Renin–aldosterone response, urinary Na/K ratio and growth in pseudohypoaldosteronism patients with mutations in epithelial sodium channel (ENaC) subunit genes

Abstract

Multi-system pseudohypoaldosteronism (PHA) is a rare syndrome of aldosterone unresponsiveness characterized by symptoms of severe salt-losing caused by mutations in one of the genes that encode α, β or γ subunit of epithelial sodium channels (ENaC). We examined long-term changes in the renin–aldosterone response in patients with different mutations. Four PHA patients were followed-up for 7–22 years. Patient A with a heterozygous Gly327Cys missense mutation in αENaC is a mild case and patients B, C and D are severe cases. Two additional patients with renal PHA served as controls. In patient A, serum aldosterone and plasma renin activity (PRA) decreased with age, PRA reaching near normal values at age 11. In contrast, patients B–D showed a positive correlation between age and aldosterone ( r > 0.86 for all). In patient B with Arg508 stop mutation, aldosterone reached 166 nmol/L at age 19 (>300-fold higher than normal). Urinary Na/K ratios normalized gradually with age in all patients. Growth curves of the patients were reflective of the severity of PHA and compliance with salt therapy. Functional expression studies in oocytes showed that ENaC with αGly327Cys mutation, as observed in patient A, showed nearly 40% activity of the wild type ENaC. In contrast, stop mutation as in patient B reduces ENaC activity to less than 5% of the normal. Our results demonstrate distinct genotype–phenotype relationships in multi-system PHA patients. The degree of ENaC function impairment affects differently the renin–aldosterone system and urinary Na/K ratios. The differences observed are age-dependent and PHA form specific.