BackgroundIn familial hyperaldosteronism type I (FH-I), glucocorticoid treatment suppresses adrenocorticotrophic hormone-regulated hybrid gene expression and corrects hyperaldosteronism.ObjectiveTo determine whether the wild-type aldosterone synthase genes, thereby released from chronic suppression, are capable of functioning normally.MethodsWe compared mid-morning levels of plasma potassium, plasma aldosterone, plasma renin activity (PRA) and aldosterone: PRA ratios, measured with patients in an upright position, and responsiveness of aldosterone levels to infusion of angiotensin II (AII), for 11 patients with FH-I before and during long-term (0.8–14.3 years) treatment with 0.25–0.75 mg/day dexamethasone or 2.5–10 mg/day prednisolone.ResultsDuring glucocorticoid treatment, hypertension was corrected in all. Potassium levels, which had been low (< 3.5 mmol/l) in two patients before treatment, were normal in all during treatment (mean 4.0 ± 0.1 mmol/l, range 3.5–4.6). Aldosterone levels during treatment [13.2 ± 2.1 ng/100 ml (mean ± SEM)] were lower than those before treatment (20.1 ± 2.5 ng/100 ml,P< 0.05). PRA levels, which had been suppressed before treatment (0.5 ± 0.2 ng/ml per h), were unsuppressed during treatment (5.1 ± 1.5 ng/ml per h,P< 0.01) and elevated (> 4 ng/ml per h) in six patients. Aldosterone: PRA ratios, which had been elevated (> 30) before treatment (101.1 ± 25.9), were much lower during treatment (4.1 ± 1.0,P< 0.005) and below normal (< 5) in eight patients. Surprisingly, aldosterone level, which had not been responsive (< 50% rise) to infusion of AII for all 11 patients before treatment, remained unresponsive for 10 during treatment.ConclusionsApparently regardless of duration of glucocorticoid treatment in FH-I, aldosterone level remains poorly responsive to AII, with a higher than normal PRA and a low aldosterone: PRA ratio. This is consistent with there being a persistent defect in functioning of wild-type aldosterone synthase gene.