Guanine Phosphoribosyltransferase Deficiency Research Articles

Hyperuricemia and gout due to deficiency of hypoxanthine–guanine phosphoribosyltransferase in female carriers: New insight to differential diagnosis

BackgroundX-linked hypoxanthine–guanine phosphoribosyltransferase (HPRT) deficiency in an inherited disorder of purine metabolism is usually associated with the clinical manifestations of hyperuricemia. A variable spectrum of neurological involvement occurs predominantly in males. Females are usually asymptomatic. Carrier status cannot be confirmed by biochemical and enzymatic methods reliably. MethodsWe studied clinical, biochemical and molecular genetic characteristics of Czech families with hyperuricemia and HPRT deficiency. We analyzed age at diagnosis, clinical symptoms, uricemia, urinary hypoxanthine and xanthine, HPRT activity in erythrocytes, mutation in the HPRT1 gene, X-inactivation, and major urate transporters. ResultsA mutation in the HPRT1 gene in family A was confirmed in one boy and four females. Three females with hyperuricemia had normal excretion of purine. One female was normouricemic. An 8-month-old boy with neurological symptoms showed hyperuricemia, increased excretion of urinary hypoxanthine and xanthine and a very low HPRT activity in erythrocytes. We have found three other unrelated female carriers with hyperuricemia and normal excretion of hypoxanthine and xanthine among other families with HPRT deficiency. ConclusionsHPRT deficiency needs to be considered in females with hyperuricemia with normal excretion of purine metabolites. Familiar hyperuricemia and/or nonfamiliar gout should always be further investigated, especially in children.

Hydrophilic-interaction liquid chromatography-tandem mass spectrometric determination of erythrocyte 5-phosphoribosyl 1-pyrophosphate in patients with hypoxanthine-guanine phosphoribosyltransferase deficiency.

Mutations in the gene encoding hypoxanthine-guanine phosphoribosyltransferase (HPRT) cause Lesch-Nyhan disease (LND) and its variants (LNV). Due to the technical problems for measuring the HPRT activity in vitro, discordances between the residual HPRT activity and the clinical severity were found. 5-Phosphoribosyl 1-pyrophosphate (PRPP) is a substrate for HPRT. Since increased PRPP concentrations were observed in erythrocytes from patients with LND and LNV, we have turned our attention to erythrocyte PRPP as a biomarker for the phenotype classification. In the present work, a method for determination of PRPP concentration in erythrocyte was developed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) with multiple reaction monitoring (MRM). Packed erythrocyte samples were deproteinized by heating and the supernatants were injected into the LC-MS/MS system. All measurement results showed good precision with RSD <6%. PRPP concentrations of nine normal male subjects, four male patents with LND and six male patients with LNV were compared. The PRPP concentrations in erythrocyte from patients with LND were markedly increased compared with those from normal subjects, and those from patients with LNV were also increased but the degree was smaller than those with LND. The increase pattern of PRPP concentration in erythrocyte from patients with HPRT deficiency was consistent with the respective phenotypes and was correlated with the disease severity. PRPP concentration was suggested to give us supportive information for the diagnosis and the phenotype classification of LND and LNV.

The spectrum of hypoxanthine – guanine phosphoribosyltransferase deficiency in Poland

The spectrum of hypoxanthine – guanine phosphoribosyltransferase deficiency in Poland

Novel HGPRT 293 A&gt;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.

Partial hypoxanthine–guanine phosphoribosyl transferase deficiency without elevated urinary hypoxanthine excretion

Partial hypoxanthine–guanine phosphoribosyl transferase (HGPRT) deficiency, also known as the Kelley–Seegmiller syndrome, can give rise to a wide range of neurological symptoms, and renal insufficiency. Biochemically, it is characterized by high uric acid concentrations in blood, high uric acid and hypoxanthine excretion in urine, and decreased activity of hypoxanthine–guanine phosphoribosyl transferase activity (HGPRT). However, normal uric acid concentrations in blood and uric acid excretions in urine have been reported. Here, a boy is presented with normal development and suffering from recurrent attacks of acute renal failure with slightly to clearly increased urinary uric acid excretion. Between these attacks, episodes of elevated urinary excretion of uric acid were observed with normal blood concentrations of uric acid and normal urinary excretion of hypoxanthine. HGPRT activity in erythrocytes, leukocytes, and fibroblasts was found to be strongly decreased. This case shows that not only normal blood uric acid but also normal urinary hypoxanthine concentrations do not exclude the diagnosis of partial HGPRT deficiency.

