Deletion of Mocos Induces Xanthinuria with Obstructive Nephropathy and Major Metabolic Disorders in Mice.

Background: Xanthinuria type II is a rare autosomal purine disorder. This recessive defect of purine metabolism remains an under-recognized disorder. Methods: Mice with targeted disruption of the molybdenum cofactor sulfurase (Mocos) gene were generated to enable an integrated understanding of purine disorders and evaluate pathophysiologic functions of this gene which is found in a large number of pathways and is known to be associated with autism. Results: Mocos-deficient mice die with 4 weeks of age due to renal failure of distinct obstructive nephropathy with xanthinuria, xanthine deposits, cystic tubular dilation, Tamm-Horsfall (uromodulin) protein (THP) deposits, tubular cell necrosis with neutrophils, and occasionally hydronephrosis with urolithiasis. Obstructive nephropathy is associated with moderate interstitial inflammatory and fibrotic responses, anemia, reduced detoxification systems, and important alterations of the metabolism of purines, amino acids, and phospholipids. Conversely, heterozygous mice expressing reduced MOCOS protein are healthy with no apparent pathology. Conclusions: Mocos-deficient mice develop a lethal obstructive nephropathy associated with profound metabolic changes. Studying MOCOS functions may provide important clues about the underlying pathogenesis of xanthinuria and other diseases requiring early diagnosis.

An unusual presentation of purine nucleoside phosphorylase deficiency mimicking systemic juvenile idiopathic arthritis complicated by macrophage activation syndrome.

BACKGROUND: Systemic juvenile idiopathic arthritis (sJIA) is an inflammatory condition that presents with fever, rash and arthritis. At onset systemic features are predominant and the diagnosis may be a challenge. Secondary hemophagocytic lymphohistiocytosis (sHLH) forms may be associated with different disorders, including rheumatic diseases, and this form is called macrophage activation syndrome (MAS). CXCL9 levels, a chemokine induced by IFNγ, are significantly elevated in patients with sHLH or MAS and are correlated with laboratory features of disease activity. High levels of IL-18 have been reported in patients with MAS during sJIA, as well as in some patients with sHLH and IL-18 is indeed known to induce IFNγ production. FINDINGS: We report a patient with a clinical presentation highly suggestive for systemic juvenile idiopathic arthritis (sJIA) onset complicated by MAS, and was later diagnosed with purine nucleoside phosphorylase (PNP)-deficiency with HLH. Some unusual features appeared when HLH was controlled and further investigations provided the correct diagnosis. Serum CXCL9 and IL-18 levels were found markedly elevated at disease onset, during the active phase of MAS and decreased progressively during the course. CONCLUSION: The reported case underlines the potential difficulties in discriminating sJIA from other causes of systemic inflammation. Furthermore, this supports the notion that especially in young children with a sJIA-like disease other mimicking conditions should be actively sought for. CXCL9 and IL-18 levels suggested that patients with PNP-deficiency may have a subclinical activation of the IFNγ pathway and indeed they are predisposed to develop sHLH.

A case of dihydropyrimidinase deficiency incidentally detected by urine metabolome analysis.

Dihydropyrimidinase deficiency is a rare autosomal recessive disease affecting the second step of pyrimidine degradation. It is caused by mutations in the DPYS gene. Only approximately 30 cases have been reported to date, with a phenotypical variability ranging from asymptomatic to severe neurological illness. We report a case of dihydropyrimidinase deficiency incidentally detected by urine metabolome analysis. Gas chromatography-mass spectrometry-based urine metabolomics demonstrated significant elevations of dihydrouracil and dihydrothymine, which were subsequently confirmed by a quantitative analysis using liquid chromatography-tandem mass spectrometry. Genetic testing of the DPYS gene revealed two mutations: a novel mutation (c.175G > T) and a previously reported mutation (c.1469G > A). Dihydropyrimidinase deficiency is probably underdiagnosed, considering its wide phenotypical variability, nonspecific neurological presentations, and an estimated prevalence of 2/20,000. As severe 5-fluorouracil-associated toxicity has been reported in patients and carriers of congenital pyrimidine metabolic disorders, urinary pyrimidine analysis should be considered for those who will undergo 5-fluorouracil treatment.

