A case of hypoplastic left heart syndrome and bicuspid aortic valve in monochorionic twins.

The etiology of hypoplastic left heart syndrome (HLHS) remains unclear. Since a genetic cause for HLHS has not been obvious, it is generally considered to be inherited in a multifactorial manner. Studies of twins are valuable in elucidating the genetic contribution to a birth defect such as HLHS. We report a case of monochorionic twins in whom one has HLHS and the other has a bicuspid aortic valve. Predisposing genetic and environmental influences on individuals with identical genotypes, such as twins, may result in discordance of left-sided flow lesions.