In about 95% of cases, congenital adrenal hyperplasia (CAH) is caused by mutations in CYP21A2 gene encoding steroid 21-hydroxylase (21OH). Recently, we have reported four novel CYP21A2 variants in the Norwegian population of patients with CAH, of which p.L388R and p.E140K were associated with salt wasting (SW), p.P45L with simple virilising (SV) and p.V211M+p.V281L with SV to non-classical (NC) phenotypes. We aimed to characterise the novel variants functionally utilising a newly designed in vitro assay of 21OH enzyme activity and structural simulations and compare the results with clinical phenotypes. CYP21A2 mutations and variants were expressed in vitro. Enzyme activity was assayed by assessing the conversion of 17-hydroxyprogesterone to 11-deoxycortisol by liquid chromatography tandem mass spectroscopy. PyMOL 1.3 was used for structural simulations, and PolyPhen2 and PROVEAN for predicting the severity of the mutants. The CYP21A2 mutants, p.L388R and p.E140K, exhibited 1.1 and 11.3% of wt 21OH enzyme activity, respectively, in vitro. We could not detect any functional deficiency of the p.P45L variant in vitro; although prediction tools suggest p.P45L to be pathogenic. p.V211M displayed enzyme activity equivalent to the wt in vitro, which was supported by in silico analyses. We found good correlations between phenotype and the in vitro enzyme activities of the SW mutants, but not for the SV p.P45L variant. p.V211M might have a synergistic effect together with p.V281L, explaining a phenotype between SV and NC CAH.

Immunoassays of steroid hormones are still used in the diagnosis and monitoring of patients with congenital adrenal hyperplasia. However, cross-reactivity between steroids can give rise to falsely elevated steroid levels. Here, we compare the use of immunoassays and liquid chromatography–tandem mass spectrometry (LC–MS/MS) in the monitoring of patients with classic 21-hydroxylase deficiency (21OHD). Steroid profiles in different mutation groups (genotypes) were also compared. Fifty-five patients with classic 21OHD (38 women) were studied. Blood samples were collected in the morning after an overnight medication fast. LC–MS/MS and immunoassays were employed to assay 17-hydroxyprogesterone (17OHP), testosterone and androstenedione. In addition, 21-deoxycortisol (21DF), 11-deoxycortisol (11DF), corticosterone, deoxycorticosterone, cortisone and cortisol were analyzed by LC–MS/MS. Testosterone, androstenedione and 17OHP levels were consistently lower (by about 30–50%) when measured by LC–MS/MS compared with immunoassays, with exception of testosterone in men. There was a significant correlation between 21DF and 17OHP (r = 0.87, P < 0.001), but three patients had undetectable 21DF. Subjects with no enzyme activity had significantly lower mean 11DF concentrations than subjects with residual activity. The use of LC–MS/MS gives a more specific view of adrenal steroid levels in 21OHD compared with immunoassays, which seem to considerably overestimate the levels of 17OHP and androstenedione. Falsely elevated levels of 17OHP and androstenedione could lead to overtreatment with glucocorticoids.