Determination of the carriage of the «chimeric» CYP21A1P/CYP21A2 gene in families with a proband with non-classical congenital adrenal hyperplasia

Abstract

90% of cases of congenital adrenal hyperplasia (CAH) are associated with changes in the CYP21A2 gene, of which about 20% are in various “chimeric” CYP21A1P/CYP21A2 genes. The problem of identifying “chimeric” genes and the relationship of their various types with the CAH clinical forms is still relevant today. The study is devoted to the analysis of the “chimeric” CH4 gene in the non-classical form of CAH. We used the methods of PCR-RFLP analysis and Sanger sequencing. DNA samples of 3 probands with a non-classical form of CAH and their parents were analyzed. The use of PCR-RFLP analysis with CYP21A2 gene-specific primers did not allow us to identify “chimeric” genes in the parents of the probands, but made it possible to assume their presence in the probands themselves. Whereas a complex analysis using all methods and pseudogene and gene-specific primers showed the presence in each of the 3 probands of the “chimeric” CH4 gene in the compound heterozygous state. In the first case, with the I173N variant, in the second, with i2 splice, and in the 3rd, with the 30 kb deletion of the CYP21A2 gene. For molecular genetic analysis in families with 21-hydroxylase deficiency, it is necessary to use both the analysis of major point mutations and methods that detect deletion-duplication events in the CYP21A2 gene. The presence of a “chimeric” CH4 gene with a break point between positions chr6:38038514 and chr6:32038938 (GRCh38) in a compound with other pathogenic variants leads to the nonclassical form of CAH.