Mutations of the Steroid 21-Hydroxylase Gene in an Argentinian Population of 36 Patients with Classical Congenital Adrenal Hyperplasia

Abstract

In several studies carried out in USA and Europe, gene deletions, large gene conversions and six point mutations accounted for over 90% of the mutated alleles reported in classical congenital hyperplasia (CAH). In order to know the relative frequencies of mutations in a Latin-American population, the CYP21 active gene was analyzed in 42 patients with CAH belonging to 36 families attending two Argentinian clinics. The salt wasting form was diagnosed in 24 index cases and the simple virilized form in 12. When available, parents were also studied. DNA was extracted from peripheral blood leukocytes and specific PCR amplification of four different fragments of the CYP21 gene was carried out, followed by electrophoresis of the amplified product. The four fragments include segments of the gene containing the six most frequently reported abnormalities in classical CAH: IN2, EX3, R356W, cluster EX6 and I172N. Point mutations were studied by allelic specific oligonucleotide hybridization; Q318X was studied by digestion of the PCR product with PsT1 restriction enzyme and electrophoresis on 6% non-denaturing polyacrylamide gels. Deletions and macroconversions as well as confirmation of homozygote point mutations were studied by Southern blotting. Percentage distribution of abnormalities was as follows: deletion/macroconversion 18, IN2 18, I172N 15.3, Q318X 13.8, R356W 5.5, EX3 2.7, cluster EX6 0, not characterized 26.7. The complete genotype could be determined in 20 families while in 12 additional ones, the mutation was detected in one allele. Deletion/macroconversion, IN2, EX3 and Q318X were detected more frequently in salt wasting patients while I172N and R356W were found in simple virilized patients. However, genotype was not always concordant with phenotype. It is concluded that there are differences in the frequency of several gene mutations and in that of deletion/macroconversion between this Latin-American population and several reported American and European populations. In particular the percentage of deletion/macroconversion, IN2, EX3 and cluster EX6 was lower while I172N was higher in our Latin-American population. Furthermore the frequency of mutations not characterized was larger. This information is useful to delineate appropriate strategies for prenatal diagnosis in this particular population.