Identification and functional characterization of a novel mutation P459H and a rare mutation R483W in the CYP21A2 gene in two Chinese patients with simple virilizing form of congenital adrenal hyperplasia

Background: Steroid 21-hydroxylase deficiency (21-OHD) is the most common cause of congenital adrenal hyperplasia (CAH). Clinically, 21-OHD is categorized into salt-wasting, simple-virilizing (SV), and non-classical (NC) forms. It is well recognized that a good correlation exists between genotype and clinical phenotype of CAH. Aim: The aim of this study was to identify CYP21A2 gene mutations in 2 Chinese patients with SV CAH along with their parents and other family members. Study design and results: By direct sequencing the CYP21A2 gene, a novel mutation, P459H, was detected in 1 patient; and a previously described uncharacterized mutation, R483W, was found in another patient. The 21-hydroxylase activities were determined by measuring the converting rate of progesterone to 11-deoxycorticosterone in COS-7 cells overexpressed with these mutated proteins. Our results revealed significantly reduced enzyme activity in both mutants: residual activity of P459H and R483W towards progesterone was 6.8%±2.1 and 2.9%±1.5, respectively compared to that of the wild type. We also demonstrated the loss of 21-hydroxylase activities using a three-dimensional model of CYP21A2. Conclusion: Both R483W and P459H mutations are confirmed to be related to NC CAH by in vitro functional study, with phenotype variance of R483W in Tunisian and Chinese patients. This study will aid in predicting disease severity and in facilitating family genetic counseling.