Succinylaminoimidazole Carboxamide Research Articles

Identification of pathognomonic purine synthesis biomarkers by metabolomic profiling of adolescents with obesity and type 2 diabetes

The incidence of type 2 diabetes is increasing more rapidly in adolescents than in any other age group. We identified and compared metabolite signatures in obese children with type 2 diabetes (T2D), obese children without diabetes (OB), and healthy, age- and gender-matched normal weight controls (NW) by measuring 273 analytes in fasting plasma and 24-hour urine samples from 90 subjects by targeted LC-MS/MS. Diabetic subjects were within 2 years of diagnosis in an attempt to capture early-stage disease prior to declining renal function. We found 22 urine metabolites that were uniquely associated with T2D when compared to OB and NW groups. The metabolites most significantly elevated in T2D youth included members of the betaine pathway, nucleic acid metabolism, and branched-chain amino acids (BCAAs) and their catabolites. Notably, the metabolite pattern in OB and T2D groups differed between urine and plasma, suggesting that urinary BCAAs and their intermediates behaved as a more specific biomarker for T2D, while plasma BCAAs associated with the obese, insulin resistant state independent of diabetes status. Correlative analysis of metabolites in the T2D signature indicated that betaine metabolites, BCAAs, and aromatic amino acids were associated with hyperglycemia, but BCAA acylglycine derivatives and nucleic acid metabolites were linked to insulin resistance. Of major interest, we found that urine levels of succinylaminoimidazole carboxamide riboside (SAICA-riboside) were increased in diabetic youth, identifying urine SAICA-riboside as a potential biomarker for T2D.

Identification of pathognomonic purine synthesis biomarkers by metabolomic profiling of adolescents with obesity and type 2 diabetes.

The incidence of type 2 diabetes is increasing more rapidly in adolescents than in any other age group. We identified and compared metabolite signatures in obese children with type 2 diabetes (T2D), obese children without diabetes (OB), and healthy, age- and gender-matched normal weight controls (NW) by measuring 273 analytes in fasting plasma and 24-hour urine samples from 90 subjects by targeted LC-MS/MS. Diabetic subjects were within 2 years of diagnosis in an attempt to capture early-stage disease prior to declining renal function. We found 22 urine metabolites that were uniquely associated with T2D when compared to OB and NW groups. The metabolites most significantly elevated in T2D youth included members of the betaine pathway, nucleic acid metabolism, and branched-chain amino acids (BCAAs) and their catabolites. Notably, the metabolite pattern in OB and T2D groups differed between urine and plasma, suggesting that urinary BCAAs and their intermediates behaved as a more specific biomarker for T2D, while plasma BCAAs associated with the obese, insulin resistant state independent of diabetes status. Correlative analysis of metabolites in the T2D signature indicated that betaine metabolites, BCAAs, and aromatic amino acids were associated with hyperglycemia, but BCAA acylglycine derivatives and nucleic acid metabolites were linked to insulin resistance. Of major interest, we found that urine levels of succinylaminoimidazole carboxamide riboside (SAICA-riboside) were increased in diabetic youth, identifying urine SAICA-riboside as a potential biomarker for T2D.

A mild form of adenylosuccinate lyase deficiency in absence of typical brain MRI features diagnosed by whole exome sequencing

BackgroundAdenylosuccinate lyase (ADSL) deficiency is a defect of purine metabolism affecting purinosome assembly and reducing metabolite fluxes through purine de novo synthesis and purine nucleotide recycling pathways. The disorder shows a wide spectrum of symptoms from slowly to rapidly progressing forms. The most severe form is characterized by neonatal encephalopathy, absence of spontaneous movement, respiratory failure, intractable seizures, and early death within the first weeks of life. More commonly, ADSL presents purely neurologic clinical picture characterized by severe psychomotor retardation, microcephaly, early onset of seizures, and autistic features (type I) or a more slowly progressing form with later onset, and major features including slight to moderate psychomotor retardation, and transient contact disturbances (type II). Diagnostic markers are the presence of succinylaminoimidazole carboxamide riboside (SAICAr) and succinyladenosine (SAdo) in extracellular fluids. ADSL is a rare disorder, although its prevalence remains unknown. Of note, the wide range of essentially nonspecific manifestations and lack of awareness of the condition often prevent diagnosis.Case presentationWe present here the case of particularly mild, late onset ADSL that has been unsuccessfully investigated until whole exome sequencing (WES) was performed.ConclusionsBesides emphasizing the valuable diagnostic value of WES, this report provides new data further documenting the relatively wide clinical manifestation of ADSL.

