Amyotrophic lateral sclerosis in dizygotic twins.

A pair of dizygotic twins developed typical amyotrophic lateral sclerosis during adulthood. The concordance for this disease in these two patients of nonconsanguineous parentage with no family history of the disorder suggests the possibility of sublethal intrauterine injury to anterior horn cells. Infectious or toxic exposure during the twins' intimately shared milieu in the prenatal period could have resulted in a neuronal "abiotrophy" that would not have become clinically apparent until decades later. If such a prenatal neuronal injury plays a role in the pathogenesis of amyotrophic lateral sclerosis, it becomes clear that attempts at experimental animal transmission of the disease from affected adults would fail even if the offending agent were viral.