Molecular Genetic Prenatal Diagnosis of Congenital Adrenal Hyperplasia Due to 21-Hydroxylase Deficiency by Allele-Specific Hybridization

The feasibility and accuracy of gene-specific molecular genetic diagnosis for congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency were studied in a group of 24 pregnancies at 25% risk of carrying an affected fetus. Chorionic villus sampling was performed in the majority of cases. Southern blot analysis was carried out to identify deletions or other gross rearrangements. In parallel, the polymerase chain reaction (PCR) was performed, followed by allele-specific oligonucleotide hybridization (ASO) for a panel of nine known mutations. Mutations were identified in 95% of the chromosomes examined. The molecular diagnosis was accurate in 23 of 24 infants. The most common mutation identified was an A-to-G transition in the second intron (52% of affected chromosomes), the result of an apparent gene conversion. One fetus carried homozygous deletion of CYP21 , which accounted for 13% of all affected chromosomes. Other mutations identified included an 8-bp deletion in the third exon (22%); Ile 172 to Asn, a nonconservative substitution, in the fourth exon (9%); and Gln 318 to term, a nonsense mutation, in the eighth exon (4%). No mutation was detected in CYP21 in 5% of obligate-affected chromosomes examined by these methods.