Rapid detection of R90H mutations in the human urate transporter 1 gene

Allele-specific real-time polymerase chain reaction as a tool for urate transporter 1 mutation detection

Allele-specific polymerase chain reaction (ASPCR) method has long been applied for the detection of nucleotide variations and genotyping, which are detected by the presence or absence of DNA amplification PCR products. Recently, Real-Time PCR genotyping has fast developed and offered a rapid method of detecting mutations without the need of gel electrophoresis as with ASPCR. Here, we describe an easy and rapid touchdown real-time PCR method for the detection of nucleotide variations. Using our method we successfully detect two main mutations in human urate transporter 1 (SLC22A12), W258X and R90H, and validate the results. The method can potentially be applied to genotype of various other nucleotide variations.

Simple and rapid detection method for the mutations in SLC22A12 that cause hypouricemia by allele-specific real-time polymerase chain reaction

BACKGROUND

Hypouricemia is a disorder that serum urate level is less than 2.0 mg/dl, and relatively common in the Japanese population, where the main genetic cause of hypouricemia is W258X and R90H mutations in human urate trasnsporter 1(SLC22A12). Small scale screening has relied on time-consuming traditional ways like polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Therefore, it is beneficial that we have an easy and rapid detection method for these mutations.

METHODS

In this report, we established a touchdown allele-specific real-time polymerase chain reaction (ASPCR) assay for detecting W258X and R90H mutations in SLC22A12, respectively.

RESULTS

Quantifiable discrimination was successfully achieved by ∆Ct value. Furthermore, we conducted W258X and R90H screening against 120 control genome sets, whereby frequency was 2.92% for W258X, and not detected for R90H, respectively.

CONCLUSIONS

The two mutations, W258X and R90H in SLC22A12 were successfully genotyped by an easy and rapid ASPCR assay.

Uricosuric action of losartan via the inhibition of urate transporter 1 (URAT 1) in hypertensive patients

BACKGROUND

The angiotensin receptor blocker losartan inhibited urate transporter 1 (URAT1) according to in vitro experiments. However, it is still unknown whether the inhibitory effect of losartan on URAT1 contributes to its uricosuric action in humans.

METHODS

Thirty-two patients with hypertension and nine patients with idiopathic renal hypouricemia (five with and four without hypertension) were enrolled for this study. Hypertensive patients were prescribed oral losartan (50 mg/day, n = 16) or candesartan (8 mg/day, n = 16). Before and after 1-month treatment, the serum concentration of urate (Sur) and creatinine (Scr), and the clearance value of urate (Cur) and creatinine (Ccr) were determined. Clearance studies using the URAT1 inhibitor benzbromarone (100 mg/day) or losartan (50 mg/day) loading test were also performed in these patients.

RESULTS

Blood pressure (BP) significantly decreased in the patients treated with either losartan or candesartan. Losartan significantly reduced Sur, which was associated with a concomitant increase in the Cur/Ccr ratio, whereas candesartan did not alter these parameters. In hypertensive patients with loss-of-function mutation of URAT1, losartan did not alter either Sur or Cur/Ccr, nor did benzbromarone. The lack of effect of URAT1 inhibitors on renal excretion of urate was independent of the renal function of hypouricemic patients. On the other hand, both losartan and benzbromarone increased Cur/Ccr ratio in hypertensive patients harboring the wild URAT1 gene, regardless of the presence of hypouricemia.

CONCLUSIONS

These findings suggested that losartan inhibited URAT1 and thereby it lowered Sur levels in hypertensive patients.