Evidence for genetic heterogeneity in Dent's disease

Abstract

Background. Dent's disease (X-linked nephrolithiasis) is a proximal tubulopathy that has been consistently associated with inactivating mutations in the CLCN5 gene encoding the ClC-5 chloride channel expressed in tubular epithelial cells. Methods. We performed mutation analysis of the coding region of CLCN5 by DNA sequencing in 32 unrelated males, all of whom met the following three clinical criteria for the diagnosis of Dent's disease: (1) low-molecular-weight (LMW) proteinuria; (2) hypercalciuria; and (3) at least one of the following: nephrocalcinosis, kidney stones, renal insufficiency, hypophosphatemia, or hematuria. Results. Sixteen mutations (ten missense, four nonsense, two frameshift) were found in 19 patients. Mutations were confirmed by restriction analysis or allele-specific polymerase chain reaction (PCR), segregated with disease in the families, and were not polymorphisms. In the other 13 patients with Dent's disease, the coding sequence of CLCN5 was normal. In these 13 patients, we also sequenced two regions of the CLCN5 promoter (626 and 586 bp, respectively, 2.1 and 1 kb upstream of exon 2) containing regulatory sites [activating protein-1 (AP-1)-like, AP-4, and cyclic adenosine monophosphate (cAMP)-receptor element binding protein (CREB)] and primary and secondary transcription start sites. We found no mutations in these promoter sequences in any of the 13 patients. In one three-generation family, the absence of mutation was confirmed by sequencing in two additional affected family members, and in this family haplotype analysis excluded linkage to the region of the CLCN5 gene. There were no differences between the 19 patients with CLCN5 mutations and the 13 without mutations with regard to any clinical features of Dent's disease. Conclusion. These findings suggest that mutation in other gene(s) may be responsible for the phenotype of Dent's disease in some patients.