A novel missense mutation, c.584A > C (Y195S), in two unrelated Argentine patients with hypoxanthine–guanine phosphoribosyl-transferase deficiency, neurological variant

The hypoxanthine–guanine phosphoribosyl-transferase (HPRT) deficiency is an inborn error of purine metabolism, responsible for classic Lesch–Nyhan disease and its neurological and hyperuricemic variants. We report a novel mutation in the HPRT gene, c.584A > C (Y195S), in two unrelated Argentine patients affected with the neurological variant with no HPRT activity in lysed erythrocytes. Using PCR plus DNA sequencing and/or restriction enzyme digestion we were able to confirm the diagnosis and identify new cases and potential carriers.

Failure to adequately use positive control data leads to poor quality mouse lymphoma data assessments.

The mouse lymphoma L5178Y/TK1/–-3.7.2C mutagenesis assay (MLA) is widely used to identify chemicals that are capable of inducing mutational damage (Mitchell et al., 1997). Mutants detected in the assay form a bimodal distribution based on colony size. More than two decades of research demonstrate that both small and large colony trifluorothymidine-resistant (TFTr) colonies are ‘true mutants’ and that the assay detects the broad spectrum of genetic damage known to be involved in the etiology of cancer (Moore-Brown et al., 1981; Moore et al., 1985b; Applegate et al., 1990; Hozier et al., 1992). Because the assay detects mutagens that act through a variety of mechanisms, the MLA is specifically recommended by regulatory agencies for inclusion in hazard identification screening for environmental chemicals and pharmaceuticals (Dearfield et al., 1991; ICH3, 1996). Because of the ability of the MLA to detect both point mutations and chromosomal mutations, it would be expected that some chemicals would be positive in the MLA but not in the Salmonella assay, which only detects chemicals capable of inducing point mutations. In addition, it would be expected that the MLA would yield mutant frequencies (including the spontaneous background mutant frequency) far higher than those characteristic of other gene mutation assays, such as hypoxanthine guanine phosphoribosyl transferase deficiency and ouabain resistance, which by their nature are unable to detect the same broad spectrum of mutational events (Moore et al., 1989). In fact, mutant frequencies .1000310–6 have been induced by a number of chemicals (Clive et al., 1979; Moore et al., 1989; Backer et al., 1990; Moore and Doerr, 1990). A properly conducted MLA includes the demonstration that both small and large colony mutants have been optimally quantitated. This is accomplished by the appropriate use of the positive control. Chemicals that have been successfully used as positive controls (in the absence of exogenous activation) include methyl methanesulfonate (MMS), ethyl methanesulfonate (EMS) and hycanthone. Mutant frequencies for these chemicals (and colony sizing information) were published in

Purine metabolism in female heterozygotes for hypoxanthine-guanine phosphoribosyltransferase deficiency.