Elevation of Fumarate Levels Compromise Redox Control and Viability in Mycobacterium tuberculosis

In this issue of Cell Chemical Biology, Ruecker etal. (2017) show that fumarase depletion in Mycobacterium tuberculosis leads to fumarate, a TCA cycle intermediate, accumulation, causing succination of a range of thiol-containing metabolites and proteins. Fumarate is bactericidal to the pathogen, and its accumulation may enhance the bactericidal effector mechanisms of other TCA cycle intermediates that accumulate due to activation of infected macrophages.

Screening for adenylosuccinate lyase deficiency using tandem mass spectrometry analysis of succinylpurines in neonatal dried blood spots

ObjectivesStable isotope dilution coupled with liquid chromatography–tandem mass spectrometry (LC–MS/MS) is the sensitive method for screening for various inherited metabolic disorders using dried blood spots (DBSs). We present a method for LC–MS/MS determination of succinyladenosine (SAdo) and succinylaminoimidazole carboxamide riboside (SAICAr), biomarkers for adenylosuccinate lyase deficiency (dADSL), in DBS. Design and methodsSAICAr and SAdo were separated on a Symmetry-C18 column and detected using positive electrospray ionisation in selected reaction monitoring mode. The quantification was performed using the isotopically labelled internal standards SAdo-13C4 and SAICAr-13C4, which were prepared via ADSL-catalysed reactions of fumarate-13C4 with adenosine monophosphate and aminoimidazole carboxamide ribotide, respectively, and subsequent alkaline phosphatase-catalysed dephosphorylation of the resulting products. ResultsThe detection of SAICAr and SAdo in DBS was linear over the range of 0–25μmol/L. The respective intra-assay and inter-assay imprecision values were less than 10.7% and 15.2% for SAICAr and 4.7% and 5.7% for SAdo. The recoveries from DBS spiked with different concentrations of SAICAr and SAdo were between 94% and 117%. The concentrations of SAICAr and SAdo were higher in the archived DBS from dADSL patients (SAICAr, 0.03–4.7μmol/L; SAdo, 1.5–21.3μmol/L; n=5) compared to those of the control subjects (SAICAr, 0–0.026μmol/L; SAdo, 0.06–0.14μmol/L; n=31), even after DBSs from dADSL patients were stored for 2–23years. ConclusionsWe developed and validated a method of succinylpurine analysis in DBS that improves selective screening for dADSL in the paediatric population and may be used for retrospective diagnosis to aid the genetic counselling of affected families.

Adenylosuccinate lyase deficiency.

Adenylosuccinate lyase ADSL) deficiency is a defect of purine metabolism affecting purinosome assembly and reducing metabolite fluxes through purine de novo synthesis and purine nucleotide recycling pathways. Biochemically this defect manifests by the presence in the biologic fluids of two dephosphorylated substrates of ADSL enzyme: succinylaminoimidazole carboxamide riboside (SAICAr) and succinyladenosine (S-Ado). More than 80 individuals with ADSL deficiency have been identified, but incidence of the disease remains unknown. The disorder shows a wide spectrum of symptoms from slowly to rapidly progressing forms. The fatal neonatal form has onset from birth and presents with fatal neonatal encephalopathy with a lack of spontaneous movement, respiratory failure, and intractable seizures resulting in early death within the first weeks of life. Patients with type I (severe form) present with a purely neurologic clinical picture characterized by severe psychomotor retardation, microcephaly, early onset of seizures, and autistic features. A more slowly progressing form has also been described (type II, moderate or mild form), as having later onset, usually within the first years of life, slight to moderate psychomotor retardation and transient contact disturbances. Diagnosis is facilitated by demonstration of SAICAr and S-Ado in extracellular fluids such as plasma, cerebrospinal fluid and/or followed by genomic and/or cDNA sequencing and characterization of mutant proteins. Over 50 ADSL mutations have been identified and their effects on protein biogenesis, structural stability and activity as well as on purinosome assembly were characterized. To date there is no specific and effective therapy for ADSL deficiency.

