Season of birth in amyotrophic lateral sclerosis.

While studying birth cohort issues, the authors focused also on the seasons of birth in amyotrophic lateral sclerosis (ALS). The analyses were based on computerized death records of Swiss mortality statistics 1969-1993. The results confirm an excess of births in spring months. They suggest that risk factors in ALS can be acquired very early in life, thus introducing a long latency period.