1431.


Riviere M, Meininger V, Zeisser P, Munsat T. An analysis of extended survival in patients with amyotrophic lateral sclerosis treated with riluzole. Arch Neurol 1998; 55(4):526-528.


Kalra S, Cashman NR, Genge A, Arnold DL. Recovery of N-acetylaspartate in corticomotor neurons in patients with ALS after riluzole therapy. Neuroreport 1998; 9(8):1757-1761.


Blin O, Pouget J, Aubrespy G, et al. A double-blind, placebo-controlled trial of L-threonine in amyotrophic lateral sclerosis. J Neurol 1992; 239:79-81.


Tandan R, Bromberg MB, Forshew DA, et al. A controlled trial of amino acid therapy in amyotrophic lateral sclerosis: I. Clinical, functional, and maximum isometric torque data. Neurology 1996; 47:1220-1226.


The Italian ALS Study Group. Branched-chain amino acids and amyotrophic lateral sclerosis: a treatment failure? Neurology 1993; 43:2466-2470.


Gredal O, Werdelin L, Bak S, et al. A clinical trial of dextromethorphan in amyotrophic lateral sclerosis. Acta Neurol Scand 1997; 96:8-13.


Miller RG, Moore D, Young LA, et al. Placebo-controlled trial of gabapentin in patients with amyotrophic lateral sclerosis. Neurology 1996; 47:1383-1388.


Eisen A, Stewart H, Schulzer M, Cameron D. Antiglutamate therapy in amyotrophic lateral sclerosis: a trial using lamotrigine. Can J Neurol Sci 1993; 20:297-301.


Miller RG, Smith SA, Murphy JR, et al. A clinical trial of verapamil in amyotrophic lateral sclerosis. Muscle Nerve 1996; 19:511-515.


Lai EC, Felice KJ, Festoff BW, et al. Effect of recombinant human insulin-like growth factor on progression of ALS. A placebo controlled study. Neurology 1997; 49:1621-1630.


Ackerman SJ, Sullivan EM, Beusterien KM, et al. Cost effectiveness of recombinant human insulin-like growth factor I therapy in patients with ALS. Pharmacoeconomics 1999; 15:179-195.


Borasio GD, Robberecht W, Leigh PN, et al. A placebo-controlled trial of insulin-like growth factor-I in amyotrophic lateral sclerosis. Neurology 1998; 51:583-586.


ALS CNTF Treatment Study Group. A double-blind, placebo-controlled clinical trial of subcutaneous recombinant human ciliary neurotrophic factor (rHCNTF) in amyotrophic lateral sclerosis. Neurology 1996; 46:1244-1249.


Miller RG, Petajan J, Bryan WW, et al. A placebo-controlled trial of recombinant human ciliary neurotrophic (rhCNTF) factor in amyotrophic lateral sclerosis. Ann Neurol 1996; 39:256-260.


Smith RA, Melmed S, Sherman B, et al. Recombinant growth hormone treatment of amyotrophic lateral sclerosis. Muscle Nerve 1993; 16:624-633.


Brooke MH, Florence JM, Heller SL, et al. Controlled trial of thyrotropin releasing hormone in amyotrophic lateral sclerosis. Neurology 1986; 36:146-151.


Mitsumoto H, Salgado ED, Negroski D, et al. Amyotrophic lateral sclerosis: effects of acute intravenous and chronic subcutaneous administration of thyrotropin-releasing hormone in controlled trials. Neurology 1986; 36:152-159.


Imoto K, Saida K, Iwamura K, Saida T, Nishitani H. Amyotrophic lateral sclerosis: a double-blind crossover trial of thyrotropin-releasing hormone. J Neurol Neurosurg Psychiat 1984; 47:1332-1334.


Caroscio JT, Cohen JA, Zawodniak J, et al. A double-blind, placebo-controlled trial of TRH in amyotrophic lateral sclerosis. Neurology 1986; 36:141-145.


