ClC-Kb pore mutation disrupts glycosylation and triggers distal tubular remodeling.

Mutations in the CLCNKB gene (1p36), encoding a basolateral chloride channel, ClC-Kb, cause type 3 Bartter's syndrome. We identified a family with a mixed Bartter's / Gitelman's phenotype and early-onset kidney failure and employing a candidate gene approach, discovered a homozygous mutation (CLCNKB c.499G>T [p.Gly167Cys]) in exon 6 of CLCNKB in the index patient. We then validated these results with Sanger and whole exome sequencing. Compared to wild-type ClC-Kb, the Gly167Cys mutant conducted less current and impaired, complex N-linked glycosylation in vitro. We demonstrated that loss of Gly-167, rather than gain of a mutant Cys, impairs complex glycosylation but that surface expression remains intact. Moreover, Asn364 was necessary for channel function and complex glycosylation. Morphologic evaluation of human kidney biopsies revealed typical basolateral localization of mutant Gly167Cys ClC-Kb in cortical distal tubular epithelia. However, we detected attenuated expression of distal sodium transport proteins, changes in abundance of distal tubule segments, and hypokalemia-associated intracellular condensates from the index patient compared to control nephrectomy specimens. The present data establish what we believe, are novel regulatory mechanisms of ClC-Kb activity and demonstrate nephron remodeling in man, caused by mutant ClC-Kb, with implications for renal electrolyte handling, blood pressure control, and kidney disease.