Genetic analysis of the cytochrome P-450c17 alpha (CYP17) and aldosterone synthase (CYP11B2) in Japanese patients with 17 alpha-hydroxylase deficiency

OBJECTIVE To determine the clinical and molecular genetic characterization of two Japanese patients with 17 alpha -hydroxylase deficiency, we analysed the 17 alpha -hydroxylase/17,20-lyase gene (CYP17). Next, to clarify the m echanism of hypoaldosteronism in 17 alpha -hydroxylase deficiency, we analy sed the expression of aldosterone synthase (CYP11B2) messenger RNA and sequ enced CYP11B2 in these patients. PATIENTS Patient 1 (46 XY), phenotypically female, sought medical attention for hypertension, amenorrhea and infantile genitalia. Patient 2 (46 XX), p henotypically female, presented for hypertension and amenorrhea, Hormonal d ata in both patients showed decreased levels of sex steroids, cortisol, ald osterone and plasma renin activity and extreme elevation of deoxycortisol. DESIGN Direct sequencing of CYP17 and CYP11B2 was performed using genomic D NA from the patients. An expression studies of mutated forms of CYP17 was p erformed using COS-1 cells. The expression of CYP11B2 messenger RNA in mono nuclear leucocytes (MNLs) of these patients and normal subjects was measure d using the competitive polymerase chain reaction method. The effect of ren in secretion stimulation on the levels of CYP11B2 messenger RNA in MNLs of normal subjects was also studied. RESULTS We detected two novel genetic defects in 17 alpha -hydroxylase. Seq uence analysis revealed one base pair deletion (T) at codon 243 in exon 4 i n patient 1. CYP17 in patient 2 contained a point mutation (C to T) at posi tion 415 in exon 8. Transfected cells of mutant from patient 1 had no 17 al pha -hydroxylase or 17,20-lyase activity. The R415C mutant protein showed v ery weak activity of 17 alpha -hydroxylase or 17,20-lyase activity. In the renin secretion stimulating test, the increase in CYP11B2 messenger RNA lev els in MNLs was parallel with that of plasma aldosterone concentration. The expression of CYP11B2 mRNA in NMLs of these patients was lower compared to controls. No mutations in CYP11B2, including the 5' flanking region, were found. CONCLUSIONS These results indicate that the novel mutations of the CYP17 ge ne found in these patients inactivate cytochrome P450c17 function, and that hypoaldosteronism in these patients may be partly explained by a decreased activity of aldosterone synthase, which is regulated at the transcriptiona l level.