Correlation between adenylate metabolizing enzymes and adenine nucleotide levels of erythrocytes during blood storage in various media

Adenine phosphoribosyltransferase deficiency in the United Kingdom: two novel mutations and a cross-sectional survey

Background

Adenine phosphoribosyltransferase deficiency is an inborn error of metabolism that can cause kidney disease from crystalline nephropathy or kidney stones.

Methods

We present three cases from a single centre with varied presentations to illustrate how increasing awareness led to better patient identification. We then undertook a cross-sectional survey of all the patients identified from the Purine Research Laboratory in the UK since 1974.

Results

Our index case presented with recurrent nephrolithiasis and was diagnosed on stone analysis, the second case presented with acute kidney injury and the third case was identified from a biopsy undertaken for acute on chronic kidney injury. Genetic studies identified two novel mutations. Twenty patients were retrospectively identified. The mean age at diagnosis was 25 years (range 2–70); eight were <20 years, seven were 20–40 years and five were >40 years. Five of the 20 patients were deceased, 3 after end-stage renal disease (ESRD). Twelve have normal renal function, one had CKD stage 3, one had severe kidney disease and one was on dialysis.

Conclusions

Adenine phosphoribosyltransferase deficiency presents in a wide spectrum in all age groups. Patients can be completely asymptomatic and kidney disease may be incorrectly attributed to other conditions. Outcome is poor in late diagnosis and there is a high prevalence of ESRD. Patients with unexplained renal stone disease or deterioration in kidney function should be considered for screening. Identification and surveillance of patients in the UK can improve. There is now a rare disease registry with meetings organized that include patients, families and health care providers to improve awareness.

Recurrence of crystalline nephropathy after kidney transplantation in APRT deficiency and primary hyperoxaluria

Purpose of review

To provide transplant physicians with a summary of the pathogenesis and diagnosis of adenine phosphoribosyl transferase (APRT) deficiency and primary hyperoxaluria and, focussed on kidney transplantation, and to discuss interventions aimed at preventing and treating the recurrence of crystalline nephropathy in renal transplant recipients.

Source of information

Pubmed literature search.

Setting

Primary hyperoxaluria and APRT deficiency are rare inborn errors of human metabolism. The hallmark of these diseases is the overproduction and urinary excretion of compounds (2,8 dihydroxyadenine in APRT deficiency, oxalate in primary hyperoxaluria) that form urinary crystals. Although recurrent urolithiasis represents the main clinical feature of these diseases, kidney injury can occur as a result of crystal precipitation within the tubules and interstitium, a condition referred to as crystalline nephropathy. Some patients develop end-stage renal disease (ESRD) and may become candidates for kidney transplantation. Since kidney transplantation does not correct the underlying metabolic defect, transplant recipients have a high risk of recurrence of crystalline nephropathy, which can lead to graft loss. In some instances, the disease remains undiagnosed until after the occurrence of ESRD or even after kidney transplantation.

Key messages

Patients with APRT deficiency or primary hyperoxaluria may develop ESRD as a result of crystalline nephropathy. In the absence of diagnosis and adequate management, the disease is likely to recur after kidney transplantation, which often leads to rapid loss of renal allograft function. Primary hyperoxaluria, but not APRT deficiency, becomes a systemic disease at low GFR with oxalate deposition leading to malfunction in non-renal organs (systemic oxalosis). We suggest that these diagnoses should be considered in patients with low glomerular filtration rate (GFR) and a history of kidney stones. In APRT deficiency, stones may be confused with uric acid stones, unless specialized techniques are used (infrared spectroscopy or X-ray crystallography for urinary crystals or stone analysis; Fourier transform infrared microscopy for crystals in kidney biopsy). Where these are unavailable, and for confirmation, the diagnosis can be made by measurement of enzyme activity in red blood cell lysates or by genetic testing. In patients with primary hyperoxaluria, levels of urinary and plasma oxalate; and the presence of nearly pure calcium oxalate monohydrate in stones, which often also have an unusually pale colour and unorganized structure, increase diagnostic suspicion. Molecular genetic testing is the criterion measure. Lifelong allopurinol therapy, with high fluid intake if appropriate, may stabilize kidney function in APRT deficiency; if ESRD has occurred or is near, results with kidney transplantation after initiation of allopurinol are excellent. In primary hyperoxaluria recognized before ESRD, pyridoxine treatment and high fluid intake may lead to a substantial decrease in urinary calcium oxalate supersaturation and prevent renal failure. In non-responsive patients or those recognized later in their disease, liver transplantation cures the underlying defect and should be considered when the GFR falls below 30 ml/min/1.73 m²; in those which or near ESRD, liver transplantation and intensive dialysis before kidney transplantation may be considered to reduce the total body oxalate burden before kidney transplantation.

