In Vitro Enzyme Assay of CYP21A2 Mutation (R483Q) by A Novel Method Using Liquid Chromatography-Electrospray Ionization Tandem Mass Spectrometry (LC-ESI-MS/MS).

Congenital adrenal hyperplasia (CAH) is one of the most common autosomal recessive disorders in humans, and 21-hydroxylase deficiency (21-OHD) accounts for 90 to 95% of all cases of CAH. Approximately 95% mutations are a consequence of recombination between the CYP21A2 and its highly homologous pseudogene CYP21A1P. Recently, other rare mutations have been identified, increasing the number of reported mutations to more than eighty. The in vitro enzyme assay for the detection of mutated 21-hydroxylase is a well-established method. In this study, we report the characterization of the R483Q mutation using a novel in vitro enzyme assay, liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). With this system, we evaluated the activity of the R483Q mutation. The enzyme activities of 21-hydroxylase in the convertion of progesterone to deoxycorticosterone (DOC), and 17-hydroxyprogesterone (17-OHP) to 11-deoxycortisol (11-DOF), were measured as 2.00 ± 0.25% and 1.89 ± 0.30% of the wild type, respectively. This result was in agreement with that of a previous report, which measured the activities using the (3)H labeled steroid assay. Our results suggest that the R483Q mutation is compatible with the simple virilizing form of 21-OHD and that the LC-ESI-MS/MS assay using picolinoyl derivatives is an alternative to the existing (3)H-labeled steroid assay for the characterization of the CYP21A2 mutation.