1 ANALYSIS OF POINT MUTATIONS (PM) OF CYP 21B GENE IN PATIENTS WITH 21-HYDROXYLASE DEFICIENCY (CAH)

Abstract

It has been described that only 25% of lesions in the active CYP 21B gene can be detected by Southern blotting, i.e.. 30 KPB deletions and large gene conversions (D-C). The remaining 75% are probably PM. The 8 most frequent PM are present in the pseudogene, suggesting that they are the consequence of gene microconversions. D-C, as well as several PM or microconversions (codon 318, C → T; codon 234-238, T-T-T → A-A-A; exon 3, -8BP and codon 172, T → A. but in only 4 patients (p) were studied in 20 p with CAH (12 salt losers, SL, 2 simple virilizing form, SV, and 2 late onset non-classical, NC, CAH). By POR technique, D-C were found in 3 p (6 alleles, a) while the alteration in codon 234-238 was detected in 1 p (2a). PM in codon 318 was detected in 4 p (4 a) after digestion with restriction endonuclease (RE) PST 1 followed by fragment analysis, and in exon 3 in 2 p (2 a) with RE ALU-1. Codon 172 PM was discarded by the SSCP technique in the 4 p studied. Alterations were detected in 50% of SL, 50% if them being D-C, 33% codon 318 PM and 17% exon 3-8BP deletions. One p with SV was homozygous for codon 234-238 M. It is concluded that by combining PCR and RE fragment analysis several of the most frequent PM can be studied in a simple and rapid way when a change in a normal restriction site has taken place.