Female carriers of the X-linked recessive disorder hypoxanthine-guanine phosphoribosyltransferase (HPRT) deficiency show somatic cell mosaicism, and this may cause an increased synthesis of purines. We have examined whether urinary oxypurines could be useful for carrier diagnosis. Carrier testing was performed in 35 women belonging to 16 unrelated Spanish families with at least one subject affected by the Lesch-Nyhan syndrome (11 families, 14 patients) or the Kelley-Seegmiller syndrome (five families, six patients) by means of HPRT and adenine phosphoribosyltransferase activities in hair follicles and/or molecular studies. Plasma and 24-h urinary concentrations of hypoxanthine, xanthine and uric acid were measured while subjects were on a purine-restricted diet. Mean plasma urate concentrations and 24-h urinary hypoxanthine, xanthine and uric acid excretion rates were significantly higher in 22 heterozygotes than in 13 non-carriers (P < 0.02). Daily urinary oxypurine excretion rates were also significantly higher in heterozygotes than in 12 normal women (P = 0.0011). Cumulative 5-day radioactivity excretion after [8-14C]-adenine infusion was markedly increased in 10 carrier women compared with five normal women (P = 0.0369). The sensitivity of 24-h urinary hypoxanthine and xanthine excretion rates was 86% and 77%, respectively, and the specificity 100% for both tests. Female heterozygotes for HPRT deficiency show an enhanced purine nucleotide degradation and purine overproduction. An elevated hypoxanthine and/or xanthine excretion rate differentiated most heterozygotes for HPRT deficiency from non-carrier women and thus could be useful for carrier diagnosis.

Analysis of abnormalities in purine metabolism leading to gout and to neurological dysfunctions in man.

A modelling approach is used to analyse diseases associated with purine metabolism in man. The specific focus is on deficiencies in two enzymes, hypoxanthine:guanine phosphoribosyltransferase and adenylosuccinate lyase. These deficiencies can lead to a number of symptoms, including neurological dysfunctions and mental retardation. Although the biochemical mechanisms of dysfunctions associated with adenylosuccinate lyase deficiency are not completely understood, there is at least general agreement in the literature about possible causes. Simulations with our model confirm that accumulation of the two substrates of the enzyme can lead to significant biochemical imbalance. In hypoxanthine:guanine phosphoribosyltransferase deficiency the biochemical mechanisms associated with neurological dysfunctions are less clear. Model analyses support some old hypotheses but also suggest new indicators for possible causes of neurological dysfunctions associated with this deficiency. Hypoxanthine:guanine phosphoribosyltransferase deficiency is known to cause hyperuricaemia and gout. We compare the relative importance of this deficiency with other known causes of gout in humans. The analysis suggests that defects in the excretion of uric acid are more consequential than defects in uric acid synthesis such as hypoxanthine:guanine phosphoribosyltransferase deficiency.

HGPRT and APRT activities in hemolysates during the first year of life.

Early postnatal diagnosis of hypoxanthine guanine phosphoribosyl transferase (HGPRT) deficiency is frequently performed nowadays during the first year of life. The clinical expression of HGPRT deficiency is usually manifested by a variable psychomotor retardation between 6 and 12 months of age and may result in a variety of clinical syndromes, with markedly different neurological manifestations or even no neurological symptoms. At this age, or even earlier, parents or pediatricians may seek medical attention because they notice some developmental retardation in their child, sandy or coloured urine in the diapers, and/or because hyperuricemia and/or hyperuricosuria was discovered incidentally. Also babies belonging to a family with some male affected by this enzyme deficiency may seek early diagnosis (1).

Lesch—Nyhan syndrome: Carrier and prenatal diagnosis

We report the results of carrier and prenatal diagnosis for hypoxanthine guanine phosphoribosyltransferase (HPRT) deficiency, Lesch-Nyhan syndrome, by carrier testing of 83 women and prenatal analysis of 26 pregnancies. Our diagnostic methodologies include mutation detection and linkage analysis for probands and their families and biochemical measurement of HPRT enzyme activity for at-risk pregnancies. Identification of the mutation in the index case of each family permits precise carrier diagnosis using polymerase chain reaction (PCR) amplification of HPRT gene sequences and automated DNA sequencing. We demonstrate 100 per cent sensitivity for the detection of mutations in the HPRT gene of affected males and highly efficient carrier testing of at-risk females. Two other molecular methods proven to have high utility include PCR-based dosage analysis and linkage analysis by PCR amplification of a short tandem repeat (STR) in intron 3 of the HPRT gene. As a result, 45 at-risk women, 56 per cent of those tested, were identified not to be carriers of their family's HPRT gene mutation. Seven of these women were the mothers of affected males and prenatal testing for future pregnancies was recommended because of the possibility of gonadal mosaicism. Thirty-eight of these women were more distant relatives of affected males, thereby eliminating the need for future prenatal procedures. These studies illustrate the utility and precision of molecular methodologies for carrier and prenatal diagnosis of Lesch-Nyhan syndrome. These studies also illustrate that molecular diagnostic studies of affected males and carrier testing prior to pregnancy can clarify genetic risk predictions and eliminate unnecessary prenatal procedures.

