Prenatal diagnosis of fragile (X) syndrome.

A fragile site (q27) of the X chromosome has been associated with X-linked mental retardation, and the prenatal diagnosis of the fragile (X) syndrome has been shown to be possible. It is suggested that both fluorodeoxyuridine and methotrexate in thymidine-deficient media be used to demonstrate the fragile (X) in cultured amniotic fluid cells. The fetus diagnosed in utero demonstrated the dolichocephaly, large ears, flattened malar area, and large testes characteristic of the fragile (X) syndrome in the newborn period.