Partial Hypoxanthine-guanine Phosphoribosyltransferase Research Articles

Clinical symptoms of patients with partial HPRT deficiency.

Since the first description of partial Hypoxanthine-Guanine-Phosphoribosyl-transferase (HPRT) deficiency in 1967 by Kelley, Seegmiller and coworkers a large number of cases has been described. The clinical picture has been quite variable, reaching from asymptomatic hyperuricemia to very severe disease with arthritis, nephrolithiasis and neurological symptoms. In contrast to classical Lesch-Nyhan syndrome selfmutilation is not observed in patients with partial HPRT deficiency.

Partial hypoxanthine-guanine phosphoribosyl transferease deficiency in two Korean siblings?a new mutation

Two Korean siblings with partial hypoxanthine-guanine phosphoribosyltransferase (HPRT) deficiency are reported. The index patient was a boy aged 9 years 10 months who developed acute renal failure with a serum uric acid level of 25.9 mg/dl, after vomiting. The younger brother was asymptomatic but had elevated serum uric acid (9.4 mg/dl). The red blood cell HPRT activity of both siblings was one-tenth of normal. Analysis of genomic DNA revealed a point mutation from A (adenine) to G (guanine) at nucleotide position 215 on exon 3; this is a new mutation. The younger brother had the same mutation and the mother was heterozygous for this mutation.

Gout, uric acid and purine metabolism in paediatric nephrology

Although gout and hyperuricaemia are usually thought of as conditions of indulgent male middle age, in addition to the well-known uricosuria of the newborn, there is much of importance for the paediatric nephrologist in this field. Children and infants may present chronically with stones or acutely with renal failure from crystal nephropathy, as a result of inherited deficiencies of the purine salvage enzymes hypoxanthine-guanine phosphoribosyltransferase (HPRT) and adenine phosphoribosyltransferase (APRT) or of the catabolic enzyme xanthine dehydrogenase (XDH). Genetic purine overproduction in phosphoribosylpyrophosphate synthetase superactivity, or secondary to glycogen storage disease, can also present in infancy with renal complications. Children with APRT deficiency may be difficult to distinguish from those with HPRT deficiency because the insoluble product excreted, 2,8-dihydroxyadenine (2,8-DHA), is chemically very similar to uric acid. Moreover, because of the high uric acid clearance prior to puberty, hyperuricosuria rather than hyperuricaemia may provide the only clue to purine overproduction in childhood. Hyperuricaemic renal failure may be seen also in treated childhood leukaemia and lymphoma, and iatrogenic xanthine nephropathy is a potential complication of allopurinol therapy in these conditions. The latter is also an under-recognised complication of treatment in the Lesch-Nyhan syndrome or partial HPRT deficiency. The possibility of renal complications in these three situations is enhanced by infection, the use of uricosuric antibiotics and dehydration consequent upon fever, vomiting or diarrhoea. Disorders of urate transport in the renal tubule may also present in childhood. A kindred with X-linked hereditary nephrolithiasis, renal urate wasting and renal failure has been identified, but in general, the various rare types of net tubular wasting of urate into the urine are recessive and relatively benign, being found incidentally or presenting as colic from crystalluria. However, the opposite condition of a dominantly inherited increase in net urate reabsorption is far from benign, presenting as familial renal failure, with hyperuricaemia either preceding renal dysfunction or disproportionate to it. Paediatricians need to be aware of the lower plasma urate concentrations in children compared with adults when assessing plasma urate concentrations in childhood and infancy, so that early hyperuricosuria is not missed. This is of importance because most of the conditions mentioned above can be treated successfully using carefully controlled doses of allopurinol or means to render urate more soluble in the urine. Xanthine and 2,8-DHA are extremely insoluble at any pH. Whilst 2,8-DHA formation can also be controlled by allopurinol, alkali is contraindicated. A high fluid, low purine intake is the only possible therapy for XDH deficiency.

The point mutation of hypoxanthine-guanine phosphoribosyltransferase (HPRTEdinburgh) and detection by allele-specific polymerase chain reaction.

The change in DNA responsible for partial hypoxanthine-guanine phosphoribosyltransferase (HPRT) deficiency in three brothers has been determined by polymerase chain amplification and sequencing. An A-to-G substitution at base 155 in exon 3 predicts a change in aspartic acid 52 to glycine. Allele-specific polymerase chain amplification verified the presence of the mutation in genomic DNA and provides a means of direct diagnostic assay.

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.

Carrier Detection of Partial Hypoxanthine-Guanine Phosphoribosyltransferase Deficiency by Analysis with BamHI Restriction Fragment Length Polymorphisms and Oligonucleotide Probes

Hyperuricemic nephropathy can progress to the permanent renal damage even in infancy in partial hypoxanthine-guanine phosphoribosyltransferase (HPRT) deficiency. We have encountered two unrelated patients with partial HPRT deficiency, and found that early detection of the disease and long-term management for hyperuricemia were necessary to prevent renal impairment. The HPRT gene is situated in the q26-27 region of the long arm of the X-chromosome, and females with mutant HPRT alleles are heterozygous for the disease, and they develop gout after menopause. We undertook the investigation of carriers in the two patients' families, using BamHI restriction fragment length polymorphisms and oligonucleotide probes that recognized the specific mutations within the HPRT gene. We also demonstrated that the allele frequencies of BamHI restriction fragment length polymorphisms in 62 Japanese females were 0.36 for the 22-kb/25-kb allele, 0.41 for the 12-kb/25-kb allele, and 0.23 for the 22-kb/18-kb allele, resulting in a heterozygous state in 66% of females.

