Prenatal DNA analysis in four embryos/fetuses at risk of 21-hydroxylase deficiency.

Prenatal diagnosis of 21-hydroxylase deficiency (21-OHD) in two unrelated embryos and two fetuses was attempted with the Southern hybridization method using the 21-hydroxylase (21-OHase) complementary DNA as a probe. The two embryos whose genomic DNA was extracted from their chorionic villi both had four TaqI fragments (3.7 kb, 3.2 kb, 2.4 kb and 2.3 kb) identical to those of their respective parents and normal controls, while the DNA from each proband of these two families lacked with the 3.7 kb and the 2.3 kb fragments corresponding to the functional 21-OHase gene (21-OHase B gene). These findings indicated that none of the embryos examined were deletion homozygotes for the 21-OHase B gene. In the two fetuses, only amniotic fluid cells were available for prenatal diagnosis. The results of Southern hybridization analysis were uninformative since all family members, including the probands and fetuses, had all four TaqI fragments. Linkage studies between 21-OHD and human leukocyte antigen (HLA) haplotypes and those between the disease and restriction fragment length polymorphisms of the 4th complement gene revealed that the fetus of one family was normal. The other fetus could not be diagnosed because a recombination between the class I HLA and the 21-OHD loci had occurred in this family.