The implication of de novo 21-hydroxylase mutation in clinical and prenatal molecular diagnoses.

We studied 37 unrelated families with a history of 21-hydroxylase deficiency (CYP21D) for eight common mutations and gene deletions in the 21-hydroxylase (CYP21) gene. We found de novo mutations in the CYP21 gene in two CYP21D patients. Analysis for eight common mutations in the 21-hydroxylase gene as well as large gene deletions was accomplished using polymerase chain reaction (PCR) followed by amplified created restriction site (ACRS) or restriction fragment length polymorphism (RFLP) and Southern blot followed by hybridization to a CYP21-specific probe. Linkage analysis was performed using microsatellite markers flanking the CYP21 gene. Ten short tandem repeat (STR) markers were used to confirm parentage in the two de novo mutation cases. In two prenatal diagnosis cases, an intron 2-13A/C>G mutation was identified in the proband, but not in the fetus, although the proband and fetus had identical linkage markers. Subsequently, the mutation was confirmed to be absent in the parents' genome and misparentage was ruled out. Our findings are consistent with previous studies showing a de novo mutation frequency of approximately 1.0-1.5% in the CYP21 gene. This new mutation rate is high relative to the rate of approximately one in one million for other autosomal recessive disorders. Thus, the de novo mutation rate in the CYP21 gene is not negligible. It must be considered and discussed in prenatal diagnosis and genetic counseling for this relatively common inherited disorder.