Clinical and genetic studies of CLCN5 mutations in Japanese families with Dent's disease

Background. Dent's disease is an X-linked renal tubular disorder that is ch aracterized by low molecular weight protein-uria. hypercalciuria, nephrolit hiasis, and renal failure. The disease is caused by inactivation of a renal chloride channel gene, CLCN5. that encodes a 746-amino acid protein with 1 2 to 13 transmembrane domains. The Japanese variant of Dent's disease has b een observed to be less severe. and we have investigated two unrelated Japa nese families for CLCN5 mutations. Methods. Six patients from two unrelated families were studied. Leukocyte D NA from probands was used with CLCN5-specific primers for polymerase chain reaction (PCR) amplification of the coding region and exon-intron boundarie s, and the DNA sequences of the products were determined to identify abnorm alities in the gene. RNA extracted from the kidney, leukocytes, or urine se diments was used to characterize further the effects of the identified muta tions. Results. beta(2)-microglobulinuria was detected in five patients, hypercalc iuria in two patients, nephrolithiasis in three patients (2 of whom were fe males), and one 51-year-old man had renal failure. Two novel CLCN5 mutation s consisting, of an a to g transition at the invariant ag acceptor splice s ite of intron 5 and an intragenic deletion that encompassed the region betw een intron 3 and intron 6 were identified. The acceptor splice site mutatio n led to the utilization of two alternative cryptic splice sites in exon 6 that resulted in a frameshift or skipping of the exon 6. The deletional mut ation. which resulted in a loss of exons ii, 5, and 6. is predicted to lead to a loss of domains 1 through 4. Both mutations predict truncated chlorid e channels that are likely to result in a functional loss. Conclusions. The observations of renal failure in one male and nephrolithia sis in two females represent important new findings in this Japanese varian t of Dent's disease that is associated with CLCN5 mutations. In addition, o ur study is the first to demonstrate the use of urinary sediment cells and renal tissue for the detection of CLCN5 transcript abnormalities. These res ults help to expand the spectrum of CLCN5 mutations associated with Dent's disease.