CHARACTERIZATION OF RENAL CHLORIDE CHANNEL, CLCN5, MUTATIONS IN HYPERCALCIURIC NEPHROLITHIASIS (KIDNEY-STONES) DISORDERS

Mutations of the renal-specific chloride channel (CLCN5) gene, which i s located on chromosome Xp11.22, are associated with hypercalciuric ne phrolithiasis (kidney stones) in the Northern European and Japanese po pulations. CLCN5 encodes a 746 amino acid channel (CLC-5) that has sim ilar to 12 transmembrane domains, and heterologous expression of wild- type CLC-5 in Xenopus oocytes has yielded outwardly rectifying chlorid e currents that were markedly reduced or abolished by these mutations. In order to assess further the structural and functional relationship s of this recently cloned chloride channel, additional CLCN5 mutations have been identified in five unrelated families with this disorder. T hree of these mutations were missense (G57V, G512R and E527D), one was a nonsense (R648Stop) and one was an insertion (30:H insertion). In a ddition, two of the mutations (30:H insertion and E527D) were demonstr ated to be de novo, and the G57V and E527D mutations were identified i n families of Afro-American and Indian origin, respectively. The G57V and 30:H insertion mutations represent the first CLCN5 mutations to be identified in the N-terminus region, and the R648Stop mutation, which has been observed previously in an unrelated family, suggests that th is codon may be particularly prone to mutations. Heterologous expressi on of the mutations resulted in a marked reduction or abolition of the chloride currents, thereby establishing their functional importance. These results help to elucidate further the structure-function relatio nships of this renal chloride channel.