Amyotrophic lateral sclerosis: Epidemiology and risk factors

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease of motor neurons, invariably leading to progressive paralysis and death in 3–5 years from onset. ALS has an annual incidence of 2/100,000 and a prevalence of 6/100,000. The disease is more common in males and in Caucasian ethnicities and its incidence rises with advancing age. Age at onset and site of onset (bulbar vs. spinal) are the two main prognostic factors in ALS. The only certain risk factors for ALS are positive family history, male gender, and advancing age; among environmental factors, cigarette smoking is supported by the most robust evidence, whereas others are less well documented. However, most epidemiological studies on environmental risk factors in ALS are limited by methodological flaws. Future researches should be performed according to more stringent criteria and on larger cohorts, and they should also aim to capture the complex interplay between genetic and environmental factors in ALS pathogenesis.