Bam HI Restriction Fragment Length Polymorphisms for Hypoxanthine‐Guanine Phosphoribosyltransferase (HPRT) Gene of Carriers and Controls of HPRT Deficiency in Japan

Three-allele restriction fragment length polymorphisms (RFLPs) for the restriction endonuclease Bam HI are known at the hypoxanthine-guanine phosphoribosyltransferase (HPRT, E.C.2.4.2.8.) gene locus. The alleles are expressed phenotypically on Southern blots as three distinct pairs of fragments that hybridize to HPRT cDNA: i) a 22-kilobase (kb)/25-kb pair, ii) a 12-kb/25-kb pair, and iii) a 22-kb/18-kb pair. Allele frequencies in 119 unrelated Japanese people were 0.38 for the 22-kb/25-kb allele, 0.43 for the 12-kb/25-kb allele, and 0.19 for the 22-kb/18-kb allele, an average heterozygosity of 66% in Japanese females, a higher rate than in Caucasian females. Five out of nine carriers of partial or complete HPRT deficiency showed heterozygous patterns for Bam HI RFLPs.

Acute Urate Nephropathy Due to Partial Hypoxanthine-Guanine Phosphoribosyl Transferase Deficiency

Acute Urate Nephropathy Due to Partial Hypoxanthine-Guanine Phosphoribosyl Transferase Deficiency

Structural consequences of point mutations in nine human HPRT variants.

Hypoxanthine guanine phosphoribosyltransferase (HPRT) is a purine salvage enzyme responsible for the conversion of hypoxanthine and guanine to IMP and GMP, respectively. A deficiency of HPRT results in two distinct clinical disorders, gout (partial HPRT deficiency) or the Lesch-Nyhan syndrome (complete HPRT deficiency).1, 2

Hypoxanthine-guanine phosphoribosyltransferase. Genetic evidence for identical mutations in two partially deficient subjects.

In past reports of hypoxanthine-guanine phosphoribosyltransferase (HPRT) deficiency a marked degree of molecular heterogeneity has been noted. We have previously described two apparently unrelated subjects with partial HPRT deficiency, G.S. and D.B., who have a mutant form of HPRT with remarkably similar alterations in physical and kinetic properties. The mutation in G.S. is a serine to leucine substitution at amino acid 110 as determined by amino acid sequence analysis. This mutant enzyme has been designated HPRTLondon. We have examined HPRT cDNA from D.B. using two different methods to determine if the similar properties of mutant HPRT from these two subjects are the result of a common mutation. HPRT cDNA clones were obtained by routine cloning techniques and by polymerase chain reaction amplification of single-stranded cDNA reverse transcribed from mRNA derived from subject D.B. Dideoxynucleotide sequencing revealed a single mutation, a C to T transition at bp 329 in clones generated by both methods. This mutation in D.B. predicts the identical amino acid substitution described in HPRTLondon. A C to T nucleotide transition at 329 in D.B. creates an Hpa I site in exon 4 of the HPRT gene. Southern blot analysis of genomic DNA isolated from lymphoblasts derived from G.S. and D.B. revealed that both have this additional Hpa I site, indicating that the similarly altered protein sequence is due to the identical transition in the HPRT gene.

MOLECULAR STUDIES OF HYPOXANTHINE‐GUANINE PHOSPHORIBOSYLTRANSFERASE MUTATIONS IN SIX AUSTRALIAN FAMILIES

Genomic deoxyribonucleic acid (DNA) was isolated from six hemizygotes and five heterozygotes from unrelated families exhibiting the full clinical spectrum of hypoxanthine-guanine phosphoribosyltransferase (HPRT) deficiency. The DNA was digested with the restriction endonucleases, Bam H1, Pst 1 and Taq 1, previously found to be useful in demonstrating restriction fragment length polymorphism (RFLP) at the HPRT locus of the X-chromosome. DNA blotting experiments using a full length HPRT-cDNA probe, have revealed RFLPs in three families which may prove useful for the diagnosis of HPRT deficiency and the determination of heterozygosity. Total ribonucleic acid (RNA) was also extracted from our 11 subjects and analysed by Northern blotting for the presence of HPRT-messenger (mRNA). Apparently normal HPRT-mRNA was demonstrated in all the hemizygotes and heterozygotes for partial HPRT deficiency. In the families with complete HPRT deficiency (Lesch-Nyhan syndrome), the heterozygotes had normal HPRT-mRNA. However, one hemizygote had a complete absence of message for HPRT, while the other hemizygote had considerably reduced amounts of this message.