Brown RH, Jr., Hauser SL, Harrington H, Weiner HL. Failure of immunosuppression with a ten- to 14-day course of high-dose intravenous cyclophosphamide to alter the progression of amyotrophic lateral sclerosis. Arch Neurol 1986; 43:383-384.


Gourie-Devi M, Nalini A, Subbakrishna DK. Temporary amelioration of symptoms with intravenous cyclophosphamide in amyotrophic lateral sclerosis. J Neurol Sci 1997; 150:167-172.


Tan E, Lynn J, Amato AA, et al. Immunosuppressive treatment of motor neuron syndromes. Arch Neurol 1994; 51:194-200.


Meucci N, Nobile-Orazio E, Scarlato G. Intravenous immunoglobulin therapy in amyotrophic lateral sclerosis. J Neurol 1996; 243:117-120.


Olarte MR, Schoenfeldt RS, McKiernan G, Rowland LP. Plasmapheresis in amyotrophic lateral sclerosis. Ann Neurol 1980; 8:644-645.


Kelemen J, Hedlund W, Orlin JB, Berkman EM, Munsat TL. Plasmapheresis with immunosuppression in amyotrophic lateral sclerosis. Arch Neurol 1983; 40:752-753.


Drachman DB, Chaudhry V, Cornblath DR, et al. Trial of immunosuppression in amyotrophic lateral sclerosis using total lymphoid irradiation. Ann Neurol 1994; 35:142-150.


Appel SH, Stewart SS, Appel V, et al. A double-blind study of the effectiveness of cyclosporine in amyotrophic lateral sclerosis. Arch Neurol 1988; 45:381-386.


Lange DJ, Murphy PL, Diamond B, Appel V, et al. Selegiline is ineffective in a collaborative double-blind, placebo-controlled trial for treatment of amyotrophic lateral sclerosis. Arch Neurol 1998; 55:93-96.


Jossan SS, Ekblom J, Gudjonsson O, Hagbarth K-E, Aquilonius S-M. Double blind cross over trial with deprenyl in amyotrophic lateral sclerosis. J Neural Trans 1994; 41(Suppl.):237-241.


Mazzini L, Testa D, Balzarini C, Mora G. An open-randomized clinical trial of selegeline in amyotrophic lateral sclerosis. J Neurol 1994; 241:223-227.


Mendell JR, Chase TN, Engel WK. Amyotrophic lateral sclerosis. A trial of central monoamine metabolism and therapeutic trial of levodopa. Arch Neurol 1971; 25:320-325.


Norris FH, Tan Y, Fallat RJ, Elias L. Trial of oral physostigmine in amyotrophic lateral sclerosis. Clin Pharmacol Ther 1993; 54:680-682.


Aquilonius S-M, Askmark H, Eckernås S-A, et al. Cholinesterase inhibitors lack therapeutic effect in amyotrophic lateral sclerosis. A controlled study of physostigmine versus neostigmine. Acta Neurol Scand 1986; 73:628-632.


Aisen ML, Sevilla D, Edelstein L, Blass J. A double-blind placebo-controlled study of 3,4-diaminopyridine in amyotrophic lateral sclerosis patients on a rehabilitation unit. J Neurol Sci 1996; 138:93-96.


Askmark H, Aquilonius S-M, Gillberg P-G, et al. Functional and pharmacokinetic studies of tetrahydroaminoacridine in patients with amyotrophic lateral sclerosis. Acta Neurol Scand 1990; 82:253-258.


Olson WH, Simons JA, Halaas GW. Therapeutic trial of tilorone in ALS: lack of benefit in a double-blind, placebo-controlled study. Neurology 1978; 28:1293-1295.


Rivera VM, Grabois M, Deaton W, Breitbach W, Hines M. Modified snake venom in amyotrophic lateral sclerosis. Arch Neurol 1980; 37:201-203.


