Abstract:
Citrate plays an important role in the prevention of renal stone formation. Hypocitraturia is a major metabolic stone risk factor in Thai renal stone patients. Regards that citrate is reabsorbed at renal proximal tubules via sodium-dicarboxylate cotransporter-1 (NaDC-1), NaDC-1 activity is important for urinary citrate regulation. A previous study in a Japanese population suggested that a polymorphism, rs11567842, in NaDC-1 gene was associated with hypocitraturic phenotype in recurrent kidney stone formers. We, here, investigated the sequence variations of NaDC-1 and evaluated the association of its variations with the urinary citrate, potassium, magnesium, calcium and sodium levels in Thai renal stone patients. In this study, 158 Thai renal stone patients (aged 23-82 years old, 68.4% males) visited the Urology Clinic, Sunpasit Prasong Hospital, Ubon Ratchathani province were recruited. Blood and 24 hours urine were collected. The leukocyte genomic DNA was extracted and the sequence variation of NaDC-1 was determined by PCR-sequencing. Urine parameter associated with stone formation including creatinine, citrate, potassium, magnesium, sodium, and calcium were measured using standard methods. PCR-sequencing the entire coding regions of NaDC-1 identified only one polymorphism, rs11567842 (c.1716A>G; p.I550V) located in exon 12. The frequencies of the A and G alleles were 0.73 and 0.27, respectively. Of all 158 subjects, the AA, AG and GG genotypes were 51.9%, 41.8% and 6.3%, respectively. Kidney stone patients with GG genotype had higher urinary citrate levels than AA (wild-type) genotype (158.41 vs 61.88 mg/gCr). Moreover, patients with GG genotype also had higher levels of urinary potassium, magnesium, calcium and sodium excretions. The AA genotype in renal stone patients was significantly associated with the hypocitraturic phenotype (P = 0.018). In conclusion, the SNP rs11567842 (c.1716A>G) of NaDC-1 gene was associated with citraturia in Thai patients with renal stones.