In ALS, there is generally a striking dissimilarity in the degree of involvement of the upper motor neurons (UMNs) and the lower motor neurons (LMNs), the body regions affected, the degrees of involvement of other systems, especially cognition and behavior, and the progression rates among clinical phenotypes ( Ravits and La Spada 2009). In a recent epidemiological analysis of ALS combining 37 studies, the mean age for typical ALS disease onset (adult onset) was estimated at 61.8 ± 3.8 yr (range 54–67 yr) and the mean age for ALS diagnosis at 64.4 ± 2.9 yr (range 58–68 yr) ( Chio et al. In most cases, disease onset occurs during late adulthood, but juvenile (before 25 yr) and “young-onset” ALS cases (before 45 yr), respectively, represent ∼1% and ∼10% of all cases ( Turner et al. The median survival period following onset is independent of sex and is usually 2–4 yr ( Logroscino et al. Men are slightly more frequently affected than women, with a male:female incidence rate ratio of 1.4 ( Logroscino et al. 1996).ĪLS is the most common form of motor neuron disease, with a mean incidence of 2.8/100,000 in Europe and 1.8/100,000 in North America, and a mean prevalence of 5.40/100,000 in Europe and 3.40/100,000 in North America ( Chio et al. 2004) and (3) reactive gliosis, which corresponds to hypertrophy of glial cells in the motor cortex and spinal cord in the areas of degeneration ( Murayama et al. 1986) (2) degeneration and loss of Betz cells (large pyramidal cell neurons) in the primary motor cortex and degeneration of the lateral corticospinal tracts, which contain the axons projecting from the primary motor cortex to the motor neurons ( Hammer et al. The major neuropathological features of ALS are (1) extensive loss of lower motor neurons from the anterior horns of the spinal cord and brainstem ( Hughes 1982 Ghatak et al. The term “amyotrophic lateral sclerosis” was coined by the French neurologist Jean-Martin Charcot in the 1800s: “amyotrophic” refers to muscular atrophy, and “lateral sclerosis” describes the scarring or hardening of tissues in the lateral spinal cord. The pathogenic mechanism(s) in ALS remain unknown, but active propagation of the pathology neuroanatomically is likely a primary component.Īmyotrophic lateral sclerosis (ALS) is a progressive, fatal neuromuscular disease characterized by degeneration of the upper and lower motor neurons resulting in dysfunction of the somatic muscles of the body ( Cleveland and Rothstein 2001 Bradley 2009). Conversely, multiple phenotypes can be caused by a single gene mutation thus, a single molecular mechanism could be compatible with clinical heterogeneity. Because the same phenotypes can have multiple causes, including different gene mutations, there may be multiple molecular mechanisms causing ALS, implying that the disease is a syndrome. The varying phenotypes can be so distinctive that they would seem to have differing biology. Typical, or “classical,” ALS is associated with simultaneous upper motor neuron (UMN) and lower motor neuron (LMN) involvement at disease onset, whereas atypical forms, such as primary lateral sclerosis and progressive muscular atrophy, have early and predominant involvement in the UMN and LMN, respectively. ò»VÂò®º™éø“ddpŠÉÂsñ *KŠ.Amyotrophic lateral sclerosis (ALS) is primarily characterized by progressive loss of motor neurons, although there is marked phenotypic heterogeneity between cases.
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