CYP21A2 intronic variants causing 21-hydroxylase deficiency

Congenital adrenal hyperplasia (CAH) is an autosomal recessive disorder mainly caused by defects in the steroid 21-hydroxylase gene (CYP21A2). Most of CYP21A2 mutations result from intergenic recombinations between CYP21A2 and closely linked CYP21A1P pseudogene. Rare mutations not generated by gene conversion account for 5–10% of 21-hydroxylase deficiency alleles. Intronic variants represent only a little part of these but their effect on the protein is generally deleterious. The aim of this paper is to provide a comprehensive literary review regarding all intronic CYP21A2 pathological variants reported to date. In addition, we describe three novel causing disease variants in our patients affected by the classic form of CAH: IVS4-1G>A, IVS5-8T>A, IVS8-2A>G. In silico analysis revealed that all these substitutions affect the splicing process leading to a non-functional protein. Based on these results, we are able to classify them as pathological variants according to the patient's phenotype.