Complete deficiency of adenine phosphoribosyltransferase: a third case presenting as renal stones in a young child

APRT deficiency: the need for early diagnosis

Adenine phosphoribosyltransferase (APRT) deficiency is a rare autosomal recessive disorder which leads to accumulation of poorly soluble 2,8-dihydroxyadenine in kidneys resulting in nephrolithiasis as well as chronic kidney disease from crystal nephropathy. This report describes a 55-year-old previously fit man who presented with shortness of breath and the investigative pathway that eventually led to a diagnosis of APRT deficiency. Early diagnosis has aided in timely institution of allopurinol, thereby improving his renal function and possibility of weaning off renal replacement therapy. Genetic testing has enabled early identification of other family members at risk and prevention of renal failure by commencing xanthine oxidoreductase (XOR) inhibitors. The issues surrounding kidney donation by a member of this family are also discussed. This case represents the importance of awareness and recognition of the signs and symptoms of this rare condition, complications of which can be easily prevented by early institution of XOR inhibitor therapy.

2,8-Dihydroxyadenine urolithiasis: a not so rare inborn error of purine metabolism

Adenine phosphoribosyltransferase (APRT) deficiency is a rare inherited metabolic disorder that leads to the formation and hyperexcretion of 2,8-dihydroxyadenine (DHA) into urine. The low solubility of DHA results in precipitation and formation of urinary crystals and kidney stones. The disease can be present as recurrent urolithiasis or nephropathy secondary to crystal precipitation into renal parenchyma (DHA nephropathy). The diagnostic tools available, including stone analysis, crystalluria, and APRT activity in red blood cells, make the diagnosis easy to confirm when APRT deficiency is suspected. However, the lack of recognition of this metabolic disorder frequently resulted in a delay in diagnosis and treatment with grave consequences. The early recognition and treatment of APRT deficiency are of crucial importance to prevent irreversible loss of renal function. This review summarizes the genetic and metabolic mechanisms underlying DHA stones formation and chronic kidney disease, along with the issues of diagnosis and management of APRT deficiency. Moreover, we report the mutations in the APRT gene responsible for APRT deficiency in 51 French patients (43 families) including 22 pediatric cases (18 families) among the 64 patients identified in the biochemistry laboratories of Necker Hospital, Paris (1978-2013).

Adenine phosphoribosyltransferase deficiency: Leave no stone unturned

Adenine phosphoribosyltransferase (APRT) deficiency is a rare autosomal recessive disease leading to generation of large amounts of 2,8-dihydroxyadenine (DHA). DHA is excreted in urine, where it precipitates into crystals due to its low solubility. DHA crystals can aggregate into stones or cause injury to the renal parenchyma (DHA nephropathy). Recurrent urolithiasis and DHA nephropathy are the two clinical manifestations of APRT deficiency. Diagnosis of APRT deficiency can be made during childhood as well as adulthood. Diagnosis mainly relies on the recognition of DHA in stones or urine crystals. Measurement of APRT activity and genetic testing are useful for confirmation of diagnosis, for family screening and should be considered in difficult cases of urolithiasis or crystalline nephropathy. Allopurinol therapy is the cornerstone of treatment and is highly effective in preventing recurrence of stones and kidney disease. High fluid intake and dietary modifications are also recommended. Early diagnosis and treatment are of paramount importance to prevent renal damage. Unfortunately, diagnosis of APRT deficiency is often overlooked and irreversible renal failure still occurs in a substantial proportion of patients. Clinicians must be alert to the possibility of APRT deficiency and consider the appropriate diagnostic tests in certain cases. This review discusses the genetic and biochemical mechanisms of APRT deficiency, and the issues of diagnosis and management.

