Partial HPRT Deficiency Research Articles

Description Kelley-Seegmiller syndrome (partial HPRT deficiency manifesting as a gout-urolithiasis syndrome) in a patient of 15 years old

helix of the right ear, in the angle of the left eye. At the age of 11 there were high levels of uric acid, creatinine and urea. Severe mental disabilities are not present. After conducting genetic study a mutation in the gene Gly15Ser was revealed. The same mutation is found out in mother of the patient and the sister. Diet therapy with allopurinol, blemaren was appointed. In 15 years the patient has chronic polyarthritis including of small joints of hands and feet, knees and has spread tophuses. X-ray study has shown the destructive changes of the affected joints. Ultrasound study of kidneys has shown the symptoms of nephrolithiasis. Scintigraphy has shown the decrease in the total volume of functioning parenchyma and diffuse-focal changes of kidneys. Blood test revealed elevated levels of uric acid, creatinine, urea. Uric acid level is controlled by allopurinol therapy. Figures 1 and 2. * Correspondence: rodionovskaya@mail.ru Children’s Hospital No38 Federal Medical Biological Agency of Russia, Moscow, Russia Full list of author information is available at the end of the article Figure 1 Figure 2 Rodionovskaya et al. Pediatric Rheumatology 2011, 9(Suppl 1):P33 http://www.ped-rheum.com/content/9/S1/P33

Fenotipo variante del síndrome de Lesch-Nyhan

Background and objective Lesch-Nyhan syndrome (LNS) and LNS variants are due to mutations in the HPRT1 gene causing HPRT enzymatic activity deficiency. We report a patient presenting a variant phenotype and a major genetic defect. The mutation has been previously reported as always associated with complete Lesch-Nyhan phenotype. Patient and methods We analyzed the presence of complete HPRT mRNA in this patient, in two patients with the complete Lesch Nyhan syndrome phenotype, and in control subjects. Results We found a minor amount of normal HPRT mRNA in the present patient but also in the two patients with splice mutation and the complete Lesch Nyhan syndrome phenotype. Conclusions To our knowledge, this patient is the first report of a major genetic defect, with no detectable enzymatic activity, and a partial HPRT deficiency phenotype. Our results question the hypothesis of a normally spliced HPRT cDNA as the sole cause of the patient partial phenotype.

Hypoxanthine‐guanine phosphoribosylotransferase deficiency—The spectrum of Polish mutations

Hypoxanthine-guanine phosphoribosyltransferase (HPRT; EC 2.4.2.8) deficiency (OMIM 308000) is an inborn error of purine metabolism. The defect causes three overlapping clinical syndromes: Lesch-Nyhan disease (LND; OMIM 300322), HPRT-related hyperuricaemia with neurologic dysfunction (HRND) and hyperuricaemia alone (HRH; OMIM 300322). During the period 1977-2007, 18 patients belonging to 12 Polish families and one Latvian family with HPRT deficiency have been identified. The majority of patients had a typical LND phenotype, three patients were classified as HRH and one patient as an intermediate phenotype (HRND). Genetic analysis revealed 12 different HPRT1 mutations, five of them being unique. In two typical Lesch-Nyhan families a novel single-base substitution, c.220T>G (p.Phe74Val), and a deletion of seven nucleotides, c.395_401del7 (p.Ile132LysfsX3), were found. Another novel single-base substitution, c.295T>G (p.Phe99Val), was identified in a patient with severe partial deficiency of HPRT with neurological dysfunction. In patients belonging to the HRH group, two transitions were detected: c.481G>A (p.Ala161Thr) and c.526C>T (p.Pro176Ser). Other mutations identified in Polish patients, c.131A>G (p.Asp44Gly), c.222C>A (p.Phe74Leu), c.385-1G>A (p.Asn129_Glu134del), c.482C>A (p.Ala161Glu), c.508C>T (p.Arg170Ter) and c.569G>A (p.Gly190Glu), have been reported previously in unrelated patients and are located within one of the clusters of hot spots of the HPRT1 gene (exons 3, 7 and 8). Patients with partial phenotypes presented mutations predicted to permit some degree of residual enzyme function (single-base substitutions). All mutations, except c.508C>T (p.Arg170Ter), were found in single families only, indicating the lack of any common mutation causing HPRT deficiency in Poland.

