Anencephaly, twins and HLA-B27.

A patient with a twin pregnancy where both infants were affected with anencephaly is reported, and the world's literature on anencephaly in twins is summarized. The anomalies were diagnosed by ultrasound during the prenatal period. Studies of the genetic histocompatible lymphocyte antigens (HLA) types of both parents were performed, and they failed to demonstrate the HLA-B27 locus in either. Anencephaly in twins is an unusual phenomenon, with concordance even more rare. The possibility that anencephaly is a heterogeneous entity, both morphologically and genetically, and its relationship to the HLA locus are discussed.