Prenatal diagnosis of steroid 21-hydroxylase deficiency by the modified polymerase chain reaction to detect splice site mutation in the CYP21 gene.

A splicing junction mutation at nucleotide 656 (A-> G substitution, I2G) in the steroid 21-hydroxylase gene (CYP21) is the most frequently detected mutation in patients with the salt-wasting and simple-virilizing forms of steroid 21-hydroxylase deficiency (approximately 60%). In this disease, prenatal diagnosis and treatment to minimize the effects of excess androgen in affected females has been advocated. Therefore, to detect the I2G mutation rapidly, accurately, and without the use of radioisotope, we developed a modified polymerase chain reaction (PCR) with a mismatched 3' nucleotide primer to introduce a new restriction site upon PCR amplification of the mutant allele. This allowed the mutant allele to be identified readily by restriction enzyme digestion of the PCR product, and subsequently this PCR product was subjected to restriction enzyme digestion for diagnosis. Chorionic villus biopsy samples (CVS) were obtained at 10 to 11 weeks gestation from two females carrying fetuses at risk for steroid 21-hydroxylase deficiency. Prenatal diagnosis was successful in both cases. One affected female was treated with dexamethasone to term. In the other case, treatment was withdrawn at an early stage when testing revealed a normal fetus. The results demonstrate the rapid and accurate detection of the I2G mutation by this method, thereby indicating the feasibility of for prenatal diagnosis of the I2G mutation.