Abstract 38

The most common form of Congenital Adrenal Hyperplasia is the deficiency of steroid 21-hydroxylase. In order to define CYP21B mutation profile in Brazilian patients, we genotyped 41 families with at least one individual affected with the classical form of 21-hydroxylase deficiency, representing 74 unrelated alleles. Disease-causing alleles were characterised by three different approaches: Southern blot analysis with three restriction enzymes, allele-specific oligonucleotide hybridization and allele-specific PCR. Distinct alleles were recognised by TaqI C4B RFLP, gene duplications or deletions of either CYP21A + C4B or CYP21B + C4B, large gene conversion and eight mutations that might be introduced into CYP21B from CYP21A by microconversion events. It was detected at least one mutation in 24 different disease-causing alleles which represent about 85% of the affected alleles in those families. The frequency of 30 kb deletion of CYP21B was lower than that described for Caucasians. The mutation Sp2 (abnormal splice in intron 2) showed the highest frequency (24.65%) and was present mainly in salt-wasting patients, although it was detected in some patients with the simple virilizing form of the disease. Conversely, I172N (missense mutation in exon 4) showed a frequency of 18.91% and was found mostly in patients affected with the simple virilizing form of the disease. Other 5 mutations were determined in low frequency and CL6 (cluster of three missense mutations in exon 6) was not found in any of the tested alleles. Financial support: CNPq, FAPESP, CAPES, FAEP-UNICAMP.