Abstract 506 Endocrinology & Diabetes II Platform, Saturday, 5/1

Background: Classic congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency occurs in 1:15,000 live births in most populations, and the less severe nonclassic form of CAH-21 affects about 1:1000. We investigated feasibility and diagnostic utility of genotyping 9 CYP21 mutations, linked chromosome 6p markers, and a Y chromosome marker from neonatal screening samples. Methods: Blood-impregnated filter paper (Guthrie cards) from 603 randomly chosen New Zealand neonates were genotyped blind to 17-hydroxyprogesterone (170HP) levels. Another 50 samples from Swiss and North American infants with correlative hormonal data were also genotyped. DNA was extracted and genespecific PCR was performed, CYP21 products were subjected to ligase detection reaction, simultaneously analyzing 9 CYP21 mutations; PCR products of other genes were subjected to direct gel analysis. Results: CYP21 genotyping indicated a heterozygote rate of 2.8% for classic mutations and 2% of nonclassic mutations in New Zealand neonates. None of these newborns was homozygous for CYP21 mutations. Q318X was the single most commonly identified heterozygous classic mutation. V281L was the only nonclassic mutation detected among the New Zealand neonates. There was a statistical difference between our genetic heterozygote detection rate for classic CAH (1 in 36) and those calculated from hormonal screening studies (1:77 for NZ and 1:60 for all populations). Genetic linkage disequilibrium was found between 2 CYP21 mutations and chromosome 6p markers. Among 50 samples of Swiss and North American origin, 21 were sent for genotyping because of elevated 17OHP levels on newborn screen. Ten proven to be affected (8 classic CAH and 2 nonclassic; 6 females). Among all affected infants serum equivalent 17OHP level is ranged from a normal low value of 15 nmol/L to a high of 14,000 nmol/L. Of the 2 infants with normal 17OHP, one was a compound heterozygote carrying the nonclassic P30L allele and the classic CYP21 null genotype. ACTH stimulation testing confirmed the diagnoses. Two of the five affected females had only clitoromegaly, while 3 males showed signs of salt wasting. Seven of 21 infants with elevated 17OHP levels(37.4 to 183 nmol/L) were preterm and proved to have normal genotypes. Two sick full-term infants showed high 17OHP levels but no mutations. Two other full-term newborns screened on first day of life had normal genotypes, despite markedly elevated 17OHP levels. Of the infants with normal 17OHP levels, three were heterozygous for CYP21 mutations. Conclusion: Guthrie cards can be used to accurately genotype CYP21 potentially enhancing specificity and sensitivity of CAH screening. The CYP21 heterozygote frequency for classic mutations is higher than expected based on genotype compared with that predicted by hormonal newborn screening. CYP21 genotype can aid in therapeutic decision-making where newborn screening 17OHP values are equivocal.