Clinical manifestations and molecular aspects of phosphoribosylpyrophosphate synthetase superactivity in females.

Objectives: Phosphoribosylpyrophosphate synthetase (PRPS1) superactivity is an X-linked disorder characterized by urate overproduction Online Mendelian Inheritance in Man (OMIM) gene reference 300661. This condition is thought to rarely affect women, and when it does, the clinical presentation is mild. We describe a 16-year-old African American female who developed progressive tophi, nephrolithiasis and acute kidney failure due to urate overproduction. Family history included a mother with tophaceous gout who developed end-stage kidney disease due to nephrolithiasis and an affected sister with polyarticular gout. The main aim of this study was to describe the clinical manifestations of PRPS1 superactivity in women. Methods: Whole exome sequencing was performed in affected females and their fathers. Results: Mutational analysis revealed a new c.520 G > A (p.G174R) mutation in the PRPS1 gene. The mutation resulted in decreased PRPS1 inhibition by ADP. Conclusion: Clinical findings in previously reported females with PRPS1 superactivity showed a high clinical penetrance of this disorder with a mean serum urate level of 8.5 (4.1) mg/dl [506 (247) µmol/l] and a high prevalence of gout. These findings indicate that all women in families with PRPS1 superactivity should be genetically screened for a mutation (for clinical management and genetic counselling). In addition, women with tophaceous gout, gout presenting in childhood, or a strong family history of severe gout should be considered for PRPS1 mutational analysis.

Peripartum anaesthetic management of a patient with Brugada syndrome and myoadenylate deaminase deficiency.

Brugada syndrome is a rare electrophysiological cardiac disease which can result in serious arrhythmias and sudden cardiac death. Peripartum management is centred around avoiding arrhythmogenic drugs, including high doses of sodium channel blocking drugs such as bupivacaine. Myoadenylate deaminase deficiency, also known as adenosine monophosphate deaminase deficiency, is the commonest cause of myopathy in Caucasians. There is evidence that myoadenylate deaminase deficiency can predispose patients to developing malignant hyperthermia when exposed to specific anaesthetic agents. We present a case of a pregnant patient with both Brugada syndrome and myoadenylate deaminase deficiency, in which analgesic and general anaesthetic options for each condition presented potentially conflicting dilemmas for the delivery of intrapartum care.

Myoadenylate deaminase deficiency: a frequent cause of muscle pain A case detected by exercise testing.

Myoadenylate deaminase deficit (MAD, MIM#615511) is the most common cause of metabolic myopathies with an estimated prevalence of 1-2% in the general population. We report the case of a 39-year-old man suffering from severe skeletal muscle pain that had developed gradually for 4 years. A moderate increase in creatine kinase (CK) was the only biological sign observed. This study takes a closer look at a common but poorly known pathology and highlights the interest of the dynamic metabolic investigations carried out during exercise stress test with a cycle ergometer. Our non-invasive clinical and biological examination, at the interface between physiology and biology, disclosed the total absence of a physiological increase in plasma ammonia evocative of MAD. However, MAD was later confirmed by histochemistry and molecular studies, which revealed the presence of the recurrent homozygous pathogenic variant affecting the adenosine monophosphate deaminase 1 gene (AMPD1) in most patients with MAD.

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.

Azathioprine Therapy in a Pediatric TPMT-Deficient Patient-Still an Option.

We describe the case of a pediatric patient on azathioprine therapy with previously undiagnosed homozygote thiopurine S-methyltransferase (TPMT) deficiency, resulting in myelotoxic thiopurine metabolite levels. The patient was successfully treated with a very low azathioprine dose of 50 mg once a week (4% of standard dose), guided by frequent thiopurine metabolite measurement and a close clinical surveillance. We demonstrate that azathioprine therapy still might be an effective and safe therapeutic option in pediatric thiopurine S-methyltransferase-deficient IBD patients.

