Characterisation of renal chloride channel, CLCN5, mutations in hypercalciuric nephrolithiasis (kidney stones) disorders

Mutations of the renal-specific chloride channel (CLCN5) gene, which islocated on chromosome Xp11.22, are associated with hypercalciuricnephrolithiasis (kidney stones) in the Northern European and Japanesepopulations. CLCN5 encodes a 746 amino acid channel (CLC-5) that hasapproximately 12 transmembrane domains, and heterologous expression ofwild-type CLC-5 in Xenopus oocytes has yielded outwardly rectifyingchloride currents that were markedly reduced or abolished by thesemutations. In order to assess further the structural and functionalrelationships of this recently cloned chloride channel, additional CLCN5mutations have been identified in five unrelated families with thisdisorder. Three of these mutations were missense (G57V, G512R and E527D),one was a nonsense (R648Stop) and one was an insertion (30:H insertion). Inaddition, two of the mutations (30:H insertion and E527D) were demonstratedto be de novo, and the G57V and E527D mutations were identified in familiesof Afro-American and Indian origin, respectively. The G57V and 30:Hinsertion mutations represent the first CLCN5 mutations to be identified inthe N-terminus region, and the R648Stop mutation, which has been observedpreviously in an unrelated family, suggests that this codon may beparticularly prone to mutations. Heterologous expression of the mutationsresulted in a marked reduction or abolition of the chloride currents,thereby establishing their functional importance. These results help toelucidate further the structure-function relationships of this renalchloride channel.