Adenine phosphoribosyltransferase deficiency

Complete adenine phosphoribosyltransferase (APRT) deficiency is a rare inherited metabolic disorder that leads to the formation and hyperexcretion of 2,8-dihydroxyadenine (DHA) into urine. The low solubility of DHA results in precipitation of this compound and the formation of urinary crystals and stones. The disease can present as recurrent urolithiasis or nephropathy secondary to crystal precipitation into renal parenchyma (DHA nephropathy). The diagnostic tools available-including stone analysis, crystalluria, and APRT activity measurement-make the diagnosis easy to confirm when APRT deficiency is suspected. However, the disease can present at any age, and the variability of symptoms can present a diagnostic challenge to many physicians. The early recognition and treatment of APRT deficiency are of crucial importance for preventing irreversible loss of renal function, which still occurs in a non-negligible proportion of cases. This review summarizes the genetic and metabolic mechanisms underlying stone formation and renal disease, along with the diagnosis and management of APRT deficiency.

Adenine phosphoribosyltransferase deficiency in children

Adenine phosphoribosyltransferase (APRT) deficiency is a rare autosomal recessive disorder characterized by 2,8-dihydroxyadenine (2,8-DHA) crystalluria that can cause nephrolithiasis and chronic kidney disease. The aim of our study was to assess the clinical presentation, diagnosis, and outcome of APRT deficiency in a large pediatric cohort. All pediatric cases of APRT deficiency confirmed at the same French reference laboratories between 1978 and 2010 were retrospectively reviewed. Twenty-one patients from 18 families were identified. The median age at diagnosis was 3 years. Diagnosis was made after one or more episodes of nephrolithiasis (17 patients), after urinary tract infection (1 patient), and by family screening (3 patients). The diagnosis was based on stone analysis and microscopic examination of urine and/or enzymatic determination of APRT on red blood cells. All children had null APRT enzyme activity in erythrocytes. APRT gene sequencing was performed on 18 patients, revealing six homozygous and 12 compound heterozygous mutations. At diagnosis, half of the patients had decreased kidney function, and two children presented with acute renal failure. Allopurinol treatment was given to all patients at a median dose of 9 mg/kg/day. After a median follow-up of 5 years, all patients showed stabilization or improvement of kidney function, normal growth and development, and six patients had recurrence of nephrolithiasis. Based on these results, we conclude that an excellent outcome can be achieved in children with APRT deficiency who receive the proper treatment.

Adenine phosphoribosyltransferase deficiency in Iceland

Two children and two adults of four unrelated families were on regular light microscopic examination found to exhibit identical, spherical urine crystals. Their characteristic appearance led to the diagnosis of 2,8-dihydroxyadenine crystalluria by spectrophotometric or gas-chromatographic/mass-spectrometric analysis. Total deficiency of adenine phosphoribosyltransferase was confirmed by direct measurements of the enzyme activity in lysed red blood cells. Close family members were also examined for the enzyme defect, revealing no additional homozygotes, but 13 heterozygotes among 14 relatives. We suggest that round, brownish urine crystals, even without radiolucent kidney stones, should alert the physician to search for the existence of 2,8-dihydroxyadenine. Proper treatment could then be instituted without delay, preventing eventual kidney damage.

Genetic disorders and urolithiasis

A recent analysis of the McKusick's On-Line Mendelian Inheritance in Man (OMIM) database revealed over 30 genetic or putatively genetic conditions in which urolithiasis contributes to the disease pathology at least to some extent. There is wide clinical, biochemical, and genetic heterogeneity in many of these conditions.

Analysis of germline and in vivo somatic mutations in the human adenine phosphoribosyltransferase gene: mutational hot spots at the intron 4 splice donor site and at codon 87

We have characterized 18 germline and 10 in vivo somatic mutations in the human adenine phosphoribosyltransferase (APRT) gene. Both germline and in vivo somatic mutations were clustered at the intron 4 splice donor site and at codon 87. In vitro somatic mutations in human APRT do not appear to show this clustering. These findings suggest that the spectrum of germline mutations in APRT may be similar to that incurred by somatic cells in vivo, but different from that seen in cultured cells. Thus, in vivo, rather than in vitro, somatic mutations in this gene may be more representative of mutational events occurring in the germline.

