Reverse dot-blot hybridization as an improved tool for the molecular diagnosis of point mutations in congenital adrenal hyperplasia caused by 21-hydroxylase deficiency.

BACKGROUND: More than 90% of cases of congenital adrenal hyperplasia (CAH) are caused by mutations of the CYP21 gene that result in deficiencies of the enzyme 21-hydroxylase. Allele-specific PCR, allele-specific oligonucleotide hybridization, and Southern blot analysis are the most common methods to detect point mutations and deletions in the CYP21 gene. METHODS AND
RESULTS: This report is the first application of the reverse dot-blot (RDB) assay for diagnosis of the nine most common point mutations in the CYP21 gene associated with CAH (P30L, g.659A>G or g.659C>G, I172N, I236N-V237E-M239K, V281L, g.1767-1768insT, Q318X, R356W, P453S). Normal and mutant oligonucleotides spanning these nine mutation sites were spotted onto a nylon membrane. DNA was extracted from dried blood spots, and exons encompassing mutations from samples to be tested were amplified and labeled with biotin-dUTP by PCR. These exons then were hybridized to membrane strips. Signal detection was achieved by chemiluminescence. Thirty clinically confirmed cases that were identified by the Texas Newborn Screening Program were tested. All mutations were subsequently confirmed by automated DNA sequencing.
CONCLUSION: The RDB method has the advantages of being accurate and cost-effective for the molecular diagnosis of CYP21 point mutations in CAH. It permits simultaneous detection of a panel of point mutations with only one hybridization per sample and could be automated to study many samples.