Prenatal diagnosis of X-linked mental retardation with fragile (X) using fetoscopy and fetal blood sampling.

Pure fetal blood, (uncontaminated with maternal blood), was obtained from two male fetuses at risk for X-linked mental retardation with fragile(X) at Xq27-28 by direct vision fetoscopy and fetal blood sampling. Both were shown to have this fragile site on the X chromosome while nine other fetal blood samples from pregnancies at risk for other X-linked diseases, or haemoglobinopathies did not show fragile sites at Xq27-28, and a blood sample from an abortus showed only 1 fragile site in 95 mitoses. Both pregnancies were terminated, cultures established from fetal tissues, and the diagnosis confirmed in each case. The problems of demonstrating the fragile site in tissues other than fetal blood in these pregnancies (such as amniotic fluid cells or fibroblasts from fetal tissues) are discussed.