Renal insufficiency secondary to 2,8-dihydroxyadenine urolithiasis

A 48-year-old man with a history of recurrent urolithiasis and chronic renal failure underwent a nephrectomy for a renal mass. At surgery the mass proved to be a calculus impacted in a dilated calyx. Gross examination of the kidney revealed chalky white deposits in the deep medulla and papillary tips. Histologic examination revealed chronic interstitial nephritis with brown spicules within some tubular epithelial cells and larger deposits of brown crystals within tubular lumina, the interstitium of the medulla, and papillary tips. Polarization microscopy revealed individual crystals scattered throughout the renal parenchyma. Although the arrangement of the crystals was reminiscent of uric acid, and, in fact, a clinical diagnosis of gouty nephropathy was made, x-ray diffraction analysis demonstrated crystals of 2,8-dihydroxyadenine. Enzymatic studies confirmed the complete absence of adenine phosphoribosyltransferase activity in erythrocyte lysates.

Disturbance in the metabolism of 5'-methylthioadenosine and adenine in patients with neoplastic diseases, and in those with a deficiency in adenine phosphoribosyltransferase

5'-Methylthioadenosine (MTA) produced during the synthesis of polyamines is degraded to adenine by MTA phosphorylase. This pathway is considered to be the main source of endogenous adenine. We determined the concentrations of MTA and adenine in control subjects and in those with a pathological disorder. In patients with active leukemias, as well as with other types of malignancies, the concentrations of MTA and adenine in the urine were elevated. These changes seemed to be the result of an accelerated production of MTA due to an accelerated biosynthesis of polyamine. In patients with adenine phosphoribosyltransferase (APRT) deficiency, the concentrations of adenine in the urine were elevated, presumably due to a disturbance in the catabolism of adenine. Although adenine is a potent inhibitor of MTA phosphorylase, APRT-deficient patients did not excrete MTA into urine in concentrations significantly larger than noted for control subjects. However, the amount of MTA excreted positively correlated with that of adenine in these patients, hence that accumulated adenine probably had a slight, but positive, inhibitory effect on the degradation of MTA.

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

Acute renal failure (ARF) is not listed as a usual form of presentation in hypoxanthine-guanine phosphoribosyltransferase deficiency, despite the gross uric acid overproduction in the defect. We found that a third of such patients may present in ARF when the urinary uric acid/creatinine ratio may be normal, not raised, and the defect may be suspected from the disproportionate increase in plasma uric acid. This is important in view of the potential confusion of uric acid with 2,8-dihydroxyadenine, the even more insoluble purine excreted in the other salvage enzyme disorder, adenine phosphoribosyltransferase deficiency. In that disorder, presentation in ARF is well recognized, the uric acid/creatinine ratio is also normal, but plasma urate is not raised. Our combined experience in these two disorders underlines the importance of early recognition and treatment with carefully adjusted doses of allopurinol, which may reverse or postpone renal failure.

2,8-Dihydroxyadenine urolithiasis: report of a case in a woman in the United States

Disorders of purine metabolism are well recognized clinical entities in modern medical practice. However, there are lesser known aberrations of purine and pyrimidine metabolism that can manifest as disease states. Deficiency of the enzyme adenine phosphoribosyltransferase is an autosomal recessive inherited disorder resulting in 2,8-dihydroxyadenuria, and possible urolithiasis and renal insufficiency. A woman with a pure 2,8-dihydroxyadenine ureteral calculus is reported, who represents the third reported case in the United States. Stones comprised of 2,8-dihydroxyadenine are difficult to distinguish from uric acid clinically, making sophisticated crystallographic analysis essential for accurate diagnosis. Treatment differs from that appropriate for uric acid lithiasis due to the limited solubility of 2,8-dihydroxyadenine at pH levels of less than 9. Prevention requires purine restriction and allopurinol.

