Abstract:
The autosomal recessive disease steroid 21-hydroxylase deficiency (21-OHD) accounts for over 90% of congenital adrenal hyperplasia (CAH) cases. CAH patients have impaired cortisol biosynthesis and produce excess androgens which may result in ambiguous genitalia in affected females. Also, in the most severe cases aldosterone biosynthesis may be insufficient, resulting in a potentially lethal salt-wasting crisis. Classic (severe) CAH has been estimated to affect 1/23 344 New Zealanders and approximately 1/15 000 individuals worldwide.
DNA was extracted from 603 randomly selected neonates from 3 mm diameter dried blood spots that were surplus material from the New Zealand neonatal screening programme, Genotyping of the 21-OH gene (CYP21) was performed using the PCR/Ligase Detection Reaction (LDR) of Day et al. 1995. In addition genotyping of six microsatellite markers that span CYP21 was performed.
This work has shown that there was a higher frequency for carriers of classic 21-OHD (1/36) than expected (1/76) from the number of CAH cases detected by hormonal newborn screening (P=0.015). A unique spectrum of classic mutations was found; the usually rare mutation term3l8 was the most prevalent. This mutation was found to be in linkage disequilibrium with the microsatellite haplotype TNFa-5; D6S273-7, indicating that founder effects may have influenced the spectrum of mutations in New Zealand. The mild non-classic mutation L281 was found to be in linkage disequilibrium with the microsatellite haplotype TNFa-2; D6S273-5. Genetic testing proved to be a useful adjunct to the current neonatal CAH screening program, but the cost of routine molecular analysis is likely to be prohibitive.
In addition a rapid accurate molecular genetic strategy for prenatal diagnosis using uncultured amniocytes or chorionic villi samples has been developed. This approach utilises a PCR mediated sex determination and microsatellite markers for linkage analysis in conjunction with PCR/LDR for 2l-OH genotyping. Prenatal diagnosis of three at risk foetuses was undertaken.
