2016 Volume 63 Issue 3 Pages 301-310
Deficiency of steroid 11β-hydroxylase activity occurs in 5-8% of patients with congenital adrenal hyperplasia (CAH). The aim of the current study was to identify mutations in the CYP11B1 gene of a patient with CAH due to deficiency of steroid 11β-hydroxylase activity, and to study the functional and structural consequences of these mutations. A molecular genetic analysis of the CYP11B1 gene in this patient and her parents identified a known missense mutation g.5194G>C (p.D63H) and a novel 2 bp deletion mutation (g.9525_9526delCT, corresponding to p.L380V…R420X) in the patient. In vitro expression studies in COS7 cells revealed a decreased 11β-hydroxylase activity in the p.D63H mutant to 2.0±0.8% and in the p.L380V…R420X mutant to 0.2±2.2% for the conversion of 11-deoxycortisol to cortisol. Three dimensional homology models for the normal and mutant proteins were built by using the recently published x-ray structure of the human CYP11B2 as a template. Presumably, the g.9525_9526delCT mutation in CYP11B1 resulted in a truncated protein with a misfolded C-terminal domain that could not efficiently bind heme iron, substrate, and adrenodoxin and had lost its biochemical function. In summary, CAH due to steroid 11β-hydroxylase deficiency can be attributed to both the novel deletion mutation (g.9525_9526delCT, corresponding to p.L380V…R420X) and known missense mutation (g.5194G>C corresponding to p.D63H) in CYP11B1.