Metabolite monitoring to guide thiopurine therapy in systemic autoimmune diseases

6-Thioguanine nucleotide (6-TGN) is the active metabolite of thiopurine drugs azathioprine and 6-mercaptopurine. 6-Methylmercaptopurine (6-MMP) is an inactive and potentially hepatotoxic metabolite. A subgroup of patients (shunters) preferentially produce 6-MMP instead of 6-TGN, therefore displaying thiopurine resistance and risk for hepatotoxicity. Outside inflammatory bowel disease literature, few data exist regarding individualized thiopurine therapy based on metabolite monitoring. This study sought to describe metabolite monitoring in patients receiving weight-based thiopurine for systemic autoimmune diseases. Patients were enrolled using a laboratory database, and data were retrospectively collected. The correlation between the highest thiopurine dose (mg/kg) and the 6-TGN concentration (pmol/8 × 10⁸ erythrocytes) was estimated with Pearson's correlation coefficient. Seventy-one patients with various systemic autoimmune conditions were enrolled. The correlation between the thiopurine dose and the 6-TGN level was weak for the overall patient sample (r = 0.201, p = 0.092) and for the subgroup of non-shunters (r = 0.278, p = 0.053). Subjects with 6-MMP levels >5700 pmol/8 × 10⁸ erythrocytes had more hepatic cytolysis compared to subjects with 6-MMP <5700, OR = 4.36 (CI 95% 1.18-16.13, p = 0.027). Twenty-two patients (31%) were identified as shunters. Six shunters developed hepatotoxicity, five of which had 6-MMP concentration >5700. Eleven non-shunters had hepatotoxicity, one of which had 6-MMP >5700. Thiopurine metabolite monitoring shows wide variability in 6-TGN levels among patients treated with weight-based thiopurine for systemic autoimmune diseases. Thirty-one percent of the patients in our series fulfilled the shunter definition. Thiopurine metabolite monitoring and dose adjustment to improve maintenance of remission and avoid hepatotoxicity should be studied prospectively.

Autoimmune hepatitis with sclerosing cholangitis in a patient with thiopurine methyltransferase deficiency: case presentation

The association between two autoimmune diseases is known in the literature as overlap syndrome. We present the case of an 18-year-old boy, diagnosed at the age of 13 with an overlap syndrome between type I autoimmune hepatitis and sclerosing cholangitis. The response to immunosuppressant therapy was hampered by azathioprine-induced toxicity causing severe pancytopenia, as a result of thiopurine methyltransferase enzyme genetic deficiency. Treatment was replaced by mycophenolate mofetil. Although the relapse rate was reduced, the disease progressed to cirrhosis. Specific features of this case were the overlap syndrome, young age of onset, especially for sclerosing cholangitis, azathioprine toxicity that influenced the prognosis and the treatment problems regarding the use and efficiency of alternative immunosuppressant agents in pediatric patients.

A diagnostic approach to recurrent myalgia and rhabdomyolysis in children

Episodic myalgia is a common complaint in children and young adults. While many cases remain idiopathic even after extensive investigation, myalgia can be the first symptom of an underlying serious neuromuscular condition, and can be associated with an increased risk of such serious complications as rhabdomyolysis and malignant hyperthermia. We review and highlight the metabolic myopathies and other increasingly recognised muscle disorders that may present to paediatricians with episodic myalgia or isolated episodes of rhabdomyolysis, and propose a diagnostic algorithm for investigation of these complaints.

[Asymptomatic classical hereditary xanthinuria type 1]

We report on a girl who was diagnosed with classical hereditary xanthinuria due to an incidental finding of extremely low Levels of uric acid in the blood. The girl is compLetely asymptomatic. Hereditary xanthinuria is a rare autosomal recessive disease that usually causes early urolithiasis but may cause rheumatoid arthritis-like disease and even be associated with defects in the formation of bone, hair and teeth. In Israel it has mostly been described in patients of Bedouin origin. Throughout the world, only about 150 cases have been described; about two thirds of these patients were asymptomatic. Since the clinical presentation and age of symptom appearance are diverse, the case raises questions as to the required follow-up of these patients and as to whether a low oxalate diet should be initiated.

