H. Anne Simmonds

Complete deficiency of adenine phosphoribosyltransferase. Report of a family.

We studied the clinical and biochemical manifestations of complete adenine phosphoribosyltransferase deficiency in the kindred of a male homozygous child excreting stones of 2,8-dihydroxyade-nine. Abnormal amounts of adenine, 8-hydroxyade-nine and 2,8-dihydroxyadenine (25 per cent of total purine metabolites) appeared in the urine of the propositus and his clinically normal brother, but not in heterozygotes or a control. Adenine phosphoribosyl-transferase activity in erythrocytes was less than 1 per cent of normal in both homozygotes and varied from 20 to 57 per cent of normal in six heterozygotes. Heterozygotes exhibited neither hyperuricemia nor gout. Treatment of the propositus with allopurinol and a low purine diet stopped stone formation. In addition, excretion of 2,8-dihydroxyadenine decreased. An autosomal recessive mode of inheritance with variable expression in the phenotype is indicated. Homozygotes may be detected by their raised urinary adenine levels or absence of detectable erythrocyte adenine phosphoribosyltransferase activity (or both).

Demonstration of a combined deficiency of xanthine oxidase and aldehyde oxidase in xanthinuric patients not forming oxipurinol

Genetic heterogeneity has been suggested in xanthinuria from the hitherto unexplained ability of some patients with this hereditary disorder to convert allopurinol to its active metabolite oxipurinol--an activity generally attributed to xanthine oxidase. This study provides evidence that the enzyme aldehyde oxidase is also deficient in xanthinuric patients not converting allopurinol to oxipurinol, whereas a xanthinuric patient with normal formation of oxipurinol had normal aldehyde oxidase activity. It is concluded that the enzyme aldehyde oxidase is the principal enzyme responsible for the formation of oxipurinol in man.

Inherited superactivity of phosphoribosylpyrophosphate synthetase: Association of uric acid overproduction and sensorineural deafness

PURPOSE Superactivity of 5-phosphoribosyl 1-pyrophosphate (PP-Rib-P) synthetase, inherited as an X chromosome-linked trait, has been reported in nearly 20 families in which overproduction of uric acid is invariably present in hemizygous affected males. Clinical manifestations of PP-Rib-P synthetase superactivity are mainly limited to gout in early adulthood. Neurologic deficits, including sensorineural deafness, have rarely been described. We herein document the association of PP-Rib-P synthetase superactivity, gout with excessive uric acid synthesis, and sensorineural deafness in an additional family. PATIENTS AND METHODS Two members of a Spanish family were studied: an eight-year-old boy (Patient 1) with tophaceous gout, purine nucleotide and uric acid overproduction, and sensorineural deafness, and his 27-year-old mother (Patient 2), who had gout. Fibroblast cultures were initiated from skin biopsy specimens, and measurements of PP-Rib-P and purine nucleotide metabolism in the fibroblasts were performed. RESULTS A labile but superactive PP-Rib-P synthetase was demonstrated in the fibroblasts cultured from both Patients 1 and 2. The kinetic basis of PP-Rib-P synthetase superactivity in this family was resistance to purine nucleotide inhibition of enzyme activity. More severe derangements in the enzyme and in PP-Rib-P and purine synthesis in Patient 1s cells than in Patient 2s cells suggest that Patient 1 is hemizygous and Patient 2 is heterozygous for an X chromosome-linked genetic defect. Limited pedigree data support this view. Compared with affected members of seven other families with PP-Rib-P synthetase superactivity, these patients are intermediate in the range of clinical expression and in the severity of the enzyme defect as measured by the degree of aberration of PP-Rib-P and purine nucleotide synthesis in fibroblasts. Metabolic abnormalities were more severe in Patient 1s cells than in the cells of most male patients (in whom clinical expression is limited to early adult-onset gout) but were less severe than in the cells of two patients in whom more complex enzyme defects were associated with uric acid overproduction and neurodevelopmental abnormalities (including deafness) in male children and adult women. CONCLUSION Certain defects resulting in PP-Rib-P synthetase superactivity may be causally related to neurologic impairment, most commonly sensorineural deafness.

Urinary excretion of purines, pyrimidines and pyrazolopyrimidines in patients treated with allopurinol or oxipurinol

Abstract When allopurinol was administered to three patients with good renal function, two suffering from gout and one a xanthinuric, the metabolites recovered in the urine (76% of the dose) consisted of oxipurinol (73.6%), allopurinol (10.4%), allopurinol riboside (12.5%) and oxipurinol riboside (3.5%). Only 36% of an equivalent dose of oxipurinol was recovered daily from the urine of the same patients, chiefly in the form of unchanged oxipurinol (94.6%), the remainder being oxipurinol riboside. In the two gouty patients the urinary excretion of xanthine and hypoxanthine was increased during drug treatment and the ratio of xanthine to hypoxanthine excreted was markedly altered. Prior to treatment these two patients had a xanthine/hypoxanthine ratio of 0.68 which increased to 4.15 on allopurinol and 1.75 on oxipurinol. The xanthine/hypoxanthine ratio in the patient with xanthinuria was approximately 5 and not markedly altered throughout the study. In all three patients the pattern of excretion of other urinary purines was not altered by treatment with allopurinol or oxipurinol. A dietary origin is suggested for 1-methylxanthine, 7-methylxanthine and 5-acetylamino-6-amino-3-methyluracil since these compounds were not excreted when purine intake was restricted. The excretion of pseudouridine was excessive in two patients, irrespective of diet. A remarkable finding in these two patients was the replacement of urinary pseudouridine by an equivalent amount of uracil during separate periods of several consecutive days.