The need for vigilance: False-negative screening for adenylosuccinate lyase deficiency caused by deribosylation of urinary biomarkers

ObjectivesAdenylosuccinate lyase deficiency (dADSL) is a rare inherited metabolic disorder. Biochemical diagnosis of the disease is based on the determination of enormously elevated urinary levels of succinylaminoimidazole carboxamide riboside (SAICA-riboside) and succinyladenosine (SAdo). We report a case of false negative screening for dADSL caused by deribosylation of the urinary biomarkers SAICA-riboside and SAdo. Design and methodsA thin-layer chromatography (TLC) method with Pauly reagent detection of SAICA-riboside was used as a screening method. High-performance liquid chromatography with diode-array detection (HPLC-DAD) and LC–MS/MS methods were used for the identification and quantitative determination of SAICA-riboside, SAdo, succinylaminoimidazole carboxamide (SAICA) and succinyladenine (SA). ResultsFollowing a negative TLC screening in a known case of dADSL, we analyzed urine using HPLC-DAD. The concentration of SAICA-riboside was 2.7mmol/mol creatinine (below the TLC detection limit), and we detected the two abnormal metabolites identified by LC–MS/MS as SAICA and SA. We showed that SAICA and SA were produced by deribosylation of SAICA-riboside and SAdo in the patient's urine. Studies performed by monitoring the production of SAICA and SA after the addition of SAICA-riboside and SAdo to the patient's urine and to urine samples from patients with urinary tract infections suggested that deribosylation is facilitated by bacterial enzymes. ConclusionsScreening methods for the diagnosis of dADSL may be falsely negative due to bacteria-mediated deribosylation of SAICA-riboside and SAdo. HPLC-DAD or LC–MS/MS analyses allowing for simultaneous detection of SAICA-riboside, SAdo and their deribosylation products SAICA and SA should be preferentially used for the diagnosis of dADSL in urine.

Early diagnosis of adenylosuccinate lyase deficiency using a high‐throughput screening method and a trial of oral S‐adenosyl‐l‐methionine as a treatment method

The aim of this study was to develop a high-throughput urine screening technique for adenylosuccinate lyase (ADSL) deficiency and to evaluate S-adenosyl-l-methionine (SAMe) as a potential treatment for this disorder. Testing for succinyladenosine (S-Ado), a marker of ADSL deficiency, was incorporated into a screening panel for urine biomarkers for inborn errors of metabolism using electrospray tandem mass spectrometry. Liquid chromatography-mass spectrometry and high-performance liquid chromatography were used to confirm and monitor the response of metabolites to oral SAMe treatment. Increased levels of S-Ado were detected in a 3-month-old male infant with hypotonia and seizures. ADSL gene sequencing revealed a previously described c.-49T>C mutation and a novel c.889_891dupAAT mutation, which was likely to disrupt enzyme function. After 9 months of SAMe treatment, there was no clear response evidenced in urine metabolite levels or clinical parameters. These results demonstrate proof of the principle for the high-throughput urine screening technique, allowing earlier diagnosis of patients with ADSL deficiency. However, early treatment with SAMe does not appear to be effective in ADSL deficiency. It is suggested that although SAMe treatment may ameliorate purine nucleotide deficiency, it cannot correct metabolic syndromes in which a toxic nucleotide is present, in this case presumed to be succinylaminoimidazole carboxamide ribotide.

