Discordance for achalasia in identical twins.

Twenty-year-old twin sisters, believed monozygotic on the basis of extensive blood grouping and cytogenetic studies, are reported. One twin demonstrated classical clinical, radiologic, and manometric features of achalasia, while similar studies in her sister documented perfectly normal esophageal motor function. Genetically determined damage to the esophageal parasympathetic innervation is, therefore, not a likely cause for the esophageal motor dysfunction in achalasia.