Presymptomatic detection of familial juvenile hyperuricaemic nephropathy in children

Abstract. We studied 34 apparently healthy children and 2 propositi from kindreds with familial juvenile hyperuricaemic nephropathy (FJHN) – a disorder characterised by early onset, hyperuricaemia, gout, familial renal disease and a similarly low urate clearance relative to glomerular filtration rate (GFR) [fractional excretion of uric acid (FEur) 5.1±1.6%] in young men and women. In addition to the propositi, 17 asymptomatic children were hyperuricaemic – mean plasma urate (368±30 μmol/l), twice that of controls (154±41 μmol/l). Eight of them had a normal GFR (>80 ml/min per 1.73 m2), and 11 renal dysfunction, which was severe in 5. The FEur in the 14 hyperuricaemic children with a GFR >50 ml/min was 5.0±0.5% and in the 5 with a GFR ≤50 ml/min was still low (11.5±0.2%) compared with controls (18.4±5.1%). The 17 normouricaemic children (185±37 μmol/l) had a normal GFR (>80 ml/min) and FEur (14.0±5.3%). The results highlight the dominant inheritance, absence of the usual child/adult difference in FEur in FJHN and presence of hyperuricaemia without renal disease in 42% of affected children, but not vice versa. Since early allopurinol treatment may retard progression to end-stage renal failure, screening of all relatives in FJHN kindreds is essential.

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.

Severe pyridine nucleotide depletion in fibroblasts from Lesch-Nyhan patients.

The relationship between a complete deficiency of the purine enzyme hypoxanthine-guanine phosphoribosyltransferase and the neurobehavioural abnormalities in Lesch-Nyhan disease remains an enigma. In vitro studies using lymphoblasts or fibroblasts have evaluated purine and pyrimidine metabolism with conflicting results. This study focused on pyridine nucleotide metabolism in control and Lesch-Nyhan fibroblasts using radiolabelled salvage precursors to couple the extent of uptake with endocellular nucleotide concentrations. The novel finding, highlighted by specific culture conditions, was a marked NAD depletion in Lesch-Nyhan fibroblasts. ATP and GTP were also 50% of the control, as reported in lymphoblasts. A 6-fold greater incorporation of [(14)C]nicotinic acid into nicotinic acid- adenine dinucleotide by Lesch-Nyhan fibroblasts, with no unmetabolized substrate (20% in controls), supported disturbed pyridine metabolism, NAD depletion being related to utilization by poly(ADP-ribose) polymerase in DNA repair. Although pyrimidine nucleotide concentrations were similar to controls, Lesch-Nyhan cells showed reduced [(14)C]cytidine/uridine salvage into UDP sugars. Incorporation of [(14)C]uridine into CTP by both was minimal, with more than 50% [(14)C]cytidine metabolized to UTP, indicating that fibroblasts, unlike lymphoblasts, lack active CTP synthetase, but possess cytidine deaminase. Restricted culture conditions may be neccesary to mimic the situation in human brain cells at an early developmental stage. Cell type may be equally important. NAD plus ATP depletion in developing brain could restrict DNA repair, leading to neuronal damage/loss by apoptosis, and, with GTP depletion, affect neurotransmitter synthesis and basal ganglia dopaminergic neuronal systems. Thus aberrant pyridine nucleotide metabolism could play a vital role in the pathophysiology of Lesch-Nyhan disease.

GTP depletion and other erythrocyte abnormalities in inherited pnp deficiency

GTP levels were low and NAD+ levels high in purine nucleoside phosphorylase (PNP) deficient erythrocytes, in addition to the raised deoxy-GTP (dGTP) levels previously noted by others. dGTP was also identified in the PNP deficient childs lymphocytes. A further novel finding was the conversion of hypoxanthine to inosine by the PNP deficient red cells, as compared to inosine monophosphate (IMP) in controls. This has been attributed to IMP formation with subsequent breakdown, and raises interesting questions regarding the controls which normally maintain erythrocyte nucleotide pools. These findings may also explain the gross purine overproduction seen in this defect; they may likewise be related to the associated immunodeficiency, anaemia, and other clinical manifestations. The results may also have important implications for the development and clinical use of PNP inhibitors.

Molybdenum cofactor deficiency – phenotypic variability in a family with a late‐onset variant

In a family with molybdenum cofactor deficiency, the onset in the index case was delayed until 1 year of age, when the patient presented with an episode of lethargy and inconsolable crying culminating in a seizure. By 17 months she showed mild motor delay, regression in language skills, and feeding difficulties. Progressive global deterioration followed, associated with sustained irritability, dystonic posturing, and further seizures, before her condition subsequently plateaued. Low plasma uric acid, raised urinary xanthine and hypoxanthine, and positive urinary sulphite were found, which, coupled with assay of sulphite oxidase activity in cultured fibroblasts, confirmed the diagnosis. A sibling had isolated lens dislocation and an identical biochemical profile. MRI in both children was strikingly abnormal. Molybdenum cofactor deficiency may present as a late‐onset variant with considerable phenotypic variability.

Two dimensional thin-layer high-voltage electrophoresis and chromatography for the separation of urinary purines, pyrimidines and pyrazolopyrimidines

Abstract A method, which is both rapid and quantitative, is described for the separation of purines, pyrimidines, and pyrazolopyrimidines by two dimensional thin-layer high-voltage electrophoresis and chromatography, following anion exchange. The observed electrophoretic and Chromatographie mobilities, as well as the spectral data calculated for these bases from the behaviour of authentic compounds in the three systems, have been tabulated. The experimental conditions necessary to ensure the reproducibility of the method are defined.