Novel proton MR spectroscopy findings in adenylosuccinate lyase deficiency

Adenylosuccinate lyase (ADSL) deficiency is a rare inborn error of metabolism resulting in accumulation of metabolites including succinylaminoimidazole carboxamide riboside (SAICAr) and succinyladenosine (S-Ado) in the brain and other tissues. Patients with ADSL have progressive psychomotor retardation, neonatal seizures, global developmental delay, hypotonia, and autistic features, although variable clinical manifestations may make the initial diagnosis challenging. Two cases of the severe form of the disease are reported here: an 18-month-old boy with global developmental delay, intractable neonatal seizures, progressive cerebral atrophy, and marked hypomyelination, and a 3-month-old girl presenting with microcephaly, neonatal seizures, and marked psychomotor retardation. In both patients in vivo proton magnetic resonance spectroscopy (MRS) showed the presence of S-Ado signal at 8.3 ppm, consistent with a prior report. Interestingly, SAICAr signal was also detectable at 7.5 ppm in affected white matter, which has not been reported in vivo before. A novel splice-site mutation, c.IVS12 + 1/G > C, in the ADSL gene was identified in the second patient. Our findings confirm the utility of in vivo proton MRS in suggesting a specific diagnosis of ADSL deficiency, and also demonstrate an additional in vivo resonance (7.5 ppm) of SAICAr in the cases of severe disease.

Isolated Neonatal Seizures: Adenylosuccinase Deficiency is Another Cause!

I read with great interest the very useful review “Isolated Neonatal Seizures: When to Suspect Inborn Errors of Metabolism” by Ficicioglu and Bearden [ [1] Ficicioglu C. Bearden D. Isolated neonatal seizures: When to suspect inborn errors of metabolism. Pediatr Neurol. 2011; 45: 283-291 Abstract Full Text Full Text PDF PubMed Scopus (31) Google Scholar ]. I would like to add adenylosuccinase deficiency to their causes for suspicion. This genetic, mainly neurologic disorder of the de novo purine synthesis was first reported in 1984 [ [2] Jaeken J. van den Berghe G. An infantile autistic syndrome characterized by the presence of succinylpurines in body fluids. Lancet. 1984; 2: 1058-1061 PubMed Google Scholar ]. Most of the approximately 60 reported patients demonstrate variable associations of moderate to severe psychomotor retardation, epilepsy after their first years, autistic features, and growth retardation [ [3] van den Berghe G. Vincent M.-F. Marie S. Disorders of purine and pyrimidine metabolism. in: Saudubray J.-M. van den Berghe G. Walter J.H. Inborn metabolic diseases: Diagnosis and treatment. 5th ed. Springer-Verlag, Berlin2012: 499-518 Crossref Scopus (11) Google Scholar ]. However, a subgroup of patients presents with intractable seizures beginning within the first days or weeks of age [ [4] Mouchegh K. Zikánová M. Hoffmann G.F. et al. Lethal fetal and early neonatal presentation of adenylosuccinate lyase deficiency: Observation of 6 patients in 4 families. J Pediatr. 2007; 150: 57-61 Abstract Full Text Full Text PDF PubMed Scopus (47) Google Scholar ]. Often severe hypotonia is associated such as seen, e.g., in nonketotic hyperglycinemia and γ-aminobutyric acid transaminase deficiency, as mentioned by Ficicioglu and Bearden [ [1] Ficicioglu C. Bearden D. Isolated neonatal seizures: When to suspect inborn errors of metabolism. Pediatr Neurol. 2011; 45: 283-291 Abstract Full Text Full Text PDF PubMed Scopus (31) Google Scholar ]. These seizures can lead to death or severe mental retardation. In some patients, intrauterine growth retardation, microcephaly, fetal hypokinesia, and a lack of fetal heart rate variability have also been observed. Adenylosuccinase catalyzes two steps in purine synthesis: the conversion of succinyl aminoimidazole carboxamide ribotide to aminoimidazole carboxamide ribotide (in the de novo pathway), and the conversion of adenylosuccinate to adenosine monophosphate. Its deficiency results in the accumulation in body fluids of succinyl purines, i.e., succinyl aminoimidazole carboxamide riboside and succinyl adenosine (the dephosphorylated substrates of the enzyme). A modified Bratton-Marshall (colorimetric) test performed on urine can be used as a screening test, but some medications such as sulfonamides cause a false-positive result. A final diagnosis requires high-pressure liquid chromatography with ultraviolet light detection, or high-pressure liquid chromatography with electrospray ionization tandem mass spectroscopy. Isolated Neonatal Seizures: When to Suspect Inborn Errors of MetabolismPediatric NeurologyVol. 45Issue 5PreviewNeonatal seizures are common, and often comprise the first clinical indicator of central nervous system dysfunction. Although most neonatal seizures are secondary to processes such as hypoxic-ischemic injury, infection, or cortical malformations (which are readily identifiable through routine testing and imaging), seizures secondary to inborn errors of metabolism can be much more difficult to diagnose, and thus a high index of suspicion is required. The early diagnosis of inborn errors of metabolism is crucial, considering that many can receive effective treatment (e.g., dietary supplementation or restriction) with favorable long-term outcomes. Full-Text PDF ResponsePediatric NeurologyVol. 47Issue 3PreviewWe thank Dr. Jaaken for his insightful discussion of adenylosuccinase deficiency as a cause of neonatal seizures. Our review was intended to offer an overview of metabolic disorders presenting with isolated neonatal seizures, i.e., neonatal seizures not associated with other characteristic abnormalities. Dr. Jaaken is correct in observing that neonatal seizures may constitute an atypical presentation of this rare disease, with six cases reported in the literature [1]. However, the severe form of adenylosuccinase deficiency that presents with neonatal seizures is often accompanied by severe hypotonia, intrauterine growth retardation, and magnetic resonance imaging abnormalities that are variable but that generally include dysmyelination [2]. Full-Text PDF