Limitations

The availability of diagnostic tests varies between countries and centres. Data on long term outcomes after kidney transplantation are limited, especially for APRT deficiency patients.

Implications

Increasing transplant physicians knowledge of APRT deficiency and primary hyperoxaluria should enable them to implement adequate diagnostic and therapeutic interventions, thereby achieving good outcomes after kidney transplantation.

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

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.

Phenotype and genotype characterization of adenine phosphoribosyltransferase deficiency

Adenine phosphoribosyltransferase (APRT) deficiency is a rare autosomal recessive disorder causing 2,8-dihydroxyadenine stones and renal failure secondary to intratubular crystalline precipitation. Little is known regarding the clinical presentation of APRT deficiency, especially in the white population. We retrospectively reviewed all 53 cases of APRT deficiency (from 43 families) identified at a single institution between 1978 and 2009. The median age at diagnosis was 36.3 years (range 0.5 to 78.0 years). In many patients, a several-year delay separated the onset of symptoms and diagnosis. Of the 40 patients from 33 families with full clinical data available, 14 (35%) had decreased renal function at diagnosis. Diagnosis occurred in six (15%) patients after reaching ESRD, with five diagnoses made at the time of disease recurrence in a renal allograft. Eight (20%) patients reached ESRD during a median follow-up of 74 months. Thirty-one families underwent APRT sequencing, which identified 54 (87%) mutant alleles on the 62 chromosomes analyzed. We identified 18 distinct mutations. A single T insertion in a splice donor site in intron 4 (IVS4 + 2insT), which produces a truncated protein, accounted for 40.3% of the mutations. We detected the IVS4 + 2insT mutation in two (0.98%) of 204 chromosomes of healthy newborns. This report, which is the largest published series of APRT deficiency to date, highlights the underdiagnosis and potential severity of this disease. Early diagnosis is crucial for initiation of effective treatment with allopurinol and for prevention of renal complications.

Erythrocyte adenine PRPP availability in two types of APRT deficiency using silicon oil method

Erythrocyte phosphoribosylpyrophosphate availability for adenine was measured by silicon oil method previously described. The homozygotes of Japanese type APRT deficiency (n = 6, from 4 families) showed 4.3 +/- 2.7% (mean +/- standard deviation) of adenine PRPP availability and the heterozygotes (n = 5) showed 86.0 +/- 6.0% of adenine PRPP availability. All homozygotes of Japanese type APRT deficiency from 4 unrelated families show the equally decreased adenine PRPP availability and it supports the presumption of the presence of the similar defect of APRT in all families. In a Japanese family of complete APRT deficiency, adenine PRPP availability of the homozygote was undetectable and that of the heterozygote was normal low (54.3% of normal mean activity). The adenine PRPP availability of the heterozygote of complete APRT deficiency was diagnostically different from that of the homozygotes of Japanese type APRT deficiency, despite, these two conditions showed almost the same erythrocyte APRT activity. These results prove that the silicon oil method previously written is the rapid and useful method for differential diagnosis between two types of APRT deficiency.

Distribution of patients with 2,8-dihydroxyadenine urolithiasis and adenine phosphoribosyltransferase deficiency in Japan

2,8-Dihydroxyadenine urolithiasis is caused by genetic deficiencies of adenine phosphoribosyl-transferase. This disease has occurred in a large number of Japanese patients and more than half of all families with this disease are only partially deficient in enzyme activities (Japanese type adenine phosphoribosyltransferase deficiency). To clarify the reasons for the preponderance of Japanese cases we sent questionnaires to 948 Japanese urological departments. The data thus obtained indicated that 76 families had 2,8-dihydroxyadenine lithiasis and of 51 families in which adenine phosphoribosyltransferase activities were assayed 76 per cent were only partially deficient in adenine phosphoribosyltransferase activities. The distribution of the 2,8-dihydroxyadenine families was roughly similar to that of the population in Japan and the rates of the Japanese type adenine phosphoribosyltransferase deficiency families were not significantly different among the various parts of Japan. These data indicate that the wide distribution of the unique mutant gene, APRT*J, that was created many years ago in a Japanese ancestor, explains at least in part the large number of 2,8-dihydroxyadenine lithiasis and adenine phosphoribosyltransferase deficiency families among the Japanese.

