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 erro rs of metabolism in man, Characterization of mutations in the 21-hydro xylase gene (CYP21) has permitted genetic diagnosis, facilitated by th e polymerase chain reaction (PCR), The most common mutation is convers ion of an A or C at nt656 to a G in the second intron causing aberrant splicing of mRNA. Homozygosity for nt656G is associated with profound ly deficient adrenal cortisol and aldosterone synthesis, secondary hyp ersecretion of adrenal androgens, and a severe form of congenital adre nal hyperplasia (CAH) characterized by ambiguous genitalia and/or sodi um wasting in newborns, During the course of genetic analysis of CYP21 mutations in CAH families, we and others have noticed a number of rel atives genotyped as nt656G homozygotes, yet showing no clinical signs of disease, A number of lines of evidence have led us to propose that the putative asymptomatic nt656G/G individuals are incorrectly typed d ue to dropout of one haplotype during PCR amplification of CYP21, For prenatal diagnosis, we recommend that microsatellite typing be used as a supplement to CYP21 genotyping in order to resolve ambiguities at n t656.