Genetic Characterization of a Cohort of Italian Patients with Congenital Adrenal Hyperplasia Due to 21-Hydroxylase Deficiency

Introduction Defects in the steroid 21-hydroxylase gene (CYP21A2) cause\r\n21-hydroxylase deficiency (21OHD), the main cause of congenital adrenal\r\nhyperplasia (CAH). The disease shows a broad spectrum of clinical forms,\r\nranging from severe or classical (salt wasting, SW, and simple\r\nvirilizing, SV), to mild late onset or nonclassical (NC). 21OHD affects\r\n1 in 15,000 in its severe classic form and 1 in 200-1000 in its mild NC\r\nform. There are many studies reporting the frequency of CYP21A2\r\npathogenic variants in different populations; however, few of them\r\nprovide comprehensive information about Italian patients. Here, we\r\npresent genetic results from a cohort of 245 unrelated Italian\r\nindividuals with clinical diagnosis of CAH due to 21OHD.\r\nMethods A specific polymerase chain reaction (PCR) protocol combined\r\nwith Sanger sequencing was used for CYP21A2 analysis. The multiplex\r\nligation-dependent probe amplification (MLPA) assay was employed for\r\ncopy number variation (CNV) determination.\r\nResults One hundred fourteen (46.5\%) of the index cases had the NC\r\nform, 57 (23.3\%) had the SV form, and 74 (30.2\%) presented the SW form\r\nof the disease. The most prevalent variant found in NC patients was the\r\np.Val282Leu (51.3\%), while the most frequent variants in the classical\r\nform were p.Ile173Asn (8.6\%) and c.293-13C>G (26.0\%). In our study,\r\nthe frequency of large rearrangements was 15.3\%, with CAH-X alleles\r\nrepresenting 40\% of all DEL/CONV. In addition, 12 alleles carried rare\r\nvariants, and 1 had a novel variant p.(Arg342Gln).\r\nWe observed phenotype-genotype correlation in 94.7\% of cases. A\r\ncomplete concordance was observed in Groups 0 (enzyme activity\r\ncompletely impaired) where all patients had the SW form as expected. In\r\nGroup A (0-1\% residual enzyme activity), 78.4\% of patients had the\r\nanticipated SW form while 21.6\% were diagnosed with the SV form. Within\r\nGroup B (similar to 2\% residual enzyme activity), 93.4\% of patients\r\nexhibited SV form and 6.5\% SW disease. Finally, 92.6\% and 7.4\% of\r\npatients belonging to Group C (enzyme partially impaired to similar to\r\n20-60\% residual activity) exhibited NC and SV phenotypes, respectively.\r\nConclusion This work, representing a comprehensive genetic study,\r\nexpanded the CYP21A2 variants spectrum of Italian patients with 21OHD\r\nand could be helpful in prenatal diagnosis and genetic counseling.