Urolithiasis in children: current medical management

The mechanism of stone formation in the urinary tract is reviewed. Diet, urinary tract infection and metabolic disorders account for the different epidemiological patterns of stone formation. The diagnosis and management of renal tract calculi are discussed. Calcium stones are associated with hypercalciuria, urine acidification defects, the use of furosemide in premature babies, hypercalcaemia, hyperoxaluria, hyperuricosuria, an alkaline urine and hypocitraturia. Uric acid stones occur in acid urine, from increased purine synthesis with lympho- or myeloproliferative disorders or from several inborn errors of purine metabolism which can also cause xanthine or dihydroxyadenine stones. Cystinuria, inherited as an autosomal recessive disorder is best treated with a low sodium diet, a fluid intake exceeding 40 ml/kg per day maintaining urine pH between 7.5 and 8 and, if necessary, with oral penicillamine. Oxalate stones occur in relation to diet, bowel disease and primary inherited defects in oxalate metabolism. Urinary tract infection causing struvite and carbonate apatite formation is the commonest cause of stones in Europe.

2,8-Dihydroxyadenine urolithiasis: report of an adult case in the United States

2,8-Dihydroxyadeninuria is a rare purine metabolic disorder that has been reported to have caused urolithiasis in 14 cases, mostly children. Excretion of the hydroxylated metabolites of adenine results from a deficiency of adenine phosphoribosyltransferase. The insoluble calculi have a similar chemical structure to uric acid and frequently are misdiagnosed as uric acid calculi. Management differs from that of uric acid urolithiasis. We report on an adult with 2,8-dihydroxyadenine urolithiasis in the United States.

Inhibition by adenine of in vitro immunological functions of normal and adenine phosphoribosyltransferase-deficient human lymphocytes

Exogenous adenine strongly inhibited mitogen-stimulated transformation, cytoplasmic immunoglobulin production, and natural killer activity of human mononuclear leukocytes at the high concentration of 1.0 mM. These inhibitions by adenine were not due to cytotoxicity, because the viability of cultured cells was not affected by adenine up to 1.0 mM. As the magnitude of inhibition by adenine of these in vitro immunological functions was similar in normal and adenine phosphoribosyltransferase-deficient cells, its inhibition was not mediated by corresponding nucleotides. Adenine at the concentration of 0.1 mM caused 50% inhibition of cytoplasmic immunoglobulin production without alternating cell proliferation or viability. This suggests that an appropriate concentration of adenine may inhibit the differentiation of B cells to plasma cells rather than affecting cell proliferation. Understanding the mechanisms of adenine inhibition may lead to new approaches for the regulation of immune responses.

Common characteristics of mutant adenine phosphoribosyltransferases from four separate Japanese families with 2,8-dihydroxyadenine urolithiasis associated with partial enzyme deficiencies

2,8-Dihydroxyadenine urolithiasis associated with partial deficiencies of adenine phosphoribosyltransferase (APRT) has been found only among Japanese families. All Caucasian patients with the same lithiasis are completely deficient in this enzyme. Partially purified APRT from one of the Japanese families with the lithiasis associated with a partial deficiency of APRT had a reduced affinity for 5-phosphoribosyl-1-pyrophosphate (PRPP). In the present investigations, we have shown that this characteristic is common in mutant enzymes from all the four separate Japanese urolithiasis families associated with partial APRT deficiencies so far tested. The mutant enzymes also had several other characteristics in common including increased resistance to heat in the absence of PRPP and reduced sensitivity to the stabilizing effect of PRPP. These data suggest that these families have a common mutant allele (APRT*J) at the APRT gene locus.

Rapid method for the diagnosis of partial adenine phosphoribosyltransferase deficiencies causing 2,8-dihydroxyadenine urolithiasis

More than half of the Japanese patients with 2,8-dihydroxyadenine urolithiasis only partially lack adenine phosphoribosyltransferase (APRT), while all the Caucasian patients with the same disease completely lack the enzyme. APRT activities in healthy heterozygotes for the complete APRT deficiencies were at the same levels as the Japanese patients, and simple enzyme assay does not distinguish between these two conditions. We have previously shown, using viable T-cells, that the enzyme was non-functional in the cells from the Japanese patients although they contain considerable APRT activities in the cell extracts. In the present investigations, we devised a rapid method using erythrocytes for the diagnosis of partial APRT deficiencies accompanied by severe impairment in adenine metabolism causing 2,8-dihydroxyadenine lithiasis. Thus, erythrocytes from three different families with 2,8-dihydroxyadenine urolithiasis associated with partial APRT deficiencies incorporated only minimal amounts of radioactive adenine, while normal erythrocytes incorporated significant amounts. These data indicate that severe impairment in adenine metabolism is shown not only in viable T-cells but also in viable erythrocytes. The present procedures provide a rapid method suitable for routine clinical use for the diagnosis of partial APRT deficiencies causing 2,8-dihydroxyadenine lithiasis.

