Renal handling of urate in a patient with familial juvenile gouty nephropathy

Effect of Pyrazinamide and Probenecid on Peritoneal Urate Transport Kinetics during Continuous Ambulatory Peritoneal Dialysis

Objective

We administered pyrazinamide (PZA) and probenecid (PB) — two well-known modulators of urate transport via the proximal tubules — to evaluate their impact on urate transport through the peritoneal membrane and to clarify mechanisms affecting peritoneal transport.

Setting

A continuous ambulatory peritoneal dialysis (CAPD) unit in 2nd Hospital of IKA (Social Services Institute), Greece.

Patients

In 20 stable CAPD patients, on the study day, a 4-hour, 2-L, 1.36% glucose exchange was performed (control exchange). Pyrazinamide 3 g was given orally and another identical exchange was performed (study exchange). The same protocol was repeated with 2 g PB. Kt/V, peritoneal clearances of urea, creatinine, and urate for each exchange, and mass transfer area coefficients (MTAC) for the three solutes and their dialysate-to-plasma concentration (D/P) ratios were used to estimate peritoneal transport.

Results

Administration of PZA resulted in decreased clearances and MTAC values for the three solutes. The D/P ratio decreased significantly only for urate, indicating a more intense influence of PZA on urate. After PB administration, clearances of urea, creatinine, and urate were increased. MTAC and D/P ratio increased significantly only for urate ( p < 0.05), demonstrating an action similar to that exerted on renal tubules.

Conclusions

These findings provide evidence that unrestricted diffusion is not the only transport mechanism in the case of urate, and demonstrate the existence of an active mechanism in peritoneal urate transport with a reabsorptive and, probably, a secretive component that resembles that of renal tubule urate transport. Attention should be given in the case of CAPD patients undergoing antituberculous (PZA) treatment: it might have a negative impact on urea, creatinine, and urate peritoneal transport rates.

Tophus gout and chronic kidney disease in a young female patient: report of familial juvenile hyperuricemic nephropathy in three generations of the same family

A 20-year-old female was admitted with tophus gout and chronic kidney disease (CKD), progressing to dialysis need and death. The familial investigation evidenced several cases of hyperuricemia, gout and CKD, as well as several cases of early death due to CKD. After analyzing these cases, it was concluded that the diagnosis was familial juvenile hyperuricemic nephropathy. This is an autosomal dominant disorder caused by mutations in the uromodulin gene, characterized by early beginning hyperuricemia and gout, in men and women, associated with progressive CKD.

Hereditary hyperuricemia and renal disease

Hyperuricemia and gout have long been known to run in families. As well as an apparently multifactorial genetic component to classic gout itself, 2 rather unusual sex-linked single-gene disorders of purine biosynthesis or recycling have been defined: deficiency of the enzyme hypoxanthine-guaninephosphoribosyl transferase (HPRT), and overactivity of PPriboseP synthase. Both result in overproduction of urate, hyperuricemia, and secondary overexcretion that may lead to acute or chronic renal damage. Familial juvenile hyperuricemic nephropathy (FJHN) and autosomal-dominant medullary cystic kidney disease (ADMCKD) are more common but less well-defined hyperuricemic conditions resulting from a decrease in the fractional excretion of filtered urate, with normal urate production. Although having features in common, ADMCKD is distinguished in particular by the presence of medullary cysts. One major group of both disorders is associated with mutations in the gene for uromodulin, but this accounts for only about one third of cases, and genetic heterogeneity is present. Whether the genes involved in these latter disorders contribute to the polygenic hyperuricemia and urate underexcretion of classic gout remains unexplored.