[A case of Xanthinuria in a patient with marked hypouricemia]

Xanthinuria is a rare autosomal recessive disorder associated with a deficiency of xanthine oxidoreductase (XOR), which normally catalyzes the conversion of hypoxanthine to uric acid. The effects of this deficit are an elevated concentration of hypoxanthine and xanthine in the blood and urine, hypouricemia, and hypouricuria. The deficit in XOR can be isolated (type I xanthinuria) or associated with a deficit in aldehyde oxidase (type II xanthinuria) and sulfite oxidase (type III xanthinuria). While the first two variants have a benign course, are often asymptomatic (20%), and clinically indistinguishable, type III xanthinuria is a harmful form that leads to infant death due to neurological damage. The clinical symptoms (kidney stones, CKD, muscle and joint pain, peptic ulcer) are the result of the accumulation of xanthine, which is highly insoluble, in the body fluids. We describe a case of type I xanthinuria in a 52-year-old woman who presented with hypouricemia, hypouricuria and kidney stones. The diagnosis was based on purine catabolite levels in urine and serum measured by 3 nonroutine methods: high-pressure liquid chromatography, mass spectrometry, and magnetic resonance imaging. To identify the type of xanthinuria the allopurinol test was used. We believe that these tests will facilitate the diagnosis of xantinuria especially in asymptomatic patients without the need for a biopsy of the liver or intestines, which is useful only for scientific purposes.

Adenylosuccinate lyase deficiency in a Malaysian patient, with novel adenylosuccinate lyase gene mutations

Most cases of adenylosuccinate lyase (ADSL OMIM 103050) deficiency reported to date are confined to the various European ethnic groups. We report on the first Malaysian case of ADSL deficiency, which appears also to be the first reported Asian case. The case was diagnosed among a cohort of 450 patients with clinical features of psychomotor retardation, global developmental delay, seizures, microcephaly and/or autistic behaviour. The patient presented with frequent convulsions and severe myoclonic jerk within the first few days of life and severe psychomotor retardation. The high performance liquid chromatography (HPLC) profile of the urine revealed the characteristic biochemical markers of succinyladenosine (S-Ado) and succinyl-aminoimidazole carboximide riboside (SAICAr). The urinary S-Ado/SAICAr ratio was found to be 1.02 (type I ADSL deficiency). The patient was compound heterozygous for two novel mutations, c.445C > G (p.R149G) and c.774_778insG (p.A260GfsX24).

[Xanthinuria type I as the cause of nephrolithiasis in 17-years old girl]

Classic xanthinuria is a rare metabolic defect concerning the final reactions of purine catabolism. There are two types of the disorder: type I results from xanthine dehydrogenase (XDH) deficiency, while type II is characterized by lack of both XDH and aldehyde oxidase activity. Both types are clinically similar and are characterized by elevated xanthine concentration in body fluids that can lead to xanthine crystallisation. The most common manifestation of the disease is urolithiasis, but in most cases xanthinuria remains asymptomatic and the diagnosis is accidental. In the paper we report the first case study of xanthinuria in Poland in a child presenting with urolithiasis. 17-years old female patient was diagnosed because of recurrent urinary lithiasis and hypouricemia was detected during routine tests. Plasma and urine concentrations of oxypurines were measured by high-performance liquid chromatography (HPLC) and showed typical features of xanthinuria: hypouricemia, hypouricosuria, xanthinuria and elevated plasma xanthine. The allopurinol loading test demonstrated type I xanthinuria. The presented case report supports that first symptoms of xanthinuria can appear at any age and this disorder should be considered during diagnosing urolithiasis.

