In Situ Hybridization in Prenatal Diagnosis

We will develop significantly improved automated techniques for detecting the most commonly occurring cytogenetic abnormalities in interphase cells obtained by amniocentesis or chorionic villus sampling (CVS). Using DNA probes on interphase cells avoids the culturing required for routine cytogenetic analysis. This will reduce the time and cost of prenatal diagnosis and permit extension of the test to a larger segment of the at-risk population. Automation will be particularly important when fetal cells can be isolated from maternal blood samples. This would eliminate the risk of amniocentesis or CVS and extend fetal aneuploidy screening to virtually all pregnancies. We will use fluorescent DNA probe labeling and automated image analysis to quantify the numbers of chromosomes 21, 18, 13, X, and Y in interphase cells. Aneuploidies of these five chromosomes occur in approximately 2% of all prenatal diagnostic tests done for "advanced maternal age", and they account for the great majority of all viable cytogenetic abnormalities observed at amniocentesis or CVS. Rapid aneuploidy screening and sex determination will also assist situations involving newborns with multiple congenital anomalies or ambiguous genitalia, suggesting possible trisomy. Interphase cell analysis by in situ hybridization could provide a diagnosis in under 24 hours; a considerable difference compared to the 48-72 hours for conventional cytogenetics done on peripheral blood and 10-14 days for amniocentesis or CVS.