Urinary Guanidinoacetate and Creatine Levels in Patients with HPRT Deficiency

Neurobehavioral manifestations of complete HPRT deficiency include severe action dystonia, choreathetosis, alteration of executive functions, and self-injurious behavior. Dystonic manifestations are also present in patients with partial HPRT deficiency. Pathophysiology of these manifestations is unknown. Guanidinoacetate is a neurotoxin implicated in certain dystonic syndromes. We have examined guanidinoacetate and creatine levels in urine from 11 HPRT deficient patients (9 with Lesch-Nyhan syndrome and 2 with partial deficiency). Urinary guanidinoacetate and creatine levels in HPRT deficient patients were within the normal range. Guanidinoactetate alteration does not seem to be implicated in the pathogenesis of the neurological disease associated with HPRT deficiency.

The Diagnosis Of HPRT Deficiency in the 21St Century

We have studied 36 patients with HPRT deficiency, 25 with Lesch-Nyhan syndrome and 11 with partial HPRT deficiency (grades 1 to 3). Patients diagnosed with HPRT deficiency have increased 50% since 2000. The most relevant recent advances have been made in molecular diagnosis. Nevertheless, enzyme determinations are still essential for the diagnosis of HPRT deficiency. Therapy for the neurological manifestations of HPRT deficiency has not advanced. Allopurinol remains the drug of choice to diminish uric acid overproduction, but the optimal allopurinol dose must be established in each patient to prevent xanthine or uric acid urolithiasis, a process aided by sequential determination of urinary oxypurines and uric acid.

Molecular analysis of HPRT deficiencies: An update of the spectrum of Asian mutations with novel mutations

Inherited mutations of a purine salvage enzyme, hypoxanthine guanine phosphoribosyltransferase (HPRT, EC 2.4.2.8), give rise to Lesch–Nyhan syndrome or HPRT-related gout. We have identified a number of HPRT mutations in Asian patients manifesting different clinical phenotypes, by analyzing all nine exons of the HPRT gene ( HPRT1) from genomic DNA and reverse-transcribed mRNA using the PCR technique coupled with direct sequencing. In this study, we update the spectrum of mutations with nine novel mutations. Two missense mutations (T124P and D185G) were detected in patients with HRH (HPRT-related hyperuricemia). In a patient having a severe partial deficiency of HPRT with neurological dysfunction (HRND: HPRT-related neurological dysfunction), a single nucleotide substitution (27 + 5G > A) causing a splicing error was found in intron 1. The mutation resulted in a remarkably decreased level of normal mRNA, and production of an abnormal mRNA with a 49-bp insert at the 5′-end of intron 1, which caused the frame-shift of an amino acid codon (10fs27X). In six typical Lesch–Nyhan families, we found two 3-bp deletions responsible for single amino acid deletions (V8del and Y28del), two 1-bp deletions (440delA and 635delG) generating a frame-shift, an insertion of two amino acids (159insKV), and a 4,131-bp deletion from introns 4 to 6 resulting in two types of abnormal mRNA. Including these nine mutations, 42 HPRT1 mutations have been identified among 47 Asian families with deficiency of HPRT.

