Sporadic ALS and chromosome 22: evidence for a possible neurofilament gene defect

Glia cells in amyotrophic lateral sclerosis: New clues to understanding an old disease?

In classic neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), the pathogenic concept of a cell-autonomous disease of motor neurons has been challenged increasingly in recent years. Macro- and microglial cells have come to the forefront for their role in multistep degenerative processes in ALS and respective disease models. The activation of astroglial and microglial cells occurs early in the pathogenesis of the disease and seems to greatly influence disease onset and promotion. The role of oligodendrocytes and Schwann cells remains elusive. In this review we highlight the impact of nonneuronal cells in ALS pathology. We discuss diverse glial membrane proteins that are necessary to control neuronal activity and neuronal cell survival, and summarize the contribution of these proteins to motor neuron death in ALS. We also describe recently discovered glial mechanisms that promote motor neuron degeneration using state-of-the-art genetic mouse technology. Finally, we provide an outlook on the extent to which these new pathomechanistic insights may offer novel therapeutic approaches.

Amyotrophic lateral sclerosis as a complex genetic disease

In complex diseases like ALS, there are multiple genetic and environmental factors all contributing to disease liability. The genetic factors causing susceptibility to developing ALS can be considered a spectrum from single genes with large effect sizes causing classical Mendelian ALS, to genes of smaller effect, producing apparently sporadic disease. We examine the statistical genetic principles that underpin this model and review what is known about ALS as a disease with complex genetics.

Amyotrophic lateral sclerosis: contemporary concepts in etiopathogenesis and pharmacotherapy

Among the neurodegenerative diseases associated with ageing, amyotrophic lateral sclerosis (ALS) remains the most devastating. The disease inexorably progresses, the vast majority of pharmacotherapies have failed to modify the disease course, death ensues on average within 5 years of symptom onset and increasing numbers of individuals are afflicted with the disease. However, significant advances in our understanding of the natural history of ALS and of the fundamental nature of the biological defect underlying motor neuron degeneration have been gained, providing hope for the development of novel pharmacotherapies for ALS. Among these is the recognition that ALS is a biologically heterogeneous disorder in which genetics, environment and ageing all interrelate. The observation of clinical heterogeneity, with initial clinical manifestations serving as predictors of survivorship, is of considerable importance in designing therapeutic trials. The presence of frontotemporal dysfunction in a subset of patients has led to increased interest in the relationship between ALS and the degenerative tauopathies. Ultimately, the degenerating motor neurons do not die alone. The contribution of both microglia and astrocytes to the degenerative process are increasingly recognised. Understanding how these processes interrelate has become critical to understanding the pharmacotherapy of ALS and in the design of clinical trials. This review will highlight recent epidemiological and neurochemical advances in our understanding of ALS, and place them into the context of understanding the development of novel treatment avenues for this devastating disease.

The basic aspects of therapeutics in amyotrophic lateral sclerosis

Once thought to be a single pathological disease state, amyotrophic lateral sclerosis (ALS) is now recognized to be the limited phenotypic expression of a complex, heterogeneous group of biological processes, resulting in an unrelenting loss of motor neurons. On average, individuals affected with the disease live <5 years. In this article, the complex nature of the pathogenesis of ALS, including features of age dependency, environmental associations, and genetics, is reviewed. Once held to be uncommon, it is now clear that ALS is associated with a frontotemporal dementia and that this process may reflect disturbances in the microtubule-associated tau protein metabolism. The motor neuron ultimately succumbs in a state where significant disruptions in neurofilament metabolism, mitochondrial function, and management of oxidative stress exist. The microenvironment of the neuron becomes a complex milieu in which high levels of glutamate provide a source of chronic excitatory neurotoxicity, and the contributions of activated microglial cells lead to further cascades of motor neuron death, perhaps serving to propagate the disease once established. The final process of motor neuron death encompasses many features of apoptosis, but it is clear that this alone cannot account for all features of motor neuron loss and that aspects of a necrosis-apoptosis continuum are at play. Designing pharmacological strategies to mitigate against this process thus becomes an increasingly complex issue, which is reviewed in this article.

