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

Decreased kidney function and crystal deposition in the tubules after kidney transplant

Adenine phosphoribosyltransferase (APRT) deficiency is an autosomal recessive purine enzyme defect that results in the inability to utilize adenine, which consequently is oxidized by xanthine dehydrogenase to 2,8-dihydroxyadenine (2,8-DHA), an extremely insoluble substance eventually leading to crystalluria, nephrolithiasis, and kidney injury. We describe a case of APRT deficiency not diagnosed until the evaluation of a poorly functioning kidney transplant in a 67-year-old white woman. After the transplant, there was delayed transplant function, urine specimens showed crystals with unusual appearance, and the transplant biopsy specimen showed intratubular obstruction by crystals identified as 2,8-DHA using infrared spectroscopy. APRT enzymatic activity was undetectable in red blood cell lysates, and analysis of the APRT gene showed 1 heterozygous sequence variant, a duplication of T at position 1832. The patient was treated with allopurinol, 300 mg/d, and transplant function progressively normalized. Because patients with undiagnosed APRT deficiency who undergo kidney transplant may risk losing the transplant because of an otherwise treatable disease, increased physician awareness may hasten the diagnosis and limit the morbidity associated with this disease.

Crystalline nephropathy due to 2,8-dihydroxyadeninuria: an under-recognized cause of irreversible renal failure

BACKGROUND

2,8-dihydroxyadeninuria (DHA) disease (also called 2,8 dihydroxyadeninuria) is a rare autosomal recessive disorder caused by complete adenine phosphoribosyltransferase deficiency and typically manifests as recurrent nephrolithiasis. Only rare cases of DHA nephrolithiasis have been reported from the USA. Herein, we report three American patients who developed DHA crystalline nephropathy leading to end-stage renal disease (ESRD) with recurrence in the allograft.

METHODS

Three cases of DHA crystalline nephropathy were identified from the Renal Pathology Laboratory of Mayo Clinic. Detailed clinical and pathologic descriptions are provided.

RESULTS

All three patients were Caucasian adults with no history of obstructive nephropathy. Two patients had no history of nephrolithiasis and one had a single episode of stones 36 years prior to presentation. All patients presented with severe renal failure with a mean serum creatinine of 7.5 mg/dl. Renal biopsies revealed numerous tubular and interstitial brown DHA crystals, tubular degenerative changes and moderate to marked tubulointerstitial scarring. Two patients were initially misdiagnosed, one as primary hyperoxaluria and the other as chronic interstitial nephritis. All three patients progressed to ESRD, within 1 month following renal biopsy in two and after 9 months in one. All three patients underwent renal transplantation with early disease recurrence in three allografts in two patients.

CONCLUSIONS

DHA disease is an under-recognized condition that can lead to irreversible renal failure and frequently recurs in the transplant. It should be included in the differential diagnosis of crystalline nephropathy, even in the absence of history of nephrolithiasis.

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.

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.

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.

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.

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.

2,8-Dihydroxyadenine lithiasis

2,8-Dihydroxyadenine (2,8-DHA) lithiasis is a form of kidney stone previously mistaken for uric acid because of identical reactivity in non-specific tests used routinely in stone analysis. Unlike uric acid, the stones crush easily and do not react with uricase. The biochemical basis for the defect is a deficiency of the enzyme adenine phosphoribosyltransferase (APRT). A complete deficiency has been reported in 29 patients from 11 countries. The number of stone formers reported in Japan (10 homozygotes, 16 heterozygotes) Austria (3), and Switzerland (2) suggests more efficient diagnosis in those countries. The defective enzyme in heterozygotes in Japan is a kinetic mutant demonstrable in intact not lysed cells. 20% of APRT-deficient subjects have been asymptomatic. An equal number have presented in acute renal failure, three of whom are now on dialysis. Formation of the nephrotoxic 2,8-DHA can be prevented by allopurinol. This underlines the importance of early diagnosis, since such severe renal damage should be avoidable.

Etiopathogenesis of uncommon canine uroliths. Xanthine, carbonate, drugs, and drug metabolites

Metabolic disorders, medication, and diagnostic agents may be associated with urolithiasis in dogs. Examples of uroliths that have been uncommonly encountered in dogs include xanthine, dolomite, tetracycline, and sulfonamides. Detection of these and other apparently uncommon uroliths requires a high index of suspicion and proper methods of analysis.

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.