Antenatal diagnosis of Niemann-Pick disease in a twin pregnancy.

An Ashkenazi Jewish woman had a child with Niemann-Pick disease in her first marriage. She subsequently remarried a man who was also heterozygous for the condition and conceived twins. Prenatal diagnostic tests were performed and one twin was shown to be homozygous and the other heterozygous for Niemann-Pick disease. The problems of prenatal diagnosis and counselling in twin pregnancies are discussed.