Adenine phosphoribosyltransferase deficiency identified by urinary sediment analysis: cellular and molecular confirmation

Use of LightCycler mutation analysis to detect type II adenine phosphoribosyltransferase deficiency in two patients with 2,8-dihydroxyadeninuria

Recently, a number of methods have been devised for detection of mutations in the field of molecular genetics. The LightCycler system has been used for rapid PCR, while simultaneously quantifying and analyzing the amplification results. We tried to apply the LightCycler system to detect APRT*J allele mutations in two families including two children with 2,8-dihydroxyadenine urolithiasis. The first patient was a 3-year-old girl who presented with left flank pain. The second patient was a 2-year-old girl who presented with complaints of sudden dysuria. The spectrophotometric analysis of the stone fragments of both patients revealed an absorption spectrum for 2,8-DHA. We used the LightCycler system to detect APRT*J mutation. The first patient was homozygous for APRT*J/APRT*J and the second patient was compound heterozygous for APRT*J/APRT*Q0. The genetic diagnosis of APRT deficiency using this system may be useful not only as a diagnostic test for infants with known 2,8-DHA, but also as a screening of infants with a suspicion of urolithiasis. We believed that the LightCycler system still is an important means of identifying APRT*J mutation.

Uric acid changes in urine and plasma: an effective tool in screening for purine inborn errors of metabolism and other pathological conditions

Purine inborn errors of metabolism (IEM) are serious hereditary disorders, which should be suspected in any case of neonatal fitting, failure to thrive, recurrent infections, neurological deficit, renal disease, self-mutilation and other manifestations. Investigation usually starts with uric acid (UA) determination in urine and plasma. UA, the final product of purine metabolism in humans, may be altered not only in purine IEM, but also in other related pathologies and clinical conditions. However, data and information about abnormal UA levels are scattered in the literature, often being controversial and confusing. A comprehensive overview has been elaborated, according to abnormal UA levels in urine and plasma, which associates these alterations with purine IEM. Other possible diseases, clinical conditions, diet and drug intake, related to the metabolism of uric acid, are also presented. The article includes tables that classify the disorders according to different patterns of UA alterations, with pertinent enzymes, clinical symptoms, inheritance and comments. Additionally, summarized pathophysiological mechanisms of important disorders are described. The overview is intended to assist in the interpretation of the results of UA analyses. It demonstrates that variation of UA concentrations in urine and plasma may constitute an effective tool in screening for purine IEM and other related pathological conditions.

Clinical features and genotype of adenine phosphoribosyltransferase deficiency in iceland

The purpose of this study was to characterize the clinical, diagnostic, and prognostic features of adenine phosphoribosyltransferase (APRT) deficiency in Icelandic patients, as well as determine their genotype. Medical records of all known patients in Iceland were reviewed. Urinalysis and polymerase chain reaction-based DNA mutation analysis were performed in all patients, siblings, and living parents of index cases. Twenty-three individuals homozygous for type I APRT deficiency were identified in 16 families from 1983 to 1998. There were 12 males and 11 females, and the median age at diagnosis was 37 years (range, 0.5 to 62 years). Seventeen patients were index cases and 6 patients were diagnosed during screening of first-degree relatives. Eighteen patients had symptomatic disease, 15 of whom experienced nephrolithiasis; 4 patients had mild to moderate renal insufficiency, 1 patient had advanced renal failure, and 1 patient died of uremic complications. Six patients experienced recurrent urinary tract infections and 3 infants had a history of reddish-brown diaper stains. Five patients were asymptomatic; 3 of these patients were diagnosed during routine urinalysis and 2 patients were identified during family screening. Urinary 2,8-dihydroxyadenine crystals were detected in all cases, except for the patient who died of end-stage renal failure. All 23 patients were homozygous for the same mutation (D65V) in the APRT gene. Allopurinol therapy successfully prevented further stone formation and significantly improved renal function in most patients with renal insufficiency. Our results suggest that APRT deficiency may be more common than previously recognized and can lead to severe renal failure if left untreated.

Identification of two mutations in human xanthine dehydrogenase gene responsible for classical type I xanthinuria

Hereditary xanthinuria is classified into three categories. Classical xanthinuria type I lacks only xanthine dehydrogenase activity, while type II and molybdenum cofactor deficiency also lack one or two additional enzyme activities. In the present study, we examined four individuals with classical xanthinuria to discover the cause of the enzyme deficiency at the molecular level. One subject had a C to T base substitution at nucleotide 682 that should cause a CGA (Arg) to TGA (Ter) nonsense substitution at codon 228. The duodenal mucosa from the subject had no xanthine dehydrogenase protein while the mRNA level was not reduced. The two subjects who were siblings with type I xanthinuria were homozygous concerning this mutation, while another subject was found to contain the same mutation in a heterozygous state. The last subject who was also with type I xanthinuria had a deletion of C at nucleotide 2567 in cDNA that should generate a termination codon from nucleotide 2783. This subject was homozygous for the mutation and the level of mRNA in the duodenal mucosa from the subject was not reduced. Thus, in three subjects with type I xanthinuria, the primary genetic defects were confirmed to be in the xanthine dehydrogenase gene.

Similarity of in vivo somatic mutations at an autosomal adenine phosphoribosyltransferase locus between T- and B-cells in human peripheral blood

In vivo somatic mutations have been detected at several human loci by using clonal cultures of peripheral blood T-cells. It has not been fully understood whether or not the somatic mutations in T-cells are similar to those of other cell types. To address this issue, we cloned, from human peripheral blood, T- and B-cells with mutations at an autosomal adenine phosphoribosyltransferase (APRT) locus. For the efficient detection of somatic mutations at the APRT locus, a blood sample from a human individual heterozygous for germline APRT deficiency was used. T- and B-cells deficient in APRT enzyme activity were cloned from peripheral blood mononuclear cells using a selecting agent, 2,6-diaminopurine. The APRT-deficient mutant frequencies were on the order of 10(-4) in both T- and B-cells. The single-strand conformation polymorphism analysis of the APRT DNA of mutant B-cell clones suggested that the molecular mechanisms leading to the APRT deficiency in B-cells were similar to those in T-cells. Our observations suggest that both the frequency and the mode of in vivo somatic mutations occurring spontaneously at general autosomal loci in B-cells are similar to those in T-cells.