Genetic epidemiology of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a late onset, rapidly progressive and ultimately fatal neurological disorder, caused by the loss of motor neurons in the brain and spinal cord. Familial aggregation of ALS, with an age-dependent but high penetrance, is a major risk factor for ALS. Familial ALS (FALS) is clinically and genetically heterogeneous. Three genes and linkage to four additional gene loci have been identified so far and may either predominantly lead to ALS (ALSI-ALS6) or cause multisystem neurodegeneration with ALS as an occasional symptom (tauopathies, ALS-dementia complex). This review presents a tentative classification of the "major" ALS genes and ALS "susceptibility" genes, that may act as susceptibility factors for neurodegeneration in interaction with other genetic or environmental risk factors. Considering that mutations in ALS genes explain approximately 10% of familial as well as sporadic ALS, and most remaining cases of the discase are thought to result form the interaction of several genes and environmental factors, ALS is a paradigm for multifactorial discases.

Leukemia inhibitory factor induces epidermal hyperplasia in patients with amyotrophic lateral sclerosis

We investigated the biochemical and morphologic alteration in skin of amyotrophic lateral sclerosis patients. We found an obvious high expression of leukemia inhibitory factor and distinct epidermal hyperplasia in the skin of amyotrophic lateral sclerosis patients compared with disease controls. The thickness and cell density, as well as the leukemia inhibitory factor immunostain density, of the epidermis in amyotrophic lateral sclerosis patients correlated positively with duration of illness. The striking fact was the significant epidermal hyperplasia correlating with leukemia inhibitory factor expression in amyotrophic lateral sclerosis patients (r = 0.94, p < 0.001). In vitro experiments revealed that leukemia inhibitory factor stimulated keratinocyte proliferation in primary keratinocyte culture and induced epidermal hyperplasia in skin organ culture. These findings lead to the hypothesis that a high expression of leukemia inhibitory factor is closely associated with epidermal hyperplasia in amyotrophic lateral sclerosis patients.

Heterogeneous expression of neurofilament proteins in forebrain and cerebellum during development: clinical implications for spinocerebellar ataxia

Using quantitative immunoblotting, we have measured the level of two mammalian neurofilament proteins, the 68-kDa NF-L and the 66-kDa NF-66 (alpha-internexin), in the rat CNS during development. NF-66 is localized in neurons and neuronal processes in both embryonic and postnatal brain. Importantly, NF-66 is more abundant than NF-L in both forebrain and cerebellum during development. The prevalence of NF-66 over NF-L is most pronounced in brain gray matter. The expression of both NF-66 and NF-L increases continuously during the first month after birth. In situ hybridization demonstrated that NF-66, but not NF-L is, expressed in the cerebellar granule cells. Our findings suggest that the neurofilaments are heterogeneous in developmental expression, among neuronal subtypes and in composition. Human NF-66 neurofilament has recently been mapped to chromosome 10q24. Careful analysis of the human genome map indicates NF-66 gene lies within the critical region of infantile-onset spinocerebellar ataxia (IOSCA). The characteristic developmental expression and spatial localization of the NF-66 gene suggests it as a candidate gene for the disease.

Clinical epidemiology of amyotrophic lateral sclerosis

The introduction of palliative therapies in amyotrophic lateral sclerosis (ALS) will alter the epidemiology of ALS as it is known now. Although incidence rates will remain unchanged in the near future, prevalence rates will likely increase dramatically. Better understanding of the age-specific presentation of motor neuron diseases worldwide will shed light on the vexing questions concerning the variable incidence rates in some countries and apparent incidence gradients in North America and Europe.

Amyotrophic lateral sclerosis is a multifactorial disease

Amyotrophic lateral sclerosis (ALS) is probably biphasic. An initial trigger(s) is followed by a terminal cascade coinciding with the onset of neurological deficits. The terminal cascade involves interactive multifactorial pathogenic mechanisms. Aging must play a crucial role leading to multiple defective or degraded gene products accumulating with progressing years. This in turn leads to failure of receptor integrity and resulting excitotoxicity, free radical accumulation, failure of neurotrophism, and possibly immunological disturbances. These events are predated by months or years by a trigger which is also likely to be multifactorial and cumulative. Evidence suggests that environmental factors may be important triggers. Failure of specific glutamate transporters and calcium binding proteins may account for selective vulnerability of the corticomotoneuronal system. It is postulated that in ALS the primary target cell is the corticomotoneuron or the local circuit interneurons which modulate its activity. Glia cells may play an important role in the demise of the corticomotoneuronal cell. The disordered corticomotoneuron induces excessive excitatory transmitter (glutamate?) release at the corticomotoneuronal-spinal-motoneuronal synapse resulting in the subsequent demise of this neuron.