Classical and nonclassical 21-hydroxylase deficiency: a molecular study of Argentine patients.

Objective: To characterize the molecular basis of the 21-hydroxylase deficiency in a group of Argentine patients presenting the classical and nonclassical forms of the disease.

Design: To analyse the frequency of point mutations in the CYP21 gene by DNA amplification and mutation detection.

Patients: Forty-one patients from 36 nonrelated families: 25 nonclassical (NC), 11 salt-wasting (SW) and five simple virilizing (SV). A total of 27 parents and 13 nonaffected siblings were also analysed.

Measurements: Basal steroid hormones and 17-hydroxyprogesterone levels following adrenal stimulation with adrenocorticotrophic hormone were measured, together with an analysis of 10 point mutations in the CYP21 gene.

Results: A total of 83% and 74.4% classical and nonclassical chromosomes, respectively, were characterized. The intron 2 mutation was the most prevalent among classical alleles. In addition, a high frequency for R356W was observed in both groups (13.3 and 6.9%, respectively), while V281L was the most frequent mutation among the nonclassical patients with a frequency of 39.5%. No alleles containing P30L were observed, and one de novo mutation (R356W) was found. A total of 68.3% patients were fully genotyped, and all but one showed no genotype/phenotype discrepancy. Though the cut-off value for post-ACTH 17-hydroxyprogesterone stimulation was 30.25 nmol/l (10.00 microg/l), the lowest value observed in the fully genotyped nonclassical group was 42.35 nmol/l (14.00 microg/l).

Conclusions: The high number of unidentified alleles in the nonclassical group suggests that less frequent mutations, or the presence of new ones, might be the cause of the disease in the Argentine population. Alternatively, the cut-off value in the ACTH-stimulated 17-hydroxyprogesterone test might overestimate the diagnosis of the nonclassical form by including some patients with heterozygous status.