Novel compound heterozygous CLCNKB gene mutations (C.1755A>G/c.848_850delTCT) cause classic bartter syndrome

Abstract

Wang C, Chen Y, Zheng B, Zhu M, Fan J, Wang J, Jia Z, Huang S, Zhang A. Novel compound heterozygous CLCNKB gene mutations (c.1755A>G/c.848_850delTCT) cause classic Bartter syndrome. Am J Physiol Renal Physiol 315: F844–F851, 2018. First published February 14, 2018; doi:10.1152/ajprenal.00077.2017.—In-activated variants in CLCNKB gene encoding the basolateral chloride channel ClC-Kb cause classic Bartter syndrome characterized by hypokalemic metabolic alkalosis and hyperreninemic hyperaldosteronism. Here, we identified two cBS siblings presenting hypokalemia in a Chinese family due to novel compound heterozygous CLCNKB mutations (c.848_850delTCT/c.1755A>G). Compound heterozygos-ity was confirmed by amplifying and sequencing the patient’s genomic DNA. The synonymous mutation c.1755A>G (Thr585Thr) was located at +2 bp from the 5′ splice donor site in exon 15. Further transcript analysis demonstrated that this single nucleotide mutation causes exclusion of exon 15 in the cDNA from the proband and his mother. Furthermore, we investigated the expression and protein trafficking change of c.848_850delTCT (∆TCT) and exon 15 deletion (∆E15) mutation in vitro. The ∆E15 mutation markedly decreased the expression of ClC-Kb and resulted in a low-molecular-weight band (~55 kDa) trapping in the endoplasmic reticulum, while the ∆TCT mutant only decreased the total and plasma membrane ClC-Kb protein expression but did not affect the subcellular localization. Finally, we studied the physiological functions of mutations by using whole cell patch-clamp and found that the ∆E15 or ∆TCT mutation decreased the current of the ClC-Kb/barttin channel. These results suggested that the compound defective mutations of the CLCNKB gene are the molecular mechanism of the two cBS siblings.