Xanthine urolithiasis

Hereditary xanthinuria type I, a defect of purine metabolism, results from a genetic deficiency of xanthine oxidase. It is an uncommon cause of stone formation in children. We report here two children with xanthine urolithiasis. The first patient was an 8-year-old boy who presented with repeated episodes of hematuria evaluated with excretory urography, which demonstrated radio-lucent pelvic stone in the right kidney, causing hydronephrosis. He had pyelolithotomy, and the extracted stone consisted of pure xanthine. Family study revealed an asymptomatic xanthinuria in younger brother. The second patient was a 5-year-old boy who had a 2-week history of abdominal pain and gross hematuria. Conventional excretory intravenous urography showed a non-functioning right kidney. Nephrectomy was performed, and histology revealed end-stage pyelonephritis. The calculi consisted of pure xanthine. In both patients, plasma and urinary concentrations of uric acid were low but xanthine and hypoxanthine concentrations were markedly elevated. Xanthine urolithiasis is usually a benign condition, easy to prevent or cure by appropriate alkalinization, forced hydration and restriction of dietary purines. However asymptomatic, and therefore undiagnosed, stones may invade the kidney and urinary tract, resulting in destruction of parenchyma, nephrectomy and renal failure.

Orotic aciduria and uridine monophosphate synthase: a reappraisal

Three subtypes of hereditary orotic aciduria are described in the literature, all related to deficiencies in uridine monophosphate synthase, the multifunctional enzyme that contains both orotate: pyrophosphoryl transferase and orotidine monophosphate decarboxylase activities. The type of enzyme defect present in the subtypes has been re-examined by steady-state modelling of the relative outputs of the three enzymic products, uridine monophosphate, urinary orotic acid and urinary orotidine. It is shown that the ratio of urinary outputs of orotidine to orotate provides a means of testing for particular forms of enzyme defect. It is confirmed that the type I defect is caused by loss of uridine monophosphate synthase activity. Cells and tissue of type I cases have a residual amount of activity that is qualitatively unchanged: the relative rates of the transferase and decarboxylase do not differ from those of wild-type enzyme. The single claimed case of type II, thought to be due to specific inactivation of orotidine monophosphate decarboxylase, is shown to have a product spectrum inconsistent with that claim. It is proposed that this type II form does not differ sufficiently to be accepted as separate from type I. The third subtype, hereditary orotic aciduria without megaloblastic anaemia, occurs in two cases. It has the product spectrum expected of a defect in orotidine monophosphate decarboxylase. This form is the only one that appears to have a qualitatively different uridine monophosphate synthase. The possibility that orotidine monophosphate may control flux through the pyrimidine biosynthesis pathway in hereditary orotic aciduria is discussed.

Severe encephalopathy with brain atrophy and hypomyelination due to adenylosuccinate lyase deficiency--MRI, clinical, biochemical and neuropathological findings of Polish patients

Adenylosuccinate lyase (ADSL) deficiency is an autosomal recessive disorder caused by mutation in the ADSL gene. The disease was identified in 1984 by Jaeken and van der Berghe as the first inborn defect of purine biosynthesis. Affected children revealed encephalopathy with epilepsy and marked psychomotor retardation. A neurological examination showed hypotonia, followed sometimes after years by spasticity. The diagnosis is based on detection in the urine and CSF succinyladenosine (S-Ado) and succinylaminoimidazole carboxamide ribotide (SAICAr). We present brain MR examinations of seven patients with ADSL deficiency in the correlation with their clinical findings. In all cases lack of myelination or of delayed myelination of cerebral white matter was seen. Additionally cerebral and cerebellar atrophy was observed. Neuropathological findings revealed damage of all cellular elements of brain tissue and are cause of observed MR changes. Hypo/dysmyelination seemed to be secondary to damage of oligodendroglia and axons of damaged neuronal cells.

