Three cases of amyotrophic lateral sclerosis in a common occupational environment.

Three unrelated school teachers taught in the same school classroom for 2-5 years and subsequently developed amyotrophic lateral sclerosis (ALS) over an 18-year period. This clustering was not accompanied by an increased death rate for ALS in the county where the teachers lived and worked. Statistical analysis revealed that ALS as the cause of death for three teachers from the same school would be highly improbable as a random event. These findings suggest that the patient's shared school environment may have been a source of exposure to an agent pathogenetically significant in the development of their disease.