The pathogenesis of the Lesch‐Nyhan syndrome: ATP use is positively related to hypoxanthine supply to hypoxanthine guanine phosphoribosyltransferase

In order to explain features of severe hypoxanthine guanine phosphoribosyltransferase (HPRT) deficiency, the Lesch-Nyhan syndrome, a continuous supply of substrate, hypoxanthine, for the enzyme must be generated. This supply must be increased in association with increased ATP turnover. We have shown that ATP turnover continuously supplies hypoxanthine for recycling by the enzyme HPRT and that this supply increases curvilinearly with increasing ATP turnover. The effects of increasing exercise on ATP turnover were examined using a Latin square experimental design. The outputs of hypoxanthine, xanthine, urate and creatinine were measured. The data were then examined statistically.

Hypoxanthine guanine phosphoribosyltransferase deficiency: nucleotide substitution causing Lesch-Nyhan syndrome identified for the first time among Japanese

A previously undescribed nucleotide substitution at codon 51 (CGA to TGA) has been identified using the polymerase chain reaction technique in hypoxanthine guanine phosphoribosyltransferase (HPRT) cDNA; this is the first molecular evidence for a point mutation in a Japanese patient with Lesch-Nyhan syndrome. The present mutation is the 19th nucleotide substitution identified as a germ-line mutation at this locus and the second mutation generating a stop codon. The position of the nucleotide substitution is exactly the same as a previously described mutation HPRTToronto, indicating for the first time that nucleotide substitutions at the same position in the sequence of HPRT can generate different mutant alleles, one causing a partial deficiency and the other a complete deficiency. Although the type of nucleotide substitution is different between the two cases, a single base position has twice become the target of a mutation. However, the calculation of the probability of finding substitution mutations at the same base position in the coding region of hprt indicates that there is no evidence for the presence of a hot spot for substitution mutations in the human hprt germ line.

Regulation of nicotinamide–adenine dinucleotide synthesis in erythrocytes of patients with hypoxanthine–guanine phosphoribosyltransferase deficiency and a patient with phosphoribosylpyrophosphate synthetase superactivity

1. The synthesis of nicotinamide-adenine dinucleotide from nicotinamide and nicotinic acid was compared over different time scales at both physiological (0.7 mumol/l) and high (0.2-3 mmol/l) substrate concentrations in erythrocytes from three patients with hypoxanthine-guanine phosphoribosyltransferase (hypoxanthine phosphoribosyltransferase, EC 2.4.2.8) deficiency (including one Lesch-Nyhan patient) and from one patient with phosphoribosylpyrophosphate synthetase superactivity. The above disorders are associated with grossly altered erythrocyte nicotinamide-adenine dinucleotide levels. 2. At the physiological substrate concentration and incubation times up to 2 h, nicotinamide proved the most efficient nicotinamide-adenine dinucleotide precursor for erythrocytes from both patients and control subjects. The conversion of nicotinamide to its mononucleotide, but not further metabolism, was impaired in phosphoribosylpyrophosphate synthetase-mutant cells. The Lesch-Nyhan and phosphoribosylpyrophosphate synthetase-mutant cells were unusual in that both showed no further stimulation of nucleotide synthesis at 18 mmol/l Pi compared with 1 mmol/l. 3. At the high substrate concentrations, using 18 mmol/l Pi, nicotinamide was a poor precursor in all instances. Using nicotinic acid, nucleotide formation was 30-fold that from nicotinamide, reaching its maximum at 0.2 mmol/l. Conversion of nicotinic acid to nicotinamide-adenine dinucleotide in the phosphoribosylpyrophosphate synthetase-mutant cells was again grossly impaired. 4. There was no evidence for increased nicotinamide-adenine dinucleotide breakdown in the phosphoribosylpyrophosphate synthetase-mutant cells under any of the above conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Classic disease descriptions in the modern curriculum

