MOLECULAR ANALYSIS OF CYP21 AND C4 GENES IN BRAZILIAN FAMILIES WITH THE CLASSICAL FORM OF STEROID 21-HYDROXYLASE DEFICIENCY

The most common enzymatic defect of steroid synthesis is deficiency of the adrenal steroid 21-hydroxylase. Inhibition of the formation of co rtisol results in an increased pituitary release of ACTH which in turn drives the adrenal cortex to overproduce androgens. This hormonal set ting affects the development of genetic females by misdirecting the di fferentiation of external genitalia towards the male type. Since the i solation of the gene encoding 21-hydroxylase enzyme in 1984, gene dele tions, large gene conversions, and microconversions have been reported to be responsible for the disease. In this paper, we report a study o f this genetic defect in 22 families with one or more affected offspri ng diagnosed as having the classical form of congenital adrenal hyperp lasia. The DNA from 30 patients was analyzed with three restriction en zymes. Hybridization with a 21-hydroxylase cDNA probe and the 5 'end o f a C4 genomic probe disclosed gene deletion in 7.3% (3/41) of the dis ease-related chromosomes. The rate of large gene conversion was 17.1%( 7/41), and no abnormality in the hybridization pattern was observed in 75.6% (31/41) of the disease alleles. Densitometry of the autoradiogr aphs was used to determine the ratio of the copy-number of the 21-hydr oxylase gene (CYP21B) to the copy-number of its pseudogene (CYP21A). D ifferences in phenotype, the low frequency of gene deletion, and the h igh frequency of gene conversion compared with other studies in differ ent populations indicated that 21-hydroxylase deficiency in the Brazil ian population may involve different molecular mutations.