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.

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.

Expanding the phenotype of PRPS1 syndromes in females: neuropathy, hearing loss and retinopathy.

BACKGROUND: Phosphoribosyl pyrophosphate synthetase (PRS) I deficiency is a rare medical condition caused by missense mutations in PRPS1 that lead to three different phenotypes: Arts Syndrome (MIM 301835), X-linked Charcot-Marie-Tooth (CMTX5, MIM 311070) or X-linked non-syndromic sensorineural deafness (DFN2, MIM 304500). All three are X-linked recessively inherited and males affected display variable degree of central and peripheral neuropathy. We applied whole exome sequencing to a three-generation family with optic atrophy followed by retinitis pigmentosa (RP) in all three cases, and ataxia, progressive peripheral neuropathy and hearing loss with variable presentation. METHODS: Whole exome sequencing was performed in two affecteds and one unaffected member of the family. Sanger sequencing was used to validate and segregate the 12 candidate mutations in the family and to confirm the absence of the novel variant in PRPS1 in 191 controls. The pathogenic role of the novel mutation in PRPS1 was assessed in silico and confirmed by enzymatic determination of PRS activity, mRNA expression and sequencing, and X-chromosome inactivation. RESULTS: A novel missense mutation was identified in PRPS1 in the affected females. Age of onset, presentation and severity of the phenotype are highly variable in the family: both the proband and her mother have neurological and ophthalmological symptoms, whereas the phenotype of the affected sister is milder and currently confined to the eye. Moreover, only the proband displayed a complete lack of expression of the wild type allele in leukocytes that seems to correlate with the degree of PRS deficiency and the severity of the phenotype. Interestingly, optic atrophy and RP are the only common manifestations to all three females and the only phenotype correlating with the degree of enzyme deficiency. CONCLUSIONS: These results are in line with recent evidence of the existence of intermediate phenotypes in PRS-I deficiency syndromes and demonstrate that females can exhibit a disease phenotype as severe and complex as their male counterparts.

Fuzzy optimization for detecting enzyme targets of human uric acid metabolism.

MOTIVATION: Mathematical modeling and optimization have been used for detecting enzyme targets in human metabolic disorders. Such optimal drug design methods are generally differentiated as two stages, identification and decision-making, to find optimal targets. We developed a unified method named fuzzy equal metabolic adjustment to formulate an optimal enzyme target design problem for drug discovery. The optimization framework combines the identification of enzyme targets and a decision-making strategy simultaneously. The objectives of this algorithm include evaluations of the therapeutic effect of target enzymes, the adverse effects of drugs and the minimum effective dose (MED). RESULTS: An existing generalized mass action system model of human uric acid (UA) metabolism was used to formulate the fuzzy optimization method for detecting two types of enzymopathies: hyperuricemia caused by phosphoribosylpyrophosphate synthetase (PRPPS) overactivity and Lesch-Nyhan syndrome. The fuzzy objectives were set so that the concentrations of the metabolites were as close as possible to the healthy levels. The target design included a diet control of ribose-5-phospahate (R5P). The diet control of R5P served as an extra remedy to reduce phosphate uptake entering the purine metabolic pathway, so that we could obtain a more satisfactory treatment than obtained for those without a diet control. Moreover, enhancing UA excretion resulted in an effective treatment of hyperuricemia caused by PRPPS overactivity. This result correlates with using probenecid and benbromazone, which are uricosuric agents present in current clinical medications. By contrast, the Lesch-Nyhan syndrome required at least three enzyme targets to cure hyperuricemia.

[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.

Magnetic resonance imaging of the brain in adenylosuccinate lyase deficiency: a report of seven cases and a review of the literature.