The rising number of laboratory tests and procedures ordered by physicians have contributed to increasing health care costs [l]. An increasing dependence on laboratory tests appears to have replaced confidence in the interpretation of data obtained from history and physical examination. Clinical skills have been deemphasized in undergraduate medical education, and the acquisition of these skills may be less exciting to students and teachers than an understanding of newer diagnostic technologies [2]. This trend is reflected in the development of the modern medical textbook. The standard medical text expands with each edition as it attempts to keep pace with new and complex diagnostic and treatment modalities. At the same time, clinical descriptions of disease have been condensed and simplified. The premise of this essay is that the precise and elegant pictures of disease presented in the writings of the great clinicians of the past should be reintroduced into current curriculum to reestablish the primary role of listening to and examining patients. These clinicians, dependent on bedside skills, preserved their lifetimes of clinical wisdom in their writings. More importantly, these writings may inspire students to appreciate signs and symptoms of disease better than modern-day books or teachers. Clinical descriptions of disease from previous eras can supplement modern clinical texts. For example, gout is discussed in 10 pages of text in Cecil’s 18th edition published in 1988. Discussion of the disease includes genetics, prevalence in relation to serum uric acid, mechanisms of hyperuricemia, purine biosynthesis, crystal-phagocyte interaction, pathology of tophi, clinical manifestions, gouty nephropathy, gout with specific enzyme deficiencies including glycogen storage disease type I, hypoxanthine guanine phosphoribosyltransferase deficiency, and phosphoribosylpyrophosphate synthetase variants, diagnosis, and treatment. One paragraph is devoted to clinical symptoms and reads as follows:

Chemiluminescent assays in the study of purine metabolism.

The discovery that in cells from patients with hypoxanthine guanine phosphoribosyltransferase (HGPRT) deficiency purine overproduction is associated with an elevated intracellular concentration of phosphoribosylpyro-phosphate (PRPP) (1) has led to a reevaluation of the importance of this compound in the regulation of purine biosynthesis de novo. The work which flowed from this discovery led to the identification of an inherited super-activity of PRPP synthetase in over a dozen families in which affected individuals showed gout and/or uric acid overproduction (2). However to date HGPRT deficiency and increased activity of PRPP synthetase are the only two well documented enzyme defects of purine synthesis and reutilization identified among hyperuricemic patients. These genetic aberrations account for less 10% of all hyperuricemic patients who overproduce uric acid.

Genetic basis of hypoxanthine guanine phosphoribosyltransferase deficiency in a patient with the Lesch-Nyhan syndrome (HPRT Flint)

The molecular basis for complete hypoxanthine guanine phosphoribosyltransferase (HPRT) deficiency has been determined in a patient with Lesch-Nyhan syndrome. A B-lymphoblastoid cell line derived from this patient expresses normal amounts of HPRT mRNA yet no detectable immunoreactive protein as determined by radioimmunoassay. These findings suggest either a decreased rate of translation or accelerated degradation due to enhanced proteolytic susceptibility. cDNAs synthesized from this patient's RNA have a single nucleotide (nt) substitution, a C → A transversion at nt 222. RNase A cleavage analysis confirms the presence of a mutation at this position within mRNA isolated from lymphoblasts from patient A.C. This transversion predicts a phenylalanine to leucine replacement at amino acid position 73 in the translated protein. We have designated this mutant HPRT Flint. The mutation in HPRT Flint disrupts a strongly conserved region among PRTases from Escherichia coli, rodents and man, suggesting an important role for this region for the normal function of HPRT. Since it is unlikely that this amino acid substitution alters the translational rate, we hypothesize that disruption of the secondary structure within this region renders HPRT Flint more susceptible to proteolysis.