Molecular Genetics of Hypoxanthine-Guanine Phosphoribosyltransferase Deficiency in Man

Hypoxanthine - guanine phosphoribosyltransferase (HPRT) is a purine salvage enzyme that plays a key role in the regulation of purine metabolism in man. Interest in this X-linked enzyme stems, in part, from the existence of two clinical syndromes associated with deficiency of HPRT enzyme activity. In 1967, Seegmiller et al 1 described a virtually complete deficiency of HPRT activity in patients with the Lesch-Nyhan syndrome. This syndrome is characterized by an overproduction of uric acid as well as a bizarre constellation of neurologic and behavioral abnormalities, including mental retardation, spasticity, choreoathetosis, and a compulsive form of self-mutilation. A partial deficiency of HPRT was subsequently demonstrated in several male patients who presented with hyperuricemia and a severe form of gout at an early age. 2 This latter group of patients is usually free of the central nervous system manifestations that characterize the Lesch-Nyhan syndrome, although an occasional patient with partial HPRT deficiency

Failure to thrive, hyperuricemia, and renal insufficiency in early infancy secondary to partial hypoxanthine-guanine phosphoribosyl transferase deficiency

IlYPERURICEMIA secondary to partial deficiency of the enzyme hypoxanthine-gua nine phosphoribosyl transferase may cause diverse symptoms? .~ Acute renal failure has been precipitated by dehydration and general anesthesia in patients with partial deficiency of HGPRT? 3 Virtual absence of HGPRT is seen with the Lesch-Nyhan syndrome, in which there is severe neurologie impairment in addition to hyperuricemia. We report an infant who had renal insufficiency, failure to thrive, and hyperuricemia at 7 weeks of age who was subsequently demonstrated to have partial deficiency of HGPRT.

Allopurinol-Induced Arteritis in Partial HGPRTase Deficiency

A 17-year-old boy with partial hypoxanthine-guanine phosphoribosyl transferase deficiency developed a hypersensitivity reaction to allopurinol. The reaction was manifested by the development of bizarre, atypical seizures. The patient had been neurologically normal prior to the reaction. Seizures disappeared following discontinuation of allopurinol therapy. Allopurinol apparently can cause a diffuse vasculitis involving cerebral vessels after many year of therapy, resulting in atypical seizures.

An improved method for the determination of 5-phosphoribosyl 1-pyrophosphate

A spectrophotometric method for the determination of 5-phosphoribosyl 1-pyrophosphate (PRPP) is presented which shows several advantages in comparison to the radiochemical techniques, such as a relatively simple, rapid and less expensive procedure. This technique has been used to evaluate PRPP content in erythrocytes, leukocytes and lymphocytes of normal subjects and individuals with partial hypoxanthine guanine phosphoribosyltransferase (EC 2.4.2.8) deficiency. The results obtained proved to be completely reliable in both groups of subjects examined, with values of PRPP similar to those observed by radiochemical techniques.

Abnormal property of human mutant hypoxanthine-guanine phosphoribosyltransferase: insensitivity of fibroblast enzyme to stabilization against freezing and thawing by 5-phosphoribosyl-1-pyrophosphate.

Abstract. Freezing and thawing of dilute normal human fibroblast suspensions causes partial inactivation of hypoxanthine‐guanine phosphoribosyltransferase (HGPRT) and adenine phosphoribosyltransferase (APRT). Phosphoribosyl‐pyrophosphate (PRPP) stabilizes both phosphoribosyltrans‐ferases against this inactivation. Mutant HGPRT enzymes from a patient with the Lesch‐Nyhan syndrome and from a gouty patient with partial HGPRT deficiency were similarly inactivated by freezing and thawing, but only the former mutant enzyme could be stabilized by PRPP. The insensitivity of the mutant HGPRT from the patient with partial enzyme deficiency to PRPP stabilization indicates a structural enzyme alteration. The different sensitivity of the two HGPRT mutants to PRPP stabilization reflects the heterogeneity of HGPRT mutations in man.

Rarity of X-linked partial hypoxanthine-guanine phosphoribosyltransferase deficiency in a large gouty population.

In a survey of 425 cases of hyperuricemia with gouty arthritis or uric acid stone, or both, we found partial deficiency of H-G PRTase, a newly recognized cause of these manifestations, in only 7 subjects, of whom 5 were members of one family. The prevalence in this series was thus 1.6%, which is probably higher than in the gouty population at large because this study included a disproportionately large number of severely afflicted patients. Transmission was through heterozygous, asymptomatic mothers and was expressed only in sons, consistent with X-linkage. Six of the seven hemizygotes detected conformed to previous reports in having very low erythrocyte H-G PRTase activity (about 0.1% to 1% of normal) and increased urinary hypoxanthine to xanthine ratios, usually with relatively early onset of severe symptoms. In the seventh case erythrocyte H-G PRTase activity was about 30% of normal, with an accompanying increase in the urinary hypoxanthine to xanthine ratio. This patient had late onset of moderately severe recurrent gouty arthritis.