D-ribose therapy in four Polish patients with adenylosuccinate lyase deficiency: absence of positive effect

Deficiency of adenylosuccinate lyase (ADSL) (OMIM 103050) is an autosomal recessive disorder of the purine de novo synthesis pathway and purine nucleotide cycle, diagnosed so far in approximately 50 patients. The clinical presentation is characterized by severe neurological involvement including hypotonia, seizures, developmental delay and autistic features. Epilepsy in ADSL deficiency is frequent and occurs in approximately two-thirds of patients, beginning either early in the neonatal period or after the first year of life. At present there is no treatment of proven clinical efficacy. Despite of the increasing number of ADSL-deficient patients reported, there are only a few communications of therapeutic considerations or efforts. Among them only two showed some beneficial effects in ADSL-deficient patients. D-ribose, a simple and relatively cheap therapy, has been associated with improvement of behaviour and progressive reduction of the seizure frequency in one 13-year-old patient with ADSL deficiency. In this study we have re-examined D-ribose treatment in four ADSL-deficient patients. Assessments consisted of biochemical markers and neurological outcome. The 12-month trial of D-ribose failed to show any clinical benefit in ADSL patients with both milder and severe phenotype. D-ribose administration was accompanied by neither reduction in seizure frequency nor growth enhancement. Additionally, patients with milder type II presented the first seizure after 4 and 8 months of the D-ribose treatment. Therefore, we could not confirm a positive effect of D-ribose as previously reported.

Lithiases urinaires récidivantes révélant une xanthinurie héréditaire

INTRODUCTION

Hereditary xanthinuria, due to a purine metabolism disorder, is a rare cause of urinary lithiasis in children.

CASE

We report the case of a child aged 3 and a half years, who presented recurrent urinary lithiasis that led to destruction of the right kidney. Infrared spectrophotometric analysis of the calculus concluded that it was composed of 100% xanthine. Laboratory tests showed hypouricemia and hypouricosuria with elevated urinary excretion of oxypurines. These findings led to a diagnosis of hereditary xanthinuria.

CONCLUSION

Early diagnosis of this rare disease is essential to avoid its complications. Metabolic causes must be sought in children with lithiasis.

Progressive multifocal leukoencephalopathy in purine nucleoside phosphorylase deficiency

Progressive multifocal leukoencephalopathy is a demyelinating disease caused by JC virus, an opportunistic infection of the central nervous system. Although the majority of cases are infected with the human immunodeficiency virus (HIV), other immunocompromised patients are also at risk. Purine nucleoside phosphorylase is an enzyme in the purine salvage pathway that reversibly converts inosine to hypoxanthine and guanosine to guanine. Purine nucleoside phosphorylase deficiency is a combined immunodeficiency with a profound cellular defect. Neurologic abnormalities are salient features of this syndrome. We describe for the first time a patient with this rare disorder presented with progressive multifocal leukoencephalopathy.

Xanthinuria type I: a rare cause of urolithiasis

Xanthinuria type I is a rare disorder of purine metabolism caused by xanthine oxidoreductase or dehydrogenase (XDH) deficiency. We report a family with two affected children out of 335 pediatric stone patients studied since 1991 in Armenia. The propositus, a 13-month-old boy, presented with abdominal pain and urinary retention followed by stone passage (0.9x0.6 cm). Infrared spectroscopy in Yerevan revealed a pure xanthine stone. Family examination in the parents and brother was normal, but the propositus and his 8-year-old asymptomatic sister had hypouricemia, hypouricosuria, and high urinary excretion of hypoxanthine and xanthine. Ultrasonography in the index patient showed bilateral stones requiring pyelolithotomy. High fluid intake and purine restriction did not prevent further stone passages. The affected asymptomatic sister had a small pelvic stone (4 mm). Mutation analysis revealed a heterozygous novel base pair substitution in exon 25 of the XDH gene (c.2810C>T), resulting in an amino acid substitution (p.Thr910Met). The second mutation could not be detected. Despite this, the heterozygous mutation, the chemical findings, and the positive allopurinol test altogether prove xanthinuria type I, which may present wide clinical intrafamilial variation. Diagnosis is suspected usually from low serum uric acid. No specific therapy is available.