Lesch-Nyhan syndrome: growth delay, testicular atrophy and a partial failure of the 11 beta-hydroxylation of steroids.

There is a failure of growth in hypoxanthine guanine phosphoribosyltransferase deficiency; slow weight gain is marked after the second year of age but is apparent in the birth weights of all eight of our patients for whom we have data. However, head growth and bone development are less affected than weight. A partial defect in the adrenocortical 11 beta-hydroxylation of steroids was demonstrated after ACTH stimulation in all four patients studied. This hydroxylation takes place in mitochondria the function of which is modulated by purine nucleotide concentrations; this may be the link with the enzyme defect. Testicular atrophy at autopsy was found in two pubertal age boys and seven patients aged 12-17 years had no signs of puberty. All five boys aged 3-11 years showed less than the normal mean response of plasma testosterone concentration to human chorionic gonadotrophin despite the normal histological appearance of the testes of one 6-year-old-boy. Follicle stimulating hormone responses to gonadotrophin releasing hormone are probably less than in normal in at least three of the seven prepubertal boys. The absence of the normally high activities of hypoxanthine guanine phosphoribosyltransferase in testes appears to inhibit their ability to respond to gonadotrophin.

Clinical correlations in partial hypoxanthine guanine phosphoribosyltransferase deficiency

Erythrocyte assays for hypoxanthine guanine phosphoribosyltransferase (HGPRT) activity performed on two male half-siblings with hyperuricemia, produced results consistent with classic Lesch-Nyhan syndrome. Due to the absence of neurologic abnormalities, cognitive deficits, or self-mutilation, HGPRT activity was measured by intact fibroblast assay which revealed partial enzyme deficiency. The presence of an unstable mutant enzyme may have led to the discrepancy between the erythrocyte and fibroblast studies. This discrepancy emphasizes the difficulty in assaying this enzyme solely utilizing red blood cell studies to determine a patient's course. In order to provide an accurate prognosis and relevant genetic counseling, measurement of this enzyme utilizing intact fibroblasts is critical after establishing a diagnosis of HGPRT deficiency in a hyperuricemic male lacking typical clinical manifestations of Lesch-Nyhan syndrome, but having enzyme activity of erythrocytes consistent with the diagnosis.

ERYTHROCYTE GTP DEPLETION IN PNP DEFICIENCY PRESENTING WITH HAEMOLYTIC ANAEMIA AND HYPODRICAEMIA: 193

A 4-yr old Arab girl,referred for investigation of hypouricaemia and hypouricosuria discovered during studies for Coombes positive haemolytic anaemia,was found to excrete inosine, guanosine,deoxyinosine and deoxyguanosine in place of uric acid. The patient and a 10-month old brother were homozygous for purine nucleoside phosphorylase (PNP) deficiency. Three of the other four surviving siblings were heterozygotes,as were the parents who were first cousins. Another sibling had died of chicken-pox. The baby showed head-lag, the girl spastic diplegia. As in our previous case,severe red cell GTP depletion - associated with raised dGTP levels and grossly increased NAD levels, were noted. Red cell PP-ribose-P levels and lysate APRT activity were likewise increased. The clinical findings also accord with previous reports. In addition to immunodeficiency, anaemia and neurological complications (ataxia, spastic tetrasparesis) have been reported in 30-40% of cases. The results suggest that patients with severe PNP deficiency may suffer the consequences of two enzyme defects - immunodeficiency due to an inability to metabolise toxic deoxynucleosides plus the neurological complications of hypoxanthine guanine phosphoribosyltransferase (HGPRT) deficiency because of a resultant lack of substrates for the latter. Red cell GTP depletion appears to be a consistent finding in inherited disorders associated with neurodevelopmental retardation.