Cole N, Siddique T. Genetic disorders of motor neurons. Sem Neurol 1999; 19(4):407-418.


Siddique T, Figlewicz DA, Pericak-Vance MA, et al. Linkage of a gene causing familial amyotrophic lateral sclerosis to chromosome 21 and evidence of genetic-locus heterogeneity. N Engl J Med 1991; 324:1381-1384.


Chance PF, Rabin BA, Ryan SG, et al. Linkage of the gene for an autosomal dominant form of juvenile amyotrophic lateral sclerosis to chromosome 9q34. Am J Hum Genet 1998; 62:633-640.


Rabin BA, Griffin JW, Crain BJ, et al. Autosomal dominant juvenile amyotrophic lateral sclerosis. Brain 1999; 122:1539-1550.


Siliceo EO, Arriada-Mendicoa N, Balderrama J. Juvenile familial amyotrophic lateral sclerosis: four cases with long survival. Dev Med Child Neurol 1998; 40:425-428.


Hentati A, Bejaoui K, Pericak-Vance MA, et al. Linkage of recessive familial amyotrophic lateral sclerosis to chromosome 2q33-q35. Nat Genet 1994; 7:425-428.


Hentati A, Ouahchi K, Pericak-Vance MA, et al. Linkage of a common locus for recessive amyotrophic lateral sclerosis. Am J Hum Genet 1997; 61:A279.


Van Laere MJ. Paralysie bulbo-pontine chronique progressive familiale avec surdité. Un cas de syndrome de Klippel-Trenaunay dans la même fratrie. Problèmes diagnostiques et génétiques. Rev Neurol (Paris) 1966; 115:289-295.


Kennedy WR, Alter M, Sung JH. Progressive proximal spinal and bulbar muscular atrophy of late onset. Neurology 1968; 18:671-680.


Harding AE, Thomas PK, Baraitser M, et al. X-linked recessive bulbospinal neuronopathy: a report of ten cases. J Neurol Neurosurg Psychiat 1982; 45:1012-1019.


La Spada AR, Wilson EM, Lubahn DB, Harding AE, Fischbeck KH. Androgen receptor gene mutations in X-linked spinal and bulbar muscular atrophy. Nature 1991; 352:77-79.


Parboosingh JS, Figlewicz D, Krizus A, et al. Spinobulbar muscular atrophy can mimic ALS: the importance of genetic testing in male patients with atypical ALS. Neurology 1998; 49:568-572.


Mitsumoto H, Sliman RJ, Schafer IA, et al. Motor neuron disease and adult hexosaminidase A deficiency in two families: evidence for multisystem degeneration. Ann Neurol 1985; 17:378-385.


Cashman NR, Antel JP, Hancock LW, et al. N-acetyl-b-hexosaminidase b locus defect and juvenile motor neuron disease: a case study. Ann Neurol 1986; 19:568-572.


Rubin M, Karparti G, Wolfe LS, et al. Adult onset motor neuronopathy in the juvenile type of hexosaminidase A and B deficiency. J Neurol Sci 1988; 87:103-119.


Banerjee P, Siciliano L, Oliveri D, et al. Molecular basis of an adult form of b-hexosaminidase B deficiency with motor neuron disease. Biochem Biophys Res Comm 1991; 181(1):108-115.


Andersen PM, Morita M, Brown RH, Jr. Genetics of amyotrophic lateral sclerosis: an overview. In: Brown RH, Jr., Meininger V, Swash M, eds. Amyotrophic lateral sclerosis. London: Martin Dunitz Ltd., 2000: 223-250.


From the Department of Clinical Neurological Sciences, The University of Western Ontario, London, Ontario, Canada
Received April 18, 2001. Accepted in final form July 19, 2001.
Reprint requests to: MJ Strong, Room 7OF10, University Campus, London Health Sciences Centre, 339 Windermere Road, London, Ontario, Canada, N6A 5A5

Can. J. Neurol. Sci. 2001; 28: 285-298


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