Epidemiology of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is the most common motor neuron disease. Loss of pyramidal and anterior horn motor neurons leads to progressive limb weakness, disability, dysarthria, dysphagia and respiratory insufficiency with a progressive fatal course. The incidence of ALS ranges between 1.5 to 2.5 for 100,000 per year. Although there are familial cases of ALS, about 90% are sporadic and of unknown etiology. Several exogenous risk factors have been documented. However, no convincing evidence has demonstrated in a reproducible manner an association between an environmental or lifestyle risk factor and ALS. Disease duration varies considerably, ranging from a few months to 10-15 years with a mean survival of about 36 months. Prognostic factors such as age, site of disease onset, nutritional, functional and respiratory status at the diagnosis or delay between beginning of the disease and diagnosis have been reported but they appear to be insufficient to explain prognostic variability. These last 15 years, development of supportive care for ALS patients and management in ALS centers may have contributed to improve survival. Finally, ALS centres, and particularly French ALS centres, have developed databases to improve our knowledge of ALS, phenotypic characterization, more accurate phenotype-genotype correlations and thus contribute to new therapeutics developments.