Mutations in CLCN5 (Xp11.23) encoding a predominantly endosomal-bound Cl−/H+ exchanger, critically related to endosomal acidification, transepithelial transport and proximal tubule endocytosis, define Dent disease type 1.7 To date, ~200 mutations in CLCN5 have been reported in Dent disease patients,7 and account for ~50% of all cases. The gene discussed is CLCN5; the disease is Dent disease type 1.