Human adenine phosphoribosyltransferase: characterization from subjects with a deficiency of enzyme activity

Adenine phosphoribosyltransferase (APRT) was characterized with respect to specific activity and immunoreactive protein (CRM) levels in hemolysate from 18 members of an APRT-deficient kindred. In addition, lymphoblastoid cell lines were established from six of these subjects and APRT from these cells was characterized in a similar fashion. Levels of specific activity and CRM in patients homozygous for the deficiency were less than 1% of normal. Heterozygous subjects had higher levels of activity and CRM in lymphoblasts than in erythrocytes and, in all cases, the APRT present was normal in terms of isoelectric point, subunit molecular weight, and heart stability. The higher levels of activity and CRM found in lymphoblasts may be due either to expression of a mutant gene product stabilized in a normal:mutant dimer or to autologous regulation.

2,8-dihydroxyadenine urolithiasis: review of the literature and report of a case in the United States

Urolithiasis resulting from inherited metabolic derangement is rare. Only 13 cases of 2,8-dihydroxyadenine stones resulting from a deficiency of the enzyme adenine phosphoribosyl transferase have been reported since 1974. Of these cases 9 have been in children with the homozygous trait. To date, 3 homozygous and 1 heterozygous adults with urolithiasis have been reported. This disease has not been associated with any other clinical or biochemical abnormalities. Treatment includes low purine diet and allopurinol. We herein report a case of complete adenine phosphoribosyl transferase deficiency associated with 2,8-dihydroxyadenine urolithiasis in the United States, bringing the total to 14 in the literature.

Complete deficiency of adenine phosphoribosyl transferase: report of a new family

We report a case of 2,8-dihydroxyadenine urinary lithiasis with complete deficiency of adenine phosphoribosyl transferase. Adenine phosphoribosyl transferase activities in the erythrocytes, lymphocytes and granulocytes of the patient's family also were determined. The propositus and her younger brother were homozygotes for adenine phosphoribosyl transferase deficiency and her parents were heterozygotes. This is the third family with this disease to be reported.

Infrared spectrometry and Raman microprobe in the analysis of urinary calculi

Infrared spectrophotometry and Raman spectroscopy, thanks to the laser molecular microsond (MOLE), are two analytical techniques particularly well suited to a precise analysis of the composition and structure of urinary calculi. They both showed noteworthy efficiency in their ability to recognize the various crystalline or amorphous mineral and organic species. The MOLE permits analysis of crystals 1 mu in size, demonstrating its usefulness in the study of calculi nuclei as well as in the study of urinary crystals. These analyses are a very important source of information about conditions of crystalline nucleation and growth as well as about ions and molecules which can take place in the formation and the evolution of the diverse crystalline phases. On the clinical level, these data can contribute to a better comprehension of the formation of every stone.

Renal failure due to 2,8-dihydroxyadenine urolithiasis

A four-year-old girl presented in renal failure due to dihydroxyadenine urolithiasis. Prior to this she had been fed a high purine macrobiotic diet, rich in pulses and grain. She was comatose, anuric, requiring peritoneal dialysis, and bilateral radiolucent renal calculi were revealed by ultrasonography and retrograde pyelography. 2,8-dihydroxyadenine stones were found at pyelolithotomy, renal biopsy revealed interstitial birefringent crystals, and a complete lack of adenine phosphoribosyl transferase (APRT) was found subsequently in erythrocyte lysates. APRT levels were initially falsely raised due to a blood transfusion on admission. The mother was shown to have heterozygote levels. The child was treated successfully with allopurinol, and a reduction in dietary purine but with only partial return of renal function.