Efficacy and Safety of Allopurinol in Patients with the Lesch-Nyhan Syndrome and Partial Hypoxanthine- Phosphoribosyltransferase Deficiency: a Follow-up Study of 18 Spanish Patients

Allopurinol is used widely for the treatment of purine disorders such as gout, but efficacy and safety of allopurinol has not been analyzed systematically in an extensive series of patients with HPRT deficiency. From 1984 to 2004 we have diagnosed 30 patients with HPRT deficiency. Eighteen patients (12 with Lesch-Nyhan syndrome or complete HPRT deficiency, and 6 with partial HPRT deficiency) were treated with allopurinol (mean dose, 6.44 mg/Kg of weight per day) and followed-up for at least 12 months (mean follow-up 7,6 years per patient). Mean age at diagnosis was 7 years (range, 5 months to 35 years). Treatment with allopurinol was associated to a mean reduction of serum urate concentration of 50%, and was normalized in all patients. Mean urinary uric acid excretion was reduced by 75% from baseline values, and uric acid to creatinine ratio was close or under 1.0 in all patients. In contrast, hypoxanthine and xanthine urinary excretion rates increased by a mean of 6 and 10 times, respectively, compared to baseline levels. These modifications were similar in patients with complete or partial HPRT deficiency. In 2 patients xanthine stones were documented despite allopurinol dose adjustments to prevent markedly increased oxypurine excretion rates. Neurological manifestations did not appear to be influenced by allopurinol therapy. Allopurinol is a very efficacy and fairly safety drug for the treatment of uric acid overproduction in patients with complete and partial HPRT deficiency. Allopurinol was associated with xanthine lithiasis.

Neurocognitive functioning in Lesch-Nyhan disease and partial hypoxanthine-guanine phosphoribosyltransferase deficiency.

Lesch-Nyhan disease (LND) is a rare, X-linked genetic disorder that involves the nearly complete absence of an enzyme (hypoxanthine-guanine phosphoribosyltransferase, or HPRT) that is essential for purine salvage. In addition to hyperuricemia, all patients with classic LND suffer from movement disorder and compulsive self-injury, and most have mental retardation. Patients with partial HPRT deficiency (variants) always have hyperuricemia and often have neurologic abnormalities, but do not self-injure and usually are described as having normal intelligence. Here we compare 15 patients with LND to 9 variants and 13 normal adolescents and adults. Testing revealed unambiguous and qualitatively similar cognitive deficits in both patient groups. The variants produced scores that were intermediate between those of patients with LND and normal participants on nearly every cognitive measure. We discuss these findings in terms of what is known about the neuropathology of LND.

Novel genetic mutations responsible for the HPRT deficiency and the clinical phenotypes in Japanese.

ConclusionWe have identified six novel mutations in Japanese families of HPRT deficiency manifesting different clinical phenotypes. A missense mutation (Y195C) was identified in a patient with hyperuricemia and gout (Case 1). In Cases 2 and 3 with mild neurological symptoms, missense mutations L147P and K159E were detected, respectively. A point mutation 532+2T>C causing splicing error was found in a severe form of partial HPRT deficiency (Case 4). Two mutations causing splicing error, 609+1delGT (Case 5) and 610-−1G>A (Case 6), resulted in the classic Lesch-Nyhan syndrome.

Enzyme activities leading to NAD synthesis in the erythrocytes of HPRT deficient subjects.

The relationship between HPRT deficiency and the devastating neurologic dysfunction in Lesch-Nyhan syndrome is still unknown. Different metabolic alterations have been found, mainly in the erythrocytes, which could suggest involvement of different metabolic pathways; one of the described alterations is the high NAD level reported in patients with partial or total HPRT deficiency.1 Whether NAD increase can contribute to the clinical features is not known, but due to the peculiar role played by this coenzyme, it is reasonable that its alteration may be reflected on various metabolic aspects. In order to understand the mechanisms causing NAD raised concentrations, we have looked for possible increase in the stability, which was demonstrated not to be altered in patient erythrocytes.2 Possible alterations of NAD synthesis were thus hypothesized and “in vitro” incorporation of NAD precursors by intact erythrocytes was studied, demonstrating altered regulation in patients with partial or total deficiency.3 In the present study we have assayed the enzyme activities of the so-called deamidated pathway, starting from nicotinic acid, i.e. nicotinate phosphoribosyl transferase (NAPRT), nicotinate mononucleotide adenylyltransferase (NAMN-AT) and NAD synthetase (NADs), in order to ascertain the involvement of the committed enzymes leading to NAD synthesis. The possible effect of endogenous compounds and the heat resistance of the enzyme activities in crude lysates has also been examined in controls and patients.KeywordsNicotinic AcidEndogenous CompoundPerchloric Acid ExtractionPeculiar RoleHPRT DeficiencyThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Prenatal diagnosis of HPRT mutant genes in Lesch-Nyhan syndrome.

