Purine enzyme defects as a cause of acute renal failure in childhood

Novel HGPRT 293 A>G point mutation presenting as neonatal acute renal failure

We report on a rare case of hypoxanthine guanine phosphoribosyl transferase (HGPRT) deficiency that presented in the newborn period with acute renal failure (ARF). The clinical diagnosis was made on the basis of non-oliguric ARF and evidence of crystal nephropathy on renal biopsy. HGPRT deficiency was eventually confirmed by enzymatic and genetic testing, showing a novel point mutation, 293 A>G. Immediate treatment consisted of peritoneal dialysis with, initially, lactate- then bicarbonate-buffered 1.36% glucose solution together with oral administration of allopurinol. Follow-up after more than 4 years continued to show hyper-echogenic kidneys with almost normal renal glomerular function. There continues to be no neurobehavioural abnormalities.

Lesch-Nyhan syndrome presenting with acute renal failure in a 3-day-old newborn

Acute renal failure developed during the first 3 days after birth in a newborn subsequently diagnosed with hypoxanthine-guanine-phosphoribosyl-transferase (HPRT) deficiency. Fluid infusion and allopurinol therapy normalised renal function and serum uric acid levels. Only a few cases of acute renal failure due to acute hyperuricemic nephropathy related to HPRT deficiency have previously been reported in infants, and there are no reported cases in newborns as young as 3 days old.

Acute renal failure from xanthine nephropathy during management of acute leukemia

Tumor lysis syndrome is a potentially life-threatening complication of induction chemotherapy for treatment of lymphoproliferative malignancies. Serious complications of tumor lysis syndrome are rare with the preemptive use of allopurinol, rasburicase, and urine alkalinization. We report a case of oliguric acute renal failure due to bilateral xanthine nephropathy in an 11-year-old girl as a complication of tumor lysis syndrome during the treatment of T-cell acute lymphoblastic leukemia. Xanthine nephrolithiasis results from the inhibition of uric acid synthesis via allopurinol which increases plasma and urinary xanthine and hypoxanthine levels. Reports of xanthine nephrolithiasis as a cause of tumor lysis syndrome are rare in the absence of defects in the hypoxanthine-guanine phosphoribosyl transferase (HGPRT) enzyme. Xanthine nephropathy should be considered in patients who develop acute renal failure following aggressive chemotherapy with appropriate tumor lysis syndrome prophylaxis. Urine measurements for xanthine could aid in the diagnosis of patients with nephrolithiasis complicating tumor lysis syndrome. Allopurinal dosage should be reduced or discontinued if xanthine nephropathy is suspected.

Partial hypoxanthine-guanine phosphoribosyltransferase deficiency presenting as acute renal failure

Hyperuricemia and secondary urate nephropathy are uncommon in the paediatric setting outside of tumour lysis syndrome. We describe the case of a 12-year-old boy who presented at 3 years of age with acute renal failure. The cause of this remained unknown until the development of uric acid renal calculi 9 years later. This, and the availability of the previously unknown family history, provided the subsequent diagnosis of partial hypoxanthine-guanine phosphoribosyltransferase (HPRT) deficiency. Detailed family history is important for early detection of this heterogeneous group of disorders. Early treatment may minimise long-term renal morbidity and mortality from renal insufficiency.

Eighteen-year follow-up of a patient with partial hypoxanthine phosphoribosyltransferase deficiency and a new mutation

