Prenatal quantitation of number of X-chromosomes by slot blot hybridization and autoradiography

Abstract

OBJECTIVE: To study the use of slot blot hybridization as a method of prenatal quantication of the number of X-chromosomes in chorionic villi samples. METHOD: DNA of chorionic villi from fetuses with karyotypes of 46,XY; 45,XO; 47,XXX; 69,XXX and 48,XXXX were extracted, slot blotted and hybridized to the following radioactive probes: β 0.9, FVIII, pY 3.4 and pBLUR. DNA of chorionic villi from five other fetuses with unknown karytypes were similarly blotted and hybridized. Autoradiography with pre-exposed films was carried out and the density of each of the hybridized bands was scanned by a laser densitomer. RESULTS: It was found that with increasing amounts of DNA in the samples, the intensity of the bands hybridized with FVIII and β 0.9 probes increased proportionately. However, the intensity of the bands obtained with the probes pY 3.4 and pBLUR (probes containing multiple repeat sequences) varied little with increasing DNA concentrations. The ratios of radioactivity obtained for the two probes FVIII/β 0.9 were well correlated with the number of X-chromosomes in the samples. Calculations of the FVIII/β 0.9 ratio for the five samples with the unknown karyotypes gave a correct prediction of the number of X-chromosomes in each case. CONCLUSION: Slot blot hybridization can be used as a method of prenatal quantitation of the number of X-chromosomes in chorionic villi samples. The method could be useful for rapid prenatal diagnosis of other numerical chromosomal abnormalities.