Novel mutations in the SCNN1A gene causing Pseudohypoaldosteronism type 1.

Pseudohypoaldosteronism type 1 (PHA1) is a rare inherited disease characterized by resistance to the actions of aldosterone. Mutations in the subunit genes (SCNN1A, SCNN1B, SCNN1G) of the epithelial sodium channel (ENaC) and the NR3C2 gene encoding the mineralocorticoid receptor, result in systemic PHA1 and renal PHA1 respectively. Common clinical manifestations of PHA1 include salt wasting, hyperkalaemia, metabolic acidosis and elevated plasma aldosterone levels in the neonatal period. In this study, we describe the clinical and biochemical manifestations in two Chinese patients with systemic PHA1. Sequence analysis of the SCNN1A gene revealed a compound heterozygous mutation (c.1311delG and c.1439+1G>C) in one patient and a homozygous mutation (c.814_815insG) in another patient, all three variants are novel. Further analysis of the splicing pattern in a minigene construct showed that the c.1439+1G>C mutation can lead to the retainment of intron 9 as the 5'-donor splice site disappears during post-transcriptional processing of mRNA. In conclusion, our study identified three novel SCNN1A gene mutations in two Chinese patients with systemic PHA1.

Identification of a novel WNK4 mutation in Chinese patients with pseudohypoaldosteronism type II.

BACKGROUND: It has been reported that mutations in WNK1 and WNK4 cause pseudohypoaldosteronism type II (PHA2), an autosomal dominant renal disease. WNK kinase proteins are expressed in the kidney and regulate ion transport including the thiazide-sensitive sodium chloride cotransporter (NCC). In this report, we screened 4 Chinese PHA2 pedigrees for WNK4 mutations, identified a novel mutation, and studied its effects on NCC protein trafficking in vitro. METHODS: The patients' genomic DNA was extracted from peripheral leukocytes. Sequence analysis was performed by PCR amplification of the 19 exons of WNK4. The wild-type or mutant WNK4 was coexpressed with NCC in HEK293 cells. We measured the effect of wild-type WNK4 compared to the mutant WNK4 on NCC protein surface expression. RESULTS: A novel missense mutation in WNK4, K1169E, was identified in 1 of the 4 pedigrees. Analysis of confocal images showed that K1169E lost its inhibitory effect on NCC surface expression compared to wild-type WNK4 when expressed in HEK293 cells, while it did not change NCC total protein expression. CONCLUSIONS: We identified an unreported disease-causing WNK4 missense mutation, K1169E, in 1 Chinese PHA2 pedigree. This mutation appears to be a 'loss of function' of NCC inhibition and suggests that some important functional roles lie in the 2nd coiled-coil domain of WNK4.