Novel features in the evolution of adenylosuccinate lyase deficiency

BackgroundAdenylosuccinate lyase (ADSL) deficiency is an autosomal recessive disorder of the purine synthesis which results in accumulation of succinylpurines (succinyladenosine (S-Ado) and succinylamino-imidazole carboxamide riboside (SAICAr)) in body fluids. Patients present developmental delay, often accompanied by epilepsy and autistic spectrum disorders. ObjectivesTo describe atypical neurological features in the evolution of three novel unrelated cases of ADSL deficiency. PatientsA 9-year-old boy with severe cognitive impairment and autistic behaviour received d-ribose therapy for one year. Drug withdrawal was associated with acute neurological deterioration, severe brain atrophy and demyelination on MRI. The second patient is a 5.5-year-old girl with mild developmental delay who presented a benign course with moderate cognitive impairment as the only feature in her evolution. The final patient is a 14-year-old boy with severe cognitive impairment who developed drug-resistant epilepsy and bathing reflex seizures, progressive spasticity in the lower limbs and thoracic deformity. MethodsSAICAr and S-Ado in urine were analysed by HPLC with diode array detection. Diagnosis was confirmed by molecular analysis of the ADSL gene. ResultsAn elevation of S-Ado and SAICAr excretion in urine was detected in all three patients. The patients were homozygous for the missence change p.I369L and for the novel change p.M389V. ConclusionDrug-resistant epilepsy and specific therapeutic interventions may modify the neurological outcome in ADSL deficiency. d-ribose must be considered with caution as, in our experience, it returns no clinical benefit and drug withdrawal can precipitate status epilepticus and acute neurological deterioration.