Human adenine phosphoribosyltransferase deficiency. Demonstration of a single mutant allele common to the Japanese

Complete adenine phosphoribosyltransferase (APRT) deficiency causes 2,8-dihydroxyadenine urolithiasis. In previous reports, analysis of the kinetic properties of APRT from APRT-deficient Japanese subjects revealed strikingly similar abnormalities suggesting a distinct "Japanese-type" mutation. In this paper, we report studies of 11 APRT-deficient lymphoblast cell lines. Nucleotide sequence analysis of APRT genomic DNA from WR2, a Japanese-type homozygote, identified a T to C substitution in exon 5, giving rise to the substitution of threonine for methionine at position 136. RNase mapping analysis confirmed this mutation in WR2 and revealed that six other Japanese-type homozygotes carry the same mutation on at least one allele. The remaining Japanese subject, who does not express the Japanese-type phenotype, did not demonstrate this mutation. Southern blot analysis showed that all seven Japanese-type subjects were confined to one TaqI restriction fragment length polymorphism (RFLP) haplotype. These studies provide direct evidence for the nature of the mutation in the Japanese-type APRT deficiency.

Human adenine phosphoribosyltransferase. Identification of allelic mutations at the nucleotide level as a cause of complete deficiency of the enzyme

This study reports the first demonstration of specific mutations leading to human adenine phosphoribosyltransferase (APRT) deficiency. The molecular basis of the deficiency was investigated by determining the sequence of both alleles of a patient with a complete deficiency in APRT activity. A trinucleotide deletion, corresponding to phenylalanine on the deduced amino acid sequence, was confirmed on one allele. A single nucleotide insertion, immediately adjacent to the splice site at the 5' end of the fourth intervening sequence, was confirmed on the other allele. This insertion lead to aberrant splicing, as was demonstrated by the absence of exon 4 in the complementary DNA sequence and by altered RNase mapping analysis of the abnormal messenger RNA.

A coupled optical assay for adenine phosphoribosyltransferase and its extension for the spectrophotometric and radioenzymatic determination of 5-phosphoribosyl-1-pyrophosphate in mixtures and in tissue extracts

A reliable assay was developed to characterize crude cell homogenates with regard to their adenine phosphoribosyltransferase activities. The 5-phosphoribosyl-1-pyrophosphate (PRPP)-dependent formation of AMP from adenine is followed spectrophotometrically at 265 nm by coupling it with the following two-stage enzymatic conversion: AMP + H2O----adenosine + Pi (5'-nucleotidase); adenosine + H2O----inosine + NH3 (adenosine deaminase). The same principle was applied to develop a spectrophotometric and a radioenzymatic assay for PRPP. The basis of the spectrophotometric assay is the absorbance change at 265 nm associated with the enzymatic conversion of PRPP into inosine, catalyzed by the sequential action of partially purified adenine phosphoribosyltransferase, commercial 5'-nucleotidase, and commercial adenosine deaminase, in the presence of excess adenine. In the radiochemical assay PRPP is quantitatively converted into [14C]inosine via the same combined reaction. Tissue extracts are incubated with excess [14C]adenine. The radioactivity of inosine, separated by a thin-layer chromatographic system, is a measure of PRPP present in tissue extracts. The radioenzymatic assay is at least as sensitive as other methods based on the use of adenine phosphoribosyltransferase. However, it overcomes the reversibility of the reaction and the need to use transferase preparations free of any phosphatase and adenosine deaminase activities.

