A Compound Heterozygote Case of Type II Aldosterone Synthase Deficiency

Abstract

An infant with failure to thrive, persistent hyponatremia and episodic vomiting and diarrhea was admitted to hospital at 9 months of age, and the diagnosis of type II aldosterone synthase deficiency was confirmed by plasma and urinary steroid determinations. The entire coding sequence of the aldosterone synthase gene (CYP11B2) was determined (both strands) in the affected infant, an unaffected sibling, and both parents. An exon 3 mutation (C554T, leading to amino acid T185I) was found in the father and both siblings, and an exon 9 mutation (A1492G, leading to T498A) was found in the affected infant and the mother. Expression of the mutant sequences in COS cells showed steroidogenic patterns typical of aldosterone synthase type II deficiency, including very low levels of aldosterone synthesis (< or =0.5% of wild-type enzyme) consistent with the low aldosterone levels in the patient's plasma. Both mutations in this compound heterozygote localize to the beta 3-sheet in the cytochrome P450 enzyme structure, as does the previously characterized R181W mutation. This region of the enzyme is not part of the putative structural core, but mutations to this region suggest that it is important for conferring the unique ability of aldosterone synthase to catalyze efficient oxygenation of the C(18) carbon of steroid substrates.

Mineralocorticoid Receptors: Distribution and Activation

“…It is not possible from such a location to be unequivocal on which gene came first: aldosterone synthase has 11β hydroxylase activity, human 11β hydroxylase low but detectable levels of aldosterone synthase activity [16], and bovine 11β hydroxylase is responsible for both 11β hydroxylation and sequential oxidation of carbon 18 to yield aldosterone. What provides a pointer, however, is a consideration of the evolutionary appearance of cortisol and aldosterone, which strongly suggests that the primary gene product had predominant 11β hydroxylase activity.…”

Evaluation of CYP11Bs expression in HCT116 cells

“…Các đặc tính của enzyme CYP11B2 thường được nghiên cứu trong tế bào khỉ COS-1 hoặc tế bào COS-7 [11,12]. Mặc dù dòng tế bào COS rất phổ biến nhưng chưa chắc đã phải là dòng tế bào tối ưu cho biểu hiện các enzyme CYP11B người.…”

Fission yeast Schizosaccharomyces pombe as a new system for the investigation of corticosterone methyloxidase deficiency-causing mutations

“…The findings of Pascoe et al showed that V386A itself caused a small but steady reduction of the 18-hydroxylation activity while the 11␤-hydroxylation and the 18-oxidation activities were similar to that of the wild type. Furthermore, several studies use this double mutation R181W/V386A as positive control for the investigation of CMO II deficiency patients [10,15].…”

“…The estimation of the enzymatic activity of CYP11B2 is carried out either by using radioactive-labelled DOC (or B) and a radioactive detection method [e.g. the high performance thin layer chromatography (HPTLC) and autoradiography] [14,15] or by radioimmunoassay [7,15]. For this reason, neither of these methods can be considered as high or even medium throughput testing system that can be applied to investigate several mutations on the same time.…”