Molecular characterization of the AdeI mutant of Chinese hamster ovary cells: A cellular model of adenylosuccinate lyase deficiency

Adenylosuccinate lyase (ADSL, E. C. 4.3.2.2) carries out two non-sequential steps in de novo AMP synthesis, the conversion of succinylaminoimidazole carboxamide ribotide (SAICAR) to aminoimidazolecarboxamide ribotide (AICAR) and the conversion of succinyl AMP (AMPS) to AMP. In humans, mutations in ADSL lead to an inborn error of metabolism originally characterized by developmental delay, often with autistic features. There is no effective treatment for ADSL deficiency. Hypotheses regarding the pathogenesis include toxicity of high levels of SAICAR, AMPS, or their metabolites, deficiency of the de novo purine biosynthetic pathway, or lack of a completely functional purine cycle in muscle and brain. One important approach to understand ADSL deficiency is to develop cell culture models that allow investigation of the properties of ADSL mutants and the consequences of ADSL deficiency at the cellular level. We previously reported the isolation and initial characterization of mutants of Chinese hamster ovary (CHO-K1) cells ( AdeI) that lack detectable ADSL activity, accumulate SAICAR and AMPS, and require adenine for growth. Here we report the cDNA sequences of ADSL from CHO-K1 and AdeI cells and describe a mutation resulting in an alanine to valine amino acid substitution at position 291 (A291V) in AdeI ADSL. This substitution lies in the “signature sequence” of ADSL, inactivates the enzyme, and validates AdeI as a cellular model of ADSL deficiency.

Clinical, biochemical and molecular findings in seven Polish patients with adenylosuccinate lyase deficiency

Adenylosuccinate lyase (ADSL) catalyzes two steps in purine nucleotide metabolism—the 8th step in the de novo pathway: conversion of succinylaminoimidazole carboxamide ribotide (SAICAR) to aminoimidazole carboxamide ribotide (AICAR), and conversion of adenylosuccinate (S-AMP) to adenylate (AMP) in the purine nucleotide cycle. To date, over 50 patients have been reported suffering from ADSL deficiency. We report all seven so far diagnosed Polish patients with this defect. Most of our patients shared intractable seizures and psychomotor retardation since the neonatal period and had biochemical evidence of severe (type I) deficiency. Two patients with type II suffered only from mild/moderate psychomotor retardation and showed a transientvisual contact disturbance. One patient had a fatal neonatal form of ADSL deficiency with lack of spontaneous movement, respiratory failure, severe encephalopathy and intractable seizures. Analysis of the ADSL gene showed that four apparently unrelated patients carried a R426H mutation (two homozygous and two compound heterozygous). With the exception of the latter mutation, a Y114H mutation that had been reported previously, and a novel mutation T242I, all other mutations (including D268H and three novel S23R, D215H and I351T mutations) were found only in single families in single alleles. A search for this disorder should be included in the screening program of all infants with unexplained neonatal seizures, severe infantile epileptic encephalopathy, developmental delay, hypotonia, and/or autistic features.

Adenylosuccinate lyase deficiency: The first identified polish patient

Adenylosuccinate lyase (ADSL) deficiency is a rare disease of de novo purine synthesis. The main symptoms are psychomotor retardation, epilepsy, autistic features, occasionally associated with muscular hypotonia. Diagnosis is made by detection of abnormal purine metabolites (succinyladenosine – S-Ado and succinylaminoimidazole carboxamide riboside – SAICAr) in body fluids. The severity of the clinical features correlates with low S-Ado/SAICAr ratio. We report clinical, biochemical and brain MRI findings of a female infant with severe early epilepsy and hypotonia, who died at the age of 10 weeks.

The characterization of mutant Bacillus subtilis adenylosuccinate lyases corresponding to severe human adenylosuccinate lyase deficiencies.

Adenylosuccinate lyase is a homotetramer that catalyzes two discrete reactions in the de novo synthesis of purines: the cleavage of adenylosuccinate and succinylaminoimidazole carboxamide ribotide (SAICAR). Several point mutations in the gene encoding the enzyme have been implicated in human disease. Bacillus subtilis adenylosuccinate lyase was used as a model system in which mutations were constructed corresponding to those mutations associated with severe human adenylosuccinate lyase deficiency. Site-directed mutagenesis was utilized to construct amino acid substitutions in B. subtilis adenylosuccinate lyase; Met(10), Ile(123), and Thr(367) were replaced by Leu, Trp, and Arg, respectively, and the altered enzