First-trimester prenatal diagnosis of the Nijmegen breakage syndrome and ataxia telangiectasia using an assay of radioresistant DNA synthesis.

Prenatal diagnosis was performed in two pregnancies at risk of the Nijmegen breakage syndrome. In one pregnancy, an affected fetus was diagnosed by demonstration of radioresistant DNA synthesis, using autoradiographic detection of incorporated tritiated thymidine in cultured chorionic villus cells. The diagnosis was confirmed in fetal skin fibroblasts. In the other case, the fetus appeared unaffected. Using the same procedure, unaffected fetuses were predicted from chorionic villus cells in two pregnancies at risk of ataxia telangiectasia, which is another genetic disorder showing the feature of radioresistant DNA synthesis. The present biochemical method for prenatal detection of Nijmegen breakage syndrome and ataxia telangiectasia can be used as a simplified alternative to the cytogenetic procedures reported earlier for ataxia telangiectasia.