Two intronic variants of CYP11B1 and CYP17A1 disrupt mRNA splicing and cause congenital adrenal hyperplasia (CAH).

Objectives Congenital adrenal hyperplasia (CAH) is an autosomal recessive inherited disorder of steroidogenesis.11β-hydroxylase deficiency and 17α-hydroxylase deficiency are two forms of CAH caused by defects of CYP11B1 and CYP17A1 respectively. Case presentation Two rare intronic variants were identified in suspected CAH patients. Though not located at the classic splicing sites, these two variants perturbed splicing based on minigene assays. One variant, NM_000497.4: c.240-157T>G of CYP11B1 identified in subject 1, resulted in the retention of 136 intronic nucleotides. The other variant, NM_000102.4: c.754-6 A>G of CYP17A1 identified in subject 2, leading to the retention of 5 intronic nucleotides. Both variants resulted in out-of-frame alteration of the respective transcript. Conclusion Cryptic splicing variants in the intronic regions contribute to the genetic defects of CAH. Minigene assay is useful to confirm the splice altering effect and make a definitive molecular diagnosis.