The role of exogenous risk factors in amyotrophic lateral sclerosis in Wakayama, Japan.

The incidence of ALS in Wakayama Prefecture has been markedly higher than that elsewhere in the world. Recently, however, the incidence has gradually decreased, especially in men, and the age at onset has shifted to the elderly, indicating the possible role of exogenous factors in the development of ALS. To evaluate factors related to the disease, we conducted a retrospective study.