Search

We investigate the genetic etiology in a cohort of patients with a clinical, biochemical, and hormonal profile suggestive of a mild and transient form of pseudohypoaldosteronism type 1 (PHA1). Twelve patients with PHA1 from four different families with clinical and biochemical data were analyzed. The coding regions of NR3C2 and SCNN1A genes were sequenced. Human α-epithelial sodium channel (ENaC) wild-type (wt), αPhe226Cys and aPhe226Ser ENaC variants were expressed in Xenopus laevis oocytes to evaluate ENaC activity. The protein expression of α-ENaC wt and mutants was determined by Western blot. All patients were homozygotes for the p. Phe226Cys mutation of the α subunit of ENaC. In functional studies in X. laevis oocytes, p.Phe226Cys caused a significant reduction of ENaC activity (83% reduction), reduced the number of active ENaC mutant channels, and reduced the basal open probability compared with wt. Quantitative Western blot analysis revealed that the reduced activity of ENαC mutant channels was due to a reduced ENaC protein expression for the αPhe226Cys compared with wt. We present 12 patients from four different families with a mild and transient autosomal recessive PHA1 due to a novel homozygous missense mutation in the SCNN1A gene. Functional studies showed that the p.Phe226Cys substitution mutation in ENaC leads to a partial loss of function resulting mainly from both a decrease in the intrinsic ENaC activity and a reduction in channel expression at the protein level. The partial loss of ENaC function could explain the mild phenotype, variable expressivity, and the transient course of the disorder in these patients. [ABSTRACT FROM AUTHOR]