Hypoxanthine phosphoribosyltransferase (HPRT) deficiency is an inherited disorder. Complete deficiency of HPRT activity is phenotypically expressed as the devastating Lesch-Nyhan syndrome. Partial HPRT deficiency usually causes hyperuricemia, precocious gout, and uric acid nephrolithiasis. We describe an 18-year follow-up of a 5-year old boy with partial HPRT deficiency and report a novel mutation in his HPRT gene. He presented with overproduction of uric acid and passage of uric acid renal stones, and without gout or neurological and behavioral abnormalities. Treatment with allopurinol, adequate hydration, urinary alkalization, and a low-purine diet was started. No subsequent nephrolithiasis has occurred. After 18-year of this therapy his physical and neuropsychological status were normal, merely his glomerular filtration rate (GFR, normal 97-137 mL min(-1)/1.73 m(2)) fell from normal to 65.1 mL min(-1). The most likely cause of initial renal impairment in our patient is uric and/or xanthine crystalluria. A missense and transition mutation 169A>G (57ATG>GTG, 57met>val) in exon 3 of the patient's HPRT gene was identified and the mother was the carrier of the mutation. As far as we are aware, the identified mutation has not previously been reported. We named the mutant HPRT Maribor.

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.

Childhood hyperuricemia and acute renal failure resulting from a missense mutation in the HPRT gene

A 6-year-old boy was determined to have partial hypoxanthine phosphoribosyl transferase (HPRT) enzyme deficiency without the phenotypic features of Lesch-Nyhan syndrome. He presented with recurrent acute renal failure (ARF) from hyperuricemia. Treatment with allopurinol prevented further attacks of renal failure. T lymphocyte cultures were used to sequence the HPRT cDNA and a novel single nucleotide substitution at codon 65 in exon 3 was found (193C>T, 65leu>phe). This mutation was confirmed by genomic DNA sequencing and was also detected in his heterozygous, asymptomatic mother and sister. Unlike the cells from patients with classic Lesch-Nyhan syndrome, the in vitro cultures of our patient's T-lymphocytes did not proliferate in the presence of purine analogue 6-thioguanine (TG). This report highlights the unusual occurrence of recurrent ARF in a child with partial HPRT enzyme deficiency. The absence of TG resistance in vitro with this mutation shows that even small alterations in enzyme activity in vivo can result in disease symptoms, in this instance, hyperuricemia sufficient to cause ARF. Atypical HPRT mutations should also be considered in cases of unusual renal failure, because correct diagnosis can allow appropriate treatment, as well as informed genetic counseling.

Acute renal failure due to xanthine stones

A 9-month-old child with the skeletal abnormalities of Fuhrmann's syndrome presented with acute renal failure secondary to bilateral renal calculi. Hereditary xanthinuria was shown to be the underlying metabolic defect. Treatment with allopurinol was unsuccessful at reducing the xanthine excretion.

When and how does one search for inborn errors of purine and pyrimidine metabolism?

Disorders in purine and pyrimidine metabolism may be difficult to recognize because their recent description means many are little known. They cover a broad spectrum of illnesses, can present from birth to the 80s, have multiple symptoms and lead to early death. Recognition of new disorders requires skill and serendipity. Often parents of affected children provide valuable clues. These disorders should be suspected, particularly where the history involves siblings, in anaemia, susceptibility to infection, or neurological deficits including autism, delayed development, epilepsy, self-mutilation, muscle weakness and - unusual in children and adolescents - gout. Some patients present with kidney stones, renal failure, alone or with the above, or as an intolerance/sensitivity to therapy (fluorouracil or azathioprine immunosuppression). These disorders can be detected from the abnormal metabolites in body fluids and/or altered enzyme activity. Abnormal cellular nucleotides or renal clearance may sometimes provide the only clue. Diagnosis can be difficult because of genetic heterogeneity and interference by blood transfusion, diet or drugs. Tests incorporating enzyme peak shifts and online diode-array detection are essential. Collaborative research is needed to improve the diagnosis and understanding of the metabolic basis for these sometimes devastating disorders and to apply this knowledge to the more common killers of mankind.

Partial hypoxanthine-guanine phosphoribosyl transferase deficiency in two Korean siblings--a new mutation

Two Korean siblings with partial hypoxanthine-guanine phosphoribosyltransferase (HPRT) deficiency are reported. The index patient was a boy aged 9 years 10 months who developed acute renal failure with a serum uric acid level of 25.9 mg/dl, after vomiting. The younger brother was asymptomatic but had elevated serum uric acid (9.4 mg/dl). The red blood cell HPRT activity of both siblings was one-tenth of normal. Analysis of genomic DNA revealed a point mutation from A (adenine) to G (guanine) at nucleotide position 215 on exon 3; this is a new mutation. The younger brother had the same mutation and the mother was heterozygous for this mutation.