Lethal fetal and early neonatal presentation of adenylosuccinate lyase deficiency: observation of 6 patients in 4 families

OBJECTIVE

To characterize a new lethal fetal and early postnatal variant of adenylosuccinate lyase (ADSL) deficiency.

STUDY DESIGN

This was a retrospective analysis of 6 patients with very early presentation of ADSL deficiency.

RESULTS

Most of the 6 patients had impaired intrauterine growth, microcephaly, fetal hypokinesia, and a lack of fetal heart rate variability. Postnatally, they shared severe muscular hypotonia necessitating mechanical ventilation, intractable seizures, and early death. All 6 patients had biochemical evidence of severe (type 1) disease and low residual ADSL activities. All were compound heterozygous for mutations that, based on expression studies, have a pronounced effect on ADSL activity and/or stability.

CONCLUSIONS

ADSL deficiency may present with prenatal growth restriction, fetal and neonatal hypokinesia, and rapidly fatal neonatal encephalopathy. This clinical presentation is associated with genotypes resulting in very low residual enzyme activity.

Clinical findings and a therapeutic trial in the first patient with beta-ureidopropionase deficiency

The clinical, neurophysiological and neuroradiological work-up as well as the results of a specific treatment trial are presented of the first patient diagnosed with beta-ureidopropionase deficiency (E.C. 3.5.1.6, McKusick 606673). The patient presented with an early-onset dystonic movement disorder, severe developmental delay with marked impairment of visual responsiveness in combination with severely delayed myelination in magnetic resonance imaging studies. In addition, there were partial optic atrophy, pigmentary retinopathy and mild cerebellar hypoplasia. The enzyme defect was expected to lead to intracerebral deficiency of beta-alanine which seems to be a neuromodulator at inhibitory synapses. Therefore, a therapeutic trial with supplementation of beta-alanine was undertaken over 1.5 years with no convincing clinical improvement.

β-Ureidopropionase deficiency: an inborn error of pyrimidine degradation associated with neurological abnormalities

beta-Ureidopropionase deficiency is an inborn error of the pyrimidine degradation pathway, affecting the cleavage of N-carbamyl-beta-alanine and N-carbamyl-beta-aminoisobutyric acid. In this study, we report the elucidation of the genetic basis underlying a beta-ureidopropionase deficiency in four patients presenting with neurological abnormalities and strongly elevated levels of N-carbamyl-beta-alanine and N-carbamyl-beta-aminoisobutyric acid in plasma, cerebrospinal fluid and urine. No beta-ureidopropionase activity could be detected in a liver biopsy obtained from one of the patients, which reflected the complete absence of the beta-ureidopropionase protein. Analysis of the beta-ureidopropionase gene (UPB1) of these patients revealed the presence of two splice-site mutations (IVS1-2A>G and IVS8-1G>A) and one missense mutation (A85E). Heterologous expression of the mutant enzyme in Escherichia coli showed that the A85E mutation resulted in a mutant beta-ureidopropionase enzyme without residual activity. Our results demonstrate that the N-carbamyl-beta-amino aciduria in these patients is due to a deficiency of beta-ureidopropionase, which is caused by mutations in the UPB1 gene. Furthermore, an altered homeostasis of beta-aminoisobutyric acid and/or increased oxidative stress might contribute to some of the clinical abnormalities encountered in patients with a beta-ureidopropionase deficiency. An analysis of the presence of the two splice site mutations and the missense mutation in 95 controls identified one individual who proved to be heterozygous for the IVS8-1G>A mutation. Thus, a beta-ureidopropionase deficiency might not be as rare as is generally considered.

