MUTATIONS OF THE STEROID 21-HYDROXYLASE GENE IN AN ARGENTINEAN POPULATION OF 36 PATIENTS WITH CLASSICAL CONGENITAL ADRENAL-HYPERPLASIA

In several studies carried out in USA and Europe, gene deletions, larg e gene conversions and six point mutations accounted for over 90% of t he mutated alleles reported in classical congenital hyperplasia (CAH). In order to know the relative frequencies of mutations in a Latin-Ame rican population, the CYP21 active gene was analyzed in 42 patients wi th CAH belonging to 36 families attending two Argentinian clinics. The salt wasting form was diagnosed in 24 index cases and the simple viri lized form in 12. When available, parents were also studied. DNA was e xtracted from peripheral blood leukocytes and specific PCR amplificati on of four different fragments of the CYP21 gene was carried out, foll owed by electrophoresis of the amplified product. The four fragments i nclude segments of the gene containing the sis most frequently reporte d abnormalities in classical CAH: IN2, EX3,R356W, cluster EX6 and I172 N. Point mutations were studied by allelic specific oligonucleotide hy bridization; Q318X was studied by digestion of the PCR product with Ps T1 restriction enzyme and electrophoresis on 6% nondenaturing polyacry lamide gels. Deletions and macroconversions as well as confirmation of homozygote point mutations were studied by Southern blotting. Percent age distribution of abnormalities was as follows: deletion/macroconver sion 18, IN2 18, I172N 15.3, Q318X 13.8, R356W 5.5, EX3 2.7, cluster E X6 0, not characterized 26.7. The complete genotype could be determine d in 20 families while in 12 additional ones, the mutation was detecte d in one allele. Deletion/macroconversion, IN2, EX3 and Q318X were det ected more frequently in salt wasting patients while I172N and R356W w ere found in simple virilized patients. However, genotype was not alwa ys concordant with phenotype. It is concluded that there are differenc es in the frequency of several gene mutations and in that of deletion/ macroconversion between this Latin-American population and several rep orted 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 fre quency of mutations not characterized was larger. This: information is useful to delineate appropriate strategies for prenatal diagnosis in this particular population.