A novel mutation in the uromodulin gene in a Japanese family with a mild phenotype of familial juvenile hyperuricemic nephropathy

Familial juvenile hyperuricemic nephropathy (FJHN) is an autosomal-dominant disorder that is characterized by hyperuricemia and chronic renal failure and results in end-stage renal failure. FJHN is caused by mutations in the UMOD gene, which encodes uromodulin. Uromodulin contains three epidermal growth factor (EGF)-like domains, a domain of eight cysteine residues (D8C), and a zona pellucid-like domain. Over 90 % of UMOD mutations are missense mutations, and over 80 % exist in exon 4, which encodes both D8C and the EGF-like domains. A 56-year-old woman was diagnosed with hyperuricemia with a serum uric acid level of 7.5 mg/dL, and stage III chronic kidney disease (CKD) with a serum creatinine level of 1.12 mg/dL and an estimated glomerular filtration rate of 39.9 mL/(min 1.73 m2). The patient had a family history of hyperuricemia and stage IV CKD; both the patient and her affected family members had a novel mutation in the UMOD gene: c.C518G (p.P173R), located between the EGF-like domains and D8C. This mutation, along with previously reported nearby mutations, causes a clinically mild phenotype of FJHN. It is important that physicians consider the diagnosis of FJHN in patients with a family history of hyperuricemia associated with renal dysfunction, even if the patient has only mild renal impairment.