Dihydropyrimidine dehydrogenase deficiency and acute neurological presentation

Dihydropyrimidine dehydrogenase (DPD) deficiency has been linked to 5-fluorouracil toxicity, but patients may present a wide clinical spectrum. We describe a 1-year-old Tunisian girl with a dramatic onset of neurological symptoms suggesting the possible triggering role of environmental factors.

[Urine fibrinolytic activity as an indicator of kidney damage in uric acid metabolic imbalance]

AIM

To determine functional fibrinolytic activity of the urine in patients with different forms of purine metabolism disorder.

MATERIAL AND METHODS

Uricemia, 24-h uricosuria, serum creatinine, GFR, maximal urinary specific gravity, urokinase activity in the urine, total fibrinolytic activity of the urine (TFAU), activity of plasminogen activator inhibitor (PAI) in blood were studied in 33 patients with genetically determined purine metabolism disorders.

RESULTS

Patients with purine metabolism disorders vs controls had decreased TFAU and urokinase activity. There was no significant difference between the study and control groups in the levels of PAI in blood. No statistically significant difference was found between the patients with hyperuricemia and patients with hyperuricosuria in the levels of TFAU and urokinase activity, while the group with hyperuricemia was characterized by a decreased maximal specific urinary gravity.

CONCLUSION

A decrease in TFAU and urokinase activity in patients with purine metabolism disorder was observed in the isolated hyperuricosuric stage of urite renal damage.

Analysis of purines in urinary calculi by high-performance liquid chromatography

A high-pressure liquid chromatography method has been developed for the analysis in urinary calculi of six purines: uric acid, 2, 8-dihydroxyadenine, xanthine, hypoxanthine, allopurinol, and oxypurinol. Separation was conducted isocratically on a reversed-phase column, using 50 mM phosphate buffer (pH 5.5) / methanol (97/3, v/v) as mobile phase. Limits of detection, depending on compound, ranged from 7 to 28 microg/g stone weight. Hitherto, no reports have appeared on other purines present with uric acid in stones, due to lack of a sensitive and specific analytical method. We have now found that all calculi with more than 4% uric acid also contained 1-methyluric and 7-methyluric acids and trace amounts of hypoxanthine, xanthine, and 2,8-dihydroxyadenine. Accurate identification and quantitation of purines in urinary calculi are important for the diagnosis of rare metabolic diseases leading to urolithiasis (xanthinuria, dihydroxyadeninuria), as well as for prevention of iatrogenic complications during treatment with allopurinol of uric acid urolithiasis. The method may be used for reference purposes in clinical laboratories and for research on the pathogenesis of urolithiasis in disorders of purine metabolism.

[Phosphoribosyltransferase (APRT) deficiency--molecular and clinical aspects of dihydroxyadeninuria]

The lack of purine salvage enzyme, adenine phosphoribosyltransferase (APRT), is a rare genetic defect that leads to excessive excretion of 2,8-dihydroxyadenine in urine. Due to its low solubility and nephrotoxicity, the defect may result in urolithiasis and renal failure. This review article describes genetic, biochemical and biophysical basis of the disease called dihydroxyadeninuria, as well as clinical problems of diagnosis and treatment.

Adenylosuccinase deficiency with neonatal onset severe epileptic seizures and sudden death

We report a male infant with adenylosuccinase deficiency who developed epileptic seizures on the second day of life. Growth was normal and seizures were well controlled with anti-epileptic drugs. Despite axial hypotonia associated with peripheral hypertonicity he presented some development until seven months of age, when he developed high fever and died within a few hours. Although clinical heterogeneity in this disorder of purine synthesis and interconversion is well-known, in 14 out of 17 cases who experienced epilepsy seizures started after the first year of life. The early presentation in our index patient followed by his sudden death at the age of 7 months has not been described before. A search for disorders of purine metabolism should be included in the screening programme for every child with severe neonatal convulsions.