Dependence of adenine production upon polyamine synthesis in cultured human lymphoblasts

The exact source of de novo adenine produced by mammalian cells remain poorly understood, and this prompted the present study. Using a human lymphoblastoid cell line (WI-L2) deficient in adenine phosphoribosyltransferase (EC 2.4.2.7), we have quantitated the rate of adenine synthesis and the relative importance of the phosphorolysis of 5'-methylthioadenosine versus adenosine or 2'-deoxyadenosine in adenine generation. Dividing adenine phosphoribosyltransferase-deficient WI-L2 cells produced adenine at a rate of 0.27 nmol/mg protein/h. This represented approximately 10% of the rate of hypoxanthine production by WI-L2 cells deficient in hypoxanthine phosphoribosyltransferase (EC 2.4.2.8) but was equivalent to the rate of 5'-methylthioadenosine synthesis by human lymphoblastoid CCRF-CEM deficient in 5'-methylthioadenosine, phosphorylase (5'-methylthioadenosine: orthophosphate methylthioribosyltransferase). Up to 97% of adenine, but not hypoxanthine, synthesis was inhibited dose-dependently by the S-adenosylmethionine decarboxylase-inhibitor methylglyoxal bis(guanylhydrazone) and also by spermidine and spermine, but was enhanced by putrescine. The addition of 2-fluoroadenine, a potent competitive inhibitor of methylthioadenosine phosphorylase (Ki = 0.43 microM) to adenine phosphoribosyl-transferase-deficient cells resulted in a progressive accumulation of 5'-methylthioadenosine in the culture medium, and up to an 85% decrease in adenine production at non-toxic concentrations. These results show that de novo adenine synthesis by dividing human cells is considerable, and that 85-97% derives from the cleavage of 5'-methylthioadenosine and hence from polyamine synthesis.

Characterization of the biochemical basis of a complete deficiency of the adenine phosphoribosyl transferase (APRT)

In order to study the biochemical basis of a complete deficiency of adenine phosphoribosyl transferase (APRT) the enzyme was purified to homogeneity, its properties were characterized, and antibodies raised. The enzyme is indirectly involved in adenine uptake. Apparently, by forming AMP the internal concentration of adenine is kept low allowing it diffusion. The same APRT is present in various tissues as was revealed by antibody inactivations employing anti-erythrocyte APRT as well as by direct enzyme assays in cells from the APRT deficient patient. In vitro cultured fibroblasts derived from this patient had less than 0.02% enzyme activity. No cross-reacting material was found in erythrocytes obtained from an APRT deficient child.

Structural features of the phosphoribosyltransferases and their relationship to the human deficiency disorders of purine and pyrimidine metabolism

Similarities in the physical and chemical properties of the phosphoribosyltransferase family of enzymes suggest that they may share common structural features as observed in other functionally related proteins. The unusually high incidence of structural gene mutations of these enzymes in man are associated with several metabolic diseases of purine and pyrimidine metabolism. It is proposed that these disorders are the consequence of structural mutations to an architectural domain common to all of the phosphoribosyltransferases.

Mouse teratocarcinoma mutant clones deficient in adenine phosphoribosyltransferase and developmentally pluripotent

Mouse teratocarcinoma stem cells deficient in activity of adenine phosphoribosyltransferase (APRT; EC 2.4.2.7) were obtained in order to have this marker in developmentally versatile cells. Mutagenized stem-cell cultures were selected for resistance to 8-azaadenine and four clonal cell lines were isolated. Three had severe deficiencies of APRT activity (7% or less of wild type) and one had a moderate reduction (73%). The enzyme in the latter clone was found to be an electrophoretic variant with slightly less anodal migration than the wild-type enzyme. Each clone remained stably APRT-deficient for at least 3 1/2 weeks, after subcutaneous inoculation, in the absence of the selective agent. The tumors formed from the inocula comprised a variety of differentiated tissues and thus showed persistence of stem-cell developmental pluripotency despite mutagenesis and selection. All mutants also retained the quasinormal karyotype (X/O sex chromosomal constitution, trisomy-19) of the parent line. These lines are appropriate for such uses as production (by blastocyst injection) of mouse models of the human genetic deficiency and for foreign-gene transfer, via teratocarcinoma cells, into mice.