A sequence variation in 3’UTR of CYP21A2 gene correlates with a mild form of Congenital Adrenal Hyperplasia

Congenital adrenal hyperplasia is mainly caused by the deficiency of the 21-hydroxylase enzyme coded by the CYP21A2 gene. However, some alleles inthe nonclassical form (NC-CAH) remain without identified mutations, suggesting the involvement of regulatory regions. Our objective was to study an allele carrying the variant *13 G>A in the 3’UTR of the CYP21A2 gene identified in some patients with NC-CAH in order to verify the possible implication of this variation with the phenotype observed. From all the subjects in whom the CYP21A2 gene was analysed, 14 patients and 7 relatives heterozygous or homozygous for the *13 G>A substitution in 3’UTR were selected. Sequencing of DNA, genotyping, multiplex ligation-dependent probe amplification (MLPA), in-vitro studies and bioinformatic analysis were performed.The haplotype of the *13 G>A allele resulted identical in all the subjects and no other concomitant mutations were found in the region extending from 3 Kb upstream the starting codon to the polyadenilation signal. MLPA analysis showed the monomodular structure of the allele composed by one C4A gene and one CYP21A2 gene without a second module with the CYP21A1P pseudogene. Bioinformatic analysis predicted a consistent alteration of the RNA folding due to this sequence variation and no miRNA target sequence in this region. In vitro studies confirmed a decreased expression level for the mRNA carrying the *13 G>A variation . In conclusion, this substitution in the 3’UTR of the gene seems to be implicated in the NC-CAH phenotype suggesting the importance of analysing also the untranslated regions.