Partial adenine phosphoribosyltransferase deficiency detected by ureterolithiasis

A 30-year-old woman was admitted to our hospital because of recurrent ureterolithiasis. She was suspected of having adenine phosphoribosyltransferase (APRT) deficiency based on the presence of 2,8-dihydroxyadenine (DHA) crystals in her urinary sediment, infrared spectrophotometric analysis of the excreted stone, and then the definitive diagnosis by gene analysis. A pedigree study indicated only a slight possibility of this disease in the family. From these results, we consider that urinary sediment and stone analysis should be used for screening while gene analysis should be employed for definitive diagnosis of APRT deficiency, so that the complications of this condition can be prevented.

Dihydropyrimidine dehydrogenase (DPD) deficiency: identification and expression of missense mutations C29R, R886H and R235W

Dihydropyrimidine dehydrogenase (DPD) deficiency (McKusick 274270) is an autosomal recessive disease characterized by thymine-uraciluria in homozygous-deficient patients and associated with a variable clinical phenotype. Cancer patients with this defect should not be treated with the usual dose of 5-fluorouracil because of the expected lethal toxicity. In addition, heterozygosity for mutations in the DPD gene increases the risk of toxicity in cancer patients treated with this drug. Sequence analysis in a patient with complete DPD deficiency, previously shown to be heterozygous for the delta C1897 frame-shift mutation, revealed the presence of a novel missense mutation, R235W. Expression of this novel mutation and previously identified missense mutations C29R and R886H in Escherichia coli showed that both C29R and R235W lead to a mutant DPD protein without significant residual enzymatic activity. The R886H mutation, however, resulted in about 25% residual enzymatic activity and is unlikely to be responsible for the DPD-deficient phenotype. We show that the E. coli expression system is a valuable tool for examining DPD enzymatic variants. In addition, two new patients who were both heterozygous for the C29R mutation and the common splice donor site mutation were identified. Only one of these patients showed convulsive disorders during childhood, whereas the other showed no clinical phenotype, further illustrating the lack of correlation between genotype and phenotype in DPD deficiency.

Dihydropyrimidinase deficiency, a progressive neurological disorder?

A case of a child presenting with congenital abnormalities at birth is reported. The early development remained severely retarded and acquired skills minimally. The head circumference centile decreased. Magnetic resonance imaging showed progressive neuronal atrophy and secondary delay in myelination. Dihydropyrimidine concentrations in body fluids were quantitated by NMR spectroscopy. Enzymatic assay in the liver biopsy revealed total deficiency of dihydropyrimidinase (DHP) (5,6-dihydropyrimidine amidohydrolase; EC 3.5.2.2). As such, the patient is the first with enzymatically proven DHP deficiency. Thus far dihydropyrimidinuria has been reported in three other patients with a variety of neurological abnormalities. A relation of the enzyme deficiency with the neurodegenerative clinical course in our patient is suggested.

Ureteral xanthine calculus and aberrant umbilical artery causing ureteral obstruction

A 30-month-old girl presented with gastrointestinal symptoms and a febrile urinary tract infection. Sonographic and radiographic imaging demonstrated left hydronephrosis due to a radiolucent ureteral stone. Surgical exploration identified an aberrant, patent left umbilical artery causing ureteral obstruction. Stone and urine analyses revealed hereditary xanthinuria that had not previously been recognized in this child and her family.

Correction of purine nucleoside phosphorylase deficiency by transplantation of allogeneic bone marrow from a sibling

Deficiency of the purine salvage pathway enzyme purine nucleoside phosphorylase causes a combined immunodeficiency and neurologic abnormalities and is usually fatal in childhood. We report the first successful transplantation of bone marrow from a sibling with identical class II human leukocyte antigens in this condition, demonstrating correction of both lymphocyte metabolic and functional abnormalities.