Adenylosuccinate lyase (ADSL) deficiency is a rare autosomal recessive disorder of purine metabolism. Patients may present with a wide range of neurological symptoms. Head imaging abnormalities have been reported only rarely in the scientific literature and include atrophy of the cerebral cortex, corpus callosum, cerebellar vermis, lack of myelination, delayed myelination, anomalies of the white matter, and lissencephaly. The pathogenesis of abnormalities remains unknown. To further the understanding of the spectrum of brain abnormalities associated with ADSL deficiency, we examined the magnetic resonance findings in seven Polish patients with different clinical phenotypes and genotypes. Head MRI showed impaired white matter myelination with various degrees of global supra- and infratentorial white matter loss including widening of the lateral ventricles, enlargement of the subarachnoid spaces, atrophy of the cerebrum, hypoplasia of the cerebellar hemispheres and enlargement of the cisterna magna, and white matter abnormal hyperintense signal on T(2)-weighted sequences. We recommend performing a detailed analysis of urine and plasma purine metabolites in patients who have neurological findings, including developmental delay, microcephaly, autistic features, neonatal encephalopathy, and seizures especially if MRI findings such as delayed or lack of myelination, white matter abnormal signal, and atrophy of the cerebrum and/or cerebellum are also present. Greater awareness of adenylosuccinate lyase deficiency among general pediatricians, neonatologists, pediatric neurologists, and also radiologists is the key to identifying the disorder at an early stage.

Neurologic presentation, diagnostics, and therapeutic insights in a severe case of adenylosuccinate lyase deficiency.

Epilepsy in adenylosuccinate lyase deficiency may be difficult to treat, and there is no standardized therapy. The authors describe a case of severe adenylosuccinate lyase deficiency resulting from a heterozygous mutation of the ADSL gene (p.D215H/p.I351T). The patient presented with tonic-clonic seizures, opisthotonus, tremor, and myoclonus in the 4th day of life. The seizures were refractory on various combinations of antiepileptic treatment. A ketogenic diet was introduced at the age of 2 resulting in a seizure-free period. The patient, however, developed a metabolic hyperchloremic acidosis with Fanconi syndrome, which disappeared a month after cessation of the diet at the age of 5. Since the withdrawal of the ketogenic diet, seizures have returned to a frequency of several times a day. In conclusion, a ketogenic diet could be considered a valid therapeutic option in patients with intractable seizures in a course of adenylosuccinate lyase deficiency; however, it requires a formal study.

[A case of Xanthinuria in a patient with marked hypouricemia]. / Un caso di xantinuria in una paziente con marcata ipouricemia.

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.

Limitations of extensive TPMT genotyping in the management of azathioprine-induced myelosuppression in IBD patients.

BACKGROUND AND AIMS: TPMT deficiency is associated with azathioprine (AZA)-induced myelosuppression (MS). However, in one previous study, only about » of MS episodes in Crohn's Disease patients under AZA can be attributed to TPMT deficiency. Recently, new TPMT mutations have been described and our aim is to investigate their clinical relevance before and after a first MS episode on thiopurine therapy. METHODS: Clinical data from 61 IBD patients having developed MS during AZA therapy were collected. Sequencing analysis was carried out on TPMT cDNA for the presence of all currently known mutations. RESULTS: Only TPMT *2, *3A and *3C mutations were found in this cohort. TPMT mutations were observed in 15 out of 61 patients (25%). Four out of 15 were homozygous for a TPMT mutation (low methylator, LM genotype) and 11 were heterozygous (intermediate methylator, IM genotype). Median delays of MS onset were 2, 2.75 and 6months in the LM, IM and HM (high methylator, wild type TPMT) groups, respectively. After the first MS episode, 36 patients resumed thiopurine treatment of which 13 experienced a second MS episode. This second episode was also rarely associated with TPMT mutations. CONCLUSIONS: One quarter of MS episodes during AZA were associated with TPMT deficient genotype. After a first leucopenia episode, thiopurine therapy may be resumed in a majority of patients independently of their TPMT genotype.