A Japanese Family Suffering from Familial Juvenile Hyperuricemic Nephropathy due to a Rare Mutation of the Uromodulin Gene

We report the case of a Japanese family suffering from familial juvenile hyperuricemic nephropathy (FJHN) due to a rare missense mutation of the uromodulin (UMOD) gene. An 18-year-old male presented with gout, hyperuricemia, and stage 3 chronic kidney disease. Mostly, FJHN is caused by a mutation altering the cystine residue of UMOD/Tamm-Horsfall protein. However, in the present case, a T688C mutation was identified in exon 4, resulting in amino acid substitution with arginine replacing tryptophan at position 230 (Trp230Arg). This mutation was also found in his brother and father with the same phenotype, indicating autosomal dominant inheritance. The affected amino acid was conserved in 200 healthy Japanese controls. Therefore, mutation T688C most likely causes rare structural and/or functional abnormalities in UMOD/Tamm-Horsfall protein.