Genetic and clinical studies on 19 families with adenine phosphoribosyltransferase deficiencies

Adenine phosphoribosyltransferase (APRT) deficiency leading to 2,8-dihydroxyadenine (DHA) urolithiasis has been considered a rare cause of urolithiasis and renal insufficiency. We have examined samples from 19 Japanese families with DHA lithiasis. In 79% of the families, patients only partially lacked hemolysate APRT activities, clearly contrasting with the complete deficiency in all the patients from non-Japanese families so far reported. All patients with DHA lithiasis were homozygotes for defective APRT genes, whether the deficiency was complete or partial. In family studies we found two symptomatic and four asymptomatic homozygous family members. The segregation figures are compatible with the hypothesis of a simple autosomal recessive mode of inheritance. By analyzing the data stored by a large clinical laboratory in Japan, we estimated that 0.00368% of the general population has DHA lithiasis. These data indicate that more than 1% of the general population possess mutant alleles of the APRT gene as heterozygotes. Our present studies indicate that most of the patients with this disease are undiagnosed in Japan, and probably in other countries also.

Establishment and characterization of B cell lines from individuals with various types of adenine phosphoribosyltransferase deficiencies

Patients with 2,8-dihydroxyadenine urolithiasis are either completely or partially deficient in adenine phosphoribosyltransferase activities. Patients with partial enzyme deficiencies, all of whom have been found among Japanese, are homozygotes having a unique mutant adenine phosphoribosyltransferase gene (APRT*J) in double dose (Japanese type deficiency). We have established B-cell lines from heterozygotes and homozygotes of complete and Japanese type adenine phosphoribosyltransferase deficiencies as well as normal individuals. Characterization of the cell lines indicated that all homozygous cells were deficient in adenine phosphoribosyltransferase function while all heterozygous and normal cells had functional adenine phosphoribosyltransferase.

Altered kinetic properties of a mutant adenine phosphoribosyltransferase

Three siblings in a Japanese family experienced recurrent 2,8-dihydroxyadenine urolithiasis despite the presence of adenine phosphoribosyltransferase (APRT) activities in the hemolysates (19.9% to 28.2% of normal value). However, studies on viable T cells from these patients indicated that APRT was not functional in viable cells. Further analysis of the partially purified enzymes from hemolysates disclosed that patient's APRT had a reduced affinity to 5-phosphoribosyl-1-pyrophosphate (PRPP). Seven healthy members of this family whose APRT functioned normally in viable T cells had the erythrocyte enzyme levels between the patients and normal individuals (38.2% to 65.6%), suggesting that they are carriers of the defective gene. These results indicate that the defective gene code a unique mutant APRT with a reduced affinity to PRPP, and the patients are homozygotes. The mutant enzyme was also shown to be more heat-stable than normal enzyme. However, since mutant enzyme, unlike normal enzyme, was insensitive to the stabilization effect of PRPP, the latter became more heat-stable than the former when the heat treatment was performed in the presence of PRPP. This type of defect with alterations in the kinetic and physical properties of APRT as described here is likely to be a common type of APRT deficiency in Japan.

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.

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.

Purine reutilization and synthesis de novo in long-term human lymphocyte cell lines deficient in adenine phosphoribosyltransferase activity

Clonal lines, with either partial or total deficiency of adenine phosphoribosyltransferase (APRT) were derived from the WI-L2 long-term human lymphocyte line by selection for resistance to the adenine analogs 8-azaadenine or 2,6-diaminopurine. Resistance to 8-azaadenine also conferred resistance to 2,6 diaminopurine and vice versa. Cells with 30--40% of wild-type APRT activity were selected by resistance to 0.01 mM 2,6-diaminopurine or 1.40 mM 8-azaadenine. The APRT in the 8-azaadinine-resistant cells exhibited a four- to sevenfold increase in the apparent Km for adenine. Activities of three other purine reutilization and interconversion enzymes in the resistant cells, including hypoxanthine phosphoribosyltransferase (HPRT), adenosine kinase, and adenosine deaminase, were within the range of wild-type activities. The doubling times of the APRT-deficient cells in purine-free medium was not different from wild-type cells. The APRT in the 8-azaadenine-resistant cells did not have an altered mobility in glycerol gradients as compared to wild-type cells. The rate of purine synthesis de novo and intracellular levels of 5-phosphoribosyl-1-pyrophosphate were unchanged in the APRT-deficient cells as compared to WI-L2. The ability of the cells to reutilize exogenous adenine, however, was severely impaired.