Serum uric acid (SUA) levels in humans are mainly regulated by urate transporters. Recent genome-wide association studies suggested that common variants of the human sodium-dependent phosphate cotransporter type 1 gene (NPT1/SLC17A1) influence SUA. NPT1 has been reported to mediate urate transport, but its physiologic role in regulating SUA in humans remains unclear. Furthermore, the findings of replication studies of the relationship between NPT1 variants and gout have been inconsistent. The aims of this study were to investigate the effect of NPT1 on gout and to determine its physiologic role.
Five hundred forty-five male Japanese patients with gout and 1,115 male Japanese control subjects were genotyped for rs1165196 (I269T), a common missense variant in NPT1. Analyses of the association between rs1165196 and gout were then conducted, focusing especially on renal underexcretion (RUE) gout. Immunohistochemical analysis and functional analysis using Xenopus oocytes were also performed.
Single-nucleotide polymorphism rs1165196 significantly decreased the risk of RUE gout (odds ratio 0.73, P = 0.031) but did not confer a risk for all gout (P = 0.123). The immunohistochemical analysis revealed that human NPT1 is localized to the apical membrane of the renal proximal tubule. The functional analysis using Xenopus oocyte expression systems showed that rs1165196 increases NPT1-mediated urate export.
This study showed that NPT1 is a urate exporter located in the renal proximal tubule in humans, and that its common gain-of-function variant, rs1165196, causes RUE gout, a major subtype of gout. These findings enable us to deepen our understanding of the physiologic role of NPT1 as a renal urate exporter as well as its pathophysiologic role in gout.