[Urolithiasis in 2,8-dihydroxyadeninuria: presentation of 3 additional cases]

To the now 17 case reports in caucasian patients of an urolithiasis in a rare purine metabolism disorder 2,8-dihydroxyadeninuria due to missing activity of adenine phosphoribosyltransferase 3 further cases are presented. Firstly, a monozygotic twin pair is afflicted (13-year-old boys). All calculi be composed of pure 2,8-DHA, except a mixed calculus in a 38-year-old man containing of 80% 2,8-DHA and 20% calcium oxalate. The actual literature is reviewed.

A new case of dihydropyrimidine dehydrogenase deficiency

We present the clinical and biochemical features of a boy with dihydropyrimidine dehydrogenase deficiency, which seem to underline a disease entity of developmental retardation, epilepsy and muscular hypertonia.

Purine enzyme defects as a cause of acute renal failure in childhood

Acute renal failure (ARF) is not listed as a usual form of presentation in hypoxanthine-guanine phosphoribosyltransferase deficiency, despite the gross uric acid overproduction in the defect. We found that a third of such patients may present in ARF when the urinary uric acid/creatinine ratio may be normal, not raised, and the defect may be suspected from the disproportionate increase in plasma uric acid. This is important in view of the potential confusion of uric acid with 2,8-dihydroxyadenine, the even more insoluble purine excreted in the other salvage enzyme disorder, adenine phosphoribosyltransferase deficiency. In that disorder, presentation in ARF is well recognized, the uric acid/creatinine ratio is also normal, but plasma urate is not raised. Our combined experience in these two disorders underlines the importance of early recognition and treatment with carefully adjusted doses of allopurinol, which may reverse or postpone renal failure.

Hereditary xanthinuria in 2 Pakistani sisters: asymptomatic in one with beta-thalassemia but causing xanthine stone, obstructive uropathy and hypertension in the other

We describe a 3-year-old Pakistani girl who presented with recurrent urinary infections. She had a nonfunctioning hydronephrotic right kidney and hypertension. At operation a calculus was impacted in the right ureter with dilatation of the pelviocaliceal system. Nephrectomy was performed. Histology revealed end stage pyelonephritis. The calculus consisted of pure xanthine. Further investigations demonstrated low serum uric acid and absent urinary uric acid with increased excretion of xanthine. Eight months after nephrectomy blood pressure had decreased to normal. Her 5-year-old sister, who has beta-thalassemia, also has a low serum uric acid concentration and xanthinuria. The treatment of choice is to increase fluid intake so that the urine xanthine concentration remains below the level at which xanthine crystallizes. This may require adjustment of the urine pH.

2,8-Dihydroxyadenine urolithiasis: report of an adult case in the United States

2,8-Dihydroxyadeninuria is a rare purine metabolic disorder that has been reported to have caused urolithiasis in 14 cases, mostly children. Excretion of the hydroxylated metabolites of adenine results from a deficiency of adenine phosphoribosyltransferase. The insoluble calculi have a similar chemical structure to uric acid and frequently are misdiagnosed as uric acid calculi. Management differs from that of uric acid urolithiasis. We report on an adult with 2,8-dihydroxyadenine urolithiasis in the United States.

Uridine monophosphate kinase and susceptibility to invasive Haemophilus influenzae type B disease

A polymorphic genetic variant of the pyrimidine pathway enzyme, uridine monophosphate kinase-3 (UMPK-3), was positively associated with invasive Hib disease. All UMPK 3-3 homozygotes in this study were Hib cases, and we found that in cases and controls, there was no difference between UMPK phenotype and serum levels of total Hib antibody as measured by radioimmunoassay. This suggests that UMPK-3 may play a role in mediating the non-humoral immunity to Hib. However, unlike other enzyme variants in the nucleoside synthesis pathways which result in syndromes of severe immunodeficiency, this gene appears to confer a more subtle disease susceptibility. Thus, the UMPK-3 allele, although rare in Caucasians, is associated with an increased risk of invasive Hib infection in Alaskan Eskimos.