Identification of non-amplifying CYP21 genes when using PCR-based diagnosis of 21-hydroxylase deficiency in congenital adrenal hyperplasia (CAH) affected pedigrees

Steroid 21-hydroxylase deficiency is among the most common inborn errors ofmetabolism in man. Characterization of mutations in the 21- hydroxylasegene (CYP21) has permitted genetic diagnosis, facilitated by the polymerasechain reaction (PCR). The most common mutation is conversion of an A or Cat nt656 to a G in the second intron causing aberrant splicing of mRNA.Homozygosity for nt656G is associated with profoundly deficient adrenalcortisol and aldosterone synthesis, secondary hypersecretion of adrenalandrogens, and a severe form of congenital adrenal hyperplasia (CAH)characterized by ambiguous genitalia and/or sodium wasting in newborns.During the course of genetic analysis of CYP21 mutations in CAH families,we and others have noticed a number of relatives genotyped as nt656Ghomozygotes, yet showing no clinical signs of disease. A number of lines ofevidence have led us to propose that the putative asymptomatic nt656G/Gindividuals are incorrectly typed due to dropout of one haplotype duringPCR amplification of CYP21. For prenatal diagnosis, we recommend thatmicrosatellite typing be used as a supplement to CYP21 genotyping in orderto resolve ambiguities at nt656.