Lesch-Nyhan syndrome is an X-linked recessive disorder characterized by hyperuricemia, physical and mental retardation, choreoathetosis, and compulsive self-mutilation.1 This disease is associated with the complete absence of activity of an enzyme involved in purine metabolism, hypoxanthine guanine phosphoribosyltransferase (HPRT, EC 2.4.2.8).2 Partial HPRT deficiency generally presents as gout and uric acid overproduction in early adulthood.3 The marked genetic heterogeneity of HPRT deficiency is well known. As reviewed previously by Sculley et al.,4 many different mutations at the HPRT gene locus (deletions, insertions, duplications, abnormal splicing, and point mutations at different sites of the coding region from exon 1 to 9) have been reported. We have identified Japanese and Korean HPRT mutants,5–12 including two rare cases in female subjects,5,9 by polymerase chain reaction of reverse-transcribed mRNA (RT-PCR) and the multiplex amplification technique of all nine HPRT exons from the genomic DNA coupled with direct sequencing. In this study, we report prenatal diagnoses of HPRT mutant genes which have been carried out in five Lesch-Nyhan families.

Phenotype and genotype in partial HPRT deficiency

Phenotype and genotype in partial HPRT deficiency

Enzyme activities leading to NAD synthesis in the erythrocytes of HPRT deficient subjects

The relationship between HPRT deficiency and the devastating neurologic dysfunction in Lesch-Nyhan syndrome is still unknown. Different metabolic alterations have been found, mainly in the erythrocytes, which could suggest involvement of different metabolic pathways; one of the described alterations is the high NAD level reported in patients with partial or total HPRT deficiency.1 Whether NAD increase can contribute to the clinical features is not known, but due to the peculiar role played by this coenzyme, it is reasonable that its alteration may be reflected on various metabolic aspects. In order to understand the mechanisms causing NAD raised concentrations, we have looked for possible increase in the stability, which was demonstrated not to be altered in patient erythrocytes.2 Possible alterations of NAD synthesis were thus hypothesized and “in vitro” incorporation of NAD precursors by intact erythrocytes was studied, demonstrating altered regulation in patients with partial or total deficiency.3 In the present study we have assayed the enzyme activities of the so-called deamidated pathway, starting from nicotinic acid, i.e. nicotinate phosphoribosyl transferase (NAPRT), nicotinate mononucleotide adenylyltransferase (NAMN-AT) and NAD synthetase (NADs), in order to ascertain the involvement of the committed enzymes leading to NAD synthesis. The possible effect of endogenous compounds and the heat resistance of the enzyme activities in crude lysates has also been examined in controls and patients.

Prenatal diagnosis of HPRT mutant genes in Lesch-Nyhan syndrome

Lesch-Nyhan syndrome is an X-linked recessive disorder characterized by hyperuricemia, physical and mental retardation, choreoathetosis, and compulsive self-mutilation.1 This disease is associated with the complete absence of activity of an enzyme involved in purine metabolism, hypoxanthine guanine phosphoribosyltransferase (HPRT, EC 2.4.2.8).2 Partial HPRT deficiency generally presents as gout and uric acid overproduction in early adulthood.3 The marked genetic heterogeneity of HPRT deficiency is well known. As reviewed previously by Sculley et al.,4 many different mutations at the HPRT gene locus (deletions, insertions, duplications, abnormal splicing, and point mutations at different sites of the coding region from exon 1 to 9) have been reported. We have identified Japanese and Korean HPRT mutants,5–12 including two rare cases in female subjects,5,9 by polymerase chain reaction of reverse-transcribed mRNA (RT-PCR) and the multiplex amplification technique of all nine HPRT exons from the genomic DNA coupled with direct sequencing. In this study, we report prenatal diagnoses of HPRT mutant genes which have been carried out in five Lesch-Nyhan families.