Gout, uric acid and purine metabolism in paediatric nephrology

Although gout and hyperuricaemia are usually thought of as conditions of indulgent male middle age, in addition to the well-known uricosuria of the newborn, there is much of importance for the paediatric nephrologist in this field. Children and infants may present chronically with stones or acutely with renal failure from crystal nephropathy, as a result of inherited deficiencies of the purine salvage enzymes hypoxanthine-guanine phosphoribosyltransferase (HPRT) and adenine phosphoribosyltransferase (APRT) or of the catabolic enzyme xanthine dehydrogenase (XDH). Genetic purine overproduction in phosphoribosylpyrophosphate synthetase superactivity, or secondary to glycogen storage disease, can also present in infancy with renal complications. Children with APRT deficiency may be difficult to distinguish from those with HPRT deficiency because the insoluble product excreted, 2,8-dihydroxyadenine (2,8-DHA), is chemically very similar to uric acid. Moreover, because of the high uric acid clearance prior to puberty, hyperuricosuria rather than hyperuricaemia may provide the only clue to purine overproduction in childhood. Hyperuricaemic renal failure may be seen also in treated childhood leukaemia and lymphoma, and iatrogenic xanthine nephropathy is a potential complication of allopurinol therapy in these conditions. The latter is also an under-recognised complication of treatment in the Lesch-Nyhan syndrome or partial HPRT deficiency. The possibility of renal complications in these three situations is enhanced by infection, the use of uricosuric antibiotics and dehydration consequent upon fever, vomiting or diarrhoea. Disorders of urate transport in the renal tubule may also present in childhood. A kindred with X-linked hereditary nephrolithiasis, renal urate wasting and renal failure has been identified, but in general, the various rare types of net tubular wasting of urate into the urine are recessive and relatively benign, being found incidentally or presenting as colic from crystalluria. However, the opposite condition of a dominantly inherited increase in net urate reabsorption is far from benign, presenting as familial renal failure, with hyperuricaemia either preceding renal dysfunction or disproportionate to it. Paediatricians need to be aware of the lower plasma urate concentrations in children compared with adults when assessing plasma urate concentrations in childhood and infancy, so that early hyperuricosuria is not missed. This is of importance because most of the conditions mentioned above can be treated successfully using carefully controlled doses of allopurinol or means to render urate more soluble in the urine. Xanthine and 2,8-DHA are extremely insoluble at any pH. Whilst 2,8-DHA formation can also be controlled by allopurinol, alkali is contraindicated. A high fluid, low purine intake is the only possible therapy for XDH deficiency.

Erythrocyte nucleotide stability and plasma hypoxanthine concentrations: improved ATP stability with short-term storage at room temperature

We have measured erythrocyte nucleotide concentrations at timed intervals over 24 h in heparinised blood stored at 4 degrees C, room temperature, or 37 degrees C. The objective was to determine whether the grossly altered NAD concentrations found in the erythrocytes of patients with two different inherited purine disorders could be related to altered stability or turnover rates. An unexpected finding was the improved stability of all erythrocyte nucleotides in blood stored at room temperature compared with 4 degrees C. Not only was the breakdown of ATP greater at 4 degrees C compared with room temperature, higher hypoxanthine concentrations were present in the plasma associated with a fictitious increment in inosine. NAD and NADP, by contrast, showed remarkable stability in both control and patient erythrocytes, irrespective of their original value. Although these studies failed to establish an explanation for the altered NAD levels in the patients, the superior ATP stability in blood stored at room temperature in the erythrocytes from both patients and controls suggests that current practices of storing blood on ice for short-term studies require re-evaluation.