Hereditary renal hypouricemia. Isolated tubular defect of urate reabsorption

Progressive dystonia with optic atrophy in a Jewish-Iraqi family

The combination of progressive dystonia and optic atrophy is extremely rare and its morphological, metabolic and genetic basis is unknown. In a family of 9 children (8 males) born to consanguineous Israeli-Jewish-Iraqi parents, we identified four brothers who developed the syndrome at the end of the first decade. Patients had hemi or bilateral dystonia associated with striatal, mainly putaminal, atrophy on CT and MRI, various degrees of optic atrophy, minimal corticospinal tract involvement, normal intelligence and no peripheral nervous system or systemic abnormalities. No causative metabolic defect was identified. None of the several known mitochondrial DNA mutations associated with Leber's hereditary optic neuropathy (LHON) or with LHON with dystonia were detected. Likewise, linkage to the idiopathic torsion dystonia region on chromosome 9q34 was excluded. It is suggested that this in our patients might be due to a yet unidentified genomic, autosomal recessive mutation.

Acute renal failure after exercise in a child with renal hypouricemia

We describe a 15 year old boy with renal hypouricemia who developed acute renal failure after a school athletics meeting, accompanied by appendicitis. During acute renal failure, the highest level of uric acid was 5.0 mg/dL, creatinine 7.9 mg/dL and urea nitrogen 58.6 mg/dL. After recovery, the serum uric acid fell to 0.9 mg/dL and the fractional excretion of uric acid (FEuA) exceeded the normal range. The probenecid and pyrazinamide tests showed that the patient had a total defect of uric acid reabsorption. This case suggested that strenuous exercise could be responsible for acute renal failure in patients with renal hypouricemia.

Familial hypouricaemia due to an isolated tubular defect of urate reabsorption

Hypouricaemia due to an isolated renal tubular defect is a rare condition. Several members from an affected family are described. The propositus is a 12-year-old girl with hypouricaemia (0.7-1.1 mg/dl) and increased fractional excretion of uric acid (50%). Pyrazinamide and sulphinpyrazone tests revealed an attenuated response in this subject to both drugs. The mother and one of the propositus' two brothers have the same defect. The other brother has uric acid levels at the lower limit of normal and increased fractional excretion of uric acid. These results suggest familial hypouricaemia due to a pre-secretory reabsorptive tubular defect, transmitted by autosomal dominant inheritance.

Cholangiocarcinoma and severe renal hypouricemia: a study of the renal mechanisms

Hypouricemia in malignant neoplasms is rarely reported. We present a previously unreported case of cholangiocarcinoma associated with severe persistent hypouricemia (serum uric acid levels ranged from 0.07 to 0.08 mmol/L [1.16 to 1.40 mg/100 mL], and increased urate clearance (50.90 to 57.33 mL/min v a mean value in 20 normal subjects of 9.75 +/- 1.65 mL/min). High fractional urate clearance (Cus/Ccr = 0.50 to 0.58 v 0.09 +/- 0.01 in normals) was suppressed only slightly following pyrazinamide (PZA), to 0.29 versus 0.007, and was surprisingly enhanced by probenecid (PB) to 1.78 versus 0.63 in normals. No other renal tubular or metabolic abnormalities were detected. This previously unreported association of a high PZA-nonsuppressible urate excretion with a postprobenecid urate clearance exceeding glomerular filtration rate suggests that a combined renal tubular defect is responsible for hypouricemia. The patient described here provides evidence to support the presence of a presecretory reabsorptive defect in association with a "relatively high" urate secretion by the renal tubule. This report adds to the list of hypouricemic conditions and presents an important clue to elucidate urate handling mechanisms in man.

Uric acid metabolism in children

The renal excretion of uric acid in children differs quantitatively, and perhaps qualitatively, from that in adult humans. The younger the child, the greater the renal clearance of uric acid and the greater the excretion of uric acid expressed as mg per kg body weight. During infancy, the reduced ability to maximally concentrate the urine may protect against precipitation of uric acid crystals within the kidney. Conversely, the extremely high urinary uric concentrations places the very small infant at jeopardy during sudden increases in the filtered load of uric acid. Understanding the pharmacologic and physiologic modulators of renal uric acid clearance will allow the pediatrician to minimize the risk of uric acid nephropathy, and to understand the implications of uric acid in the serum or urine in children with fluid and electrolyte disorders. Certainly evaluation of serum and urinary uric acid concentrations is essential in any child with acute renal failure.

Hereditary renal hypouricemia in children

The renal handling of urate was investigated in four children with hereditary renal hypouricemia and in their parents. The urate/creatinine clearance ratios in the four patients were 1.02 +/- 0.28, 0.93 +/- 0.11, 1.03 +/- 0.24, and 1.46 +/- 0.26, markedly higher than those in control subjects. Except for a partial response to pyrazinamide (change in clearance ratio from 1.46 to 1.07) in one patient, pyrazinamide and benzbromarone did not affect the clearance ratios in our patients. In the parents, the urate/creatinine clearance ratios were intermediate between those of the patients and control subjects, but responses to pyrazinamide and benzbromarone were normal. These data indicate that our patients have a combined defect in renal urate reabsorption, and that one of them might be subclassified as having the hypersecretion of defect. Results also show that heterozygotes can be identified by testing their urate/creatinine clearance ratio.

Familial hyper- and hypouricemias in random and hyperlipidemic recall cohorts: the Princeton School District Family Study

Using the Princeton School Family Study, our specific aim was to estimate the prevalence of familial hyper- and hypouricemia, to estimate the proportion of probands' first-degree relatives who were similarly affected, and to evaluate the contribution of diseases, drugs, and alcohol intake (if any) to uric acid levels. We studied 379 probands and a total of 1928 subjects, 125 and 52 black probands from a randomly recalled group, 147 white and 55 black probands from a hyperlipidemic recall (top decile cholesterol and/or triglyceride) group. Familial hyper- and hypouricemias were arbitrarily identified in those kindreds having at least two first-degree relatives in the same decile as the proband, top or bottom respectively, for serum uric acid. No probands had symptomatic gout. Diseases, drugs, and alcohol intake were not consistently associated with aggregations of high and/or low uric acid levels in families, and had little relationship to uric acid levels in individuals. Of the 177 randomly recalled probands, and of the 55 black probands in hyperlipidemic recall familial hyperuricemia, with concurrent primary hyperlipoproteinemia and hypertension. Familial hypouricemia was present in 1 of 125 white and in 1 of 52 randomly recalled black kindreds, and in 3 of 147 white and 3 of 55 hyperlipidemic recall black kindreds. While familial clustering of hyperuricemia was limited, clustering of hypouricemia was much more marked. Seventy-four and 84% respectively of first-degree relatives of hypouricemic white and black probands had uric acid less than the 50th percentile. In randomly recalled probands and their first-degree relatives there were significant inverse partial correlations between uric acid and high density lipoprotein cholesterol. Inverse associations of uric acid with high density lipoprotein cholesterol and the concurrence of hyperlipoproteinemia and hypertension in hyperuricemic families points to the importance of lipoprotein and blood pressure screening in families with asymptomatic hyperuricemia. The potential ramifications of within-family clustering of hypouricemia need to be further assessed in populations, particularly in regards to uric acid nephrolithiasis.