Characterization of mutations in phenotypic variants of hypoxanthine phosphoribosyltransferase deficiency.

The Lesch-Nyhan disease is caused by an almost complete lack of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT). Partial HPRT-deficiency, associated with less severe phenotype, has also been identified. We have characterized mutations occurring in HPRT cDNA isolated from patients with HPRT-deficiency with an emphasis on examining the more unusual partial variants of HPRT-deficiency. HPRT cDNA was amplified by PCR, cloned and analyzed by automated DNA sequence analysis. Twenty-two, unrelated individuals with HPRT deficiency were studied including eight classic Lesch-Nyhan patients and fourteen patients representing the different groups of partial HPRT deficiency. We found a diverse pattern of mutations with point mutations accounting for the majority of abnormal HPRT genes. Nonsense mutations and exon deletions were only found in HPRT cDNA isolated from classic Lesch-Nyhan patients. Mutations associated with partial HPRT-deficiency were frequently located in the amino terminal part of the molecule. A CpG mutational hot spot was identified at the position for Arg-51 in the HPRT protein. Two hyperuricemic patients exhibited unusual splice site mutations: in one this led to the creation of an additional exon in the HPRT gene and in the other part of exon 6 was missing in a subpopulation of the transcripts, producing the effect of a dominant, negative mutation.

Purine Synthesis de novo and Salvage in Hypoxanthine Phosphoribosyltransferase-Deficient Mice

Extreme degrees of hypoxanthine phosphoribosyltransferase (HPRT) deficiency in man are associated with gross sex-linked neurological dysfunction, gout and urinary stones (the Lesch-Nyhan or 'complete HPRT-deficiency' syndrome). The less severe degrees of enzyme deficiency (sex-linked recessive gout and/or urolithiasis or the 'partial HPRT-deficiency' syndrome) may be associated with minor neurological manifestations. Whole body purine synthesis de novo is accelerated in both these groups of patients. A strain of mice with an experimentally produced mutation at the HPRT locus showed some residual 'apparent HPRT activity' in brain, liver, testicular, splenic, kidney and ovarian tissues but not in erythrocyte haemolysates. The mutation removes exons 1 and 2 of the coding region of the gene together with the promotor and about 10 kb of upstream sequence from the gene. It is therefore possible that the observed 'apparent HPRT activity' in these mice is due to the operation of an alternative metabolic pathway. Purine synthesis de novo was markedly accelerated in their brain, testicular, splenic and kidney tissues. It was not accelerated in the liver tissue of male mice hemizygous for the mutation and the degree of acceleration in the female homozygotes only just reached statistical significance at the p = 0.02 level. This observation casts doubt on the importance of modulations in the rate of hepatic purine synthesis de novo as a mechanism for maintaining a steady supply of purines for translocation to other organs.

Identification of a single nucleotide substitution in the coding sequence ofin vitro amplified cDNA from a patient with partial HPRT deficiency (HPRTBrisbane)

The change in genomic DNA responsible for HPRT deficiency has been determined in a patient with urate overproduction and gout. In erythrocyte cell lysates, this patient had approximately 10% of normal HPRT enzyme activity and 26% of immunoidentical HPRT protein. Cultured lymphoblasts derived from this patient were used to extract mRNA. This was reverse transcribed to cDNA, which was then amplified using the polymerase chain reaction. The resulting DNA was cloned and the nucleotide sequence determined. In addition a portion of the sequence was derived from cloned double-stranded cDNA prepared by conventional first and second strand synthesis. A single nucleotide base change (a C----T transition) was detected, which predicts an amino acid substitution of isoleucine for threonine at amino acid 168 of the HPRT protein. The nucleotide substitution creates a BamHI site, confirming a restriction fragment length polymorphism previously reported in this patient.

Purine synthesis de novo and salvage in hypoxanthine phosphoribosyltransferase-deficient mice

Extreme degrees of hypoxanthine phosphoribosyltransferase (HPRT) deficiency in man are associated with gross sex-linked neurological dysfunction, gout and urinary stones (the Lesch-Nyhan or 'complete HPRT-deficiency' syndrome). The less severe degrees of enzyme deficiency (sex-linked recessive gout and/or urolithiasis or the 'partial HPRT-deficiency' syndrome) may be associated with minor neurological manifestations. Whole body purine synthesis de novo is accelerated in both these groups of patients. A strain of mice with an experimentally produced mutation at the HPRT locus showed some residual 'apparent HPRT activity' in brain, liver, testicular, splenic, kidney and ovarian tissues but not in erythrocyte haemolysates. The mutation removes exons 1 and 2 of the coding region of the gene together with the promotor and about 10 kb of upstream sequence from the gene. It is therefore possible that the observed 'apparent HPRT activity' in these mice is due to the operation of an alternative metabolic pathway. Purine synthesis de novo was markedly accelerated in their brain, testicular, splenic and kidney tissues. It was not accelerated in the liver tissue of male mice hemizygous for the mutation and the degree of acceleration in the female homozygotes only just reached statistical significance at the p = 0.02 level. This observation casts doubt on the importance of modulations in the rate of hepatic purine synthesis de novo as a mechanism for maintaining a steady supply of purines for translocation to other organs.

Molecular Analysis of Hypoxanthine‐Guanine Phosphoribosyltransferase Mutations in Five Unrelated Japanese Patients

The isoenzyme of hypoxanthine-guanine phosphoribosyltransferase (HPRT, E.C.2.4.2.8) functions in the metabolic salvage of purines. Partial HPRT deficiency is associated with gouty arthritis, while absence of activity results in Lesch-Nyhan (LN) syndrome. We characterized five unrelated patients with HPRT deficiency to understand the spectrum of molecular defects using Southern and Northern blot, polymerase chain amplification of HPRT mRNA and DNA sequencing, and oligonucleotide hybridization analysis of the HPRT gene. Southern blot analysis of DNA indicated that mutations leading to HPRT deficiency in our five patients were not the result of major chromosomal rearrangements or deletions. Sequencing analysis of the amplified DNA from three different patients with HPRT deficiency implied three unique molecular abnormalities: 1) one single-base substitution at codon 54 (from ATG to CTG) resulting in the replacement of methionine with leucine in an LN patient, 2) two single-base substitutions at codon 179 (from GTT to GGT) and at codon 180 (from GGA to AGA) resulting in the replacement of valine with glycine and glycine with arginine in a gouty patient, and 3) 51 nucleotide deletion between nucleotides 747 and 797 resulting in the formation of shorter sized HPRT mRNA and putative two amino-acid deleted HPRT protein in another gouty patient. These results are the direct molecular evidence of genetic heterogeneity in mutant HPRT.

Restriction fragment length polymorphisms of HPRT and APRT genes in Japanese population.

HPRT and APRT are the enzymes of salvage pathway in purine metabolism. A deficiency of HPRT is associated with two clinical syndrome in human. A virtually complete deficiency of the enzyme occurs in patient with Lesch-Nyhan syndrome 1, 2 and a partial deficiency of HPRT in severe form of gout.3 APRT enzyme deficiency is a relatively rare, autosomal reccesive disease. Homozygous affected individuals display elevated levels of adenine and its oxidized derivatives 8-hydroxyadenine and 2, 8-dihydroxyadenine leading to urolithiasis and renal failure.4 KeywordsRestriction Fragment Length PolymorphismJapanese PopulationHypoxanthine PhosphoribosyltransferaseLocus AlleleAdenine PhosphoribosyltransferaseThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.