Genetics in Congenital Adrenal Hyperplasia Due to 21-Hydroxylase Deficiency and Clinical Implications

Of all congenital adrenal hyperplasia (CAH), 95% to 99% is 21-hydroxylase deficiency (21OHD), an autosomal recessive disease. 21OHD is due to an insufficiency of 21-hydroxylase enzyme, which is encoded by the CYP21A2 gene and involved in cortisol and aldosterone production. The clinical presentation differs widely from severe classic to mild nonclassic CAH. 21OHD represents one of the most complex and at the same time intriguing topics in human genetics and its molecular diagnosis involves ongoing challenges. To provide a meticulous presentation of the topic, we searched the past and present literature, including original articles and reviews from PubMed, ScienceDirect, Web of Science, Embase, and Scopus, using search terms for genetics of 21OHD, 21OHD variants, molecular diagnosis of 21OHD, and 21OHD genetic testing. We offer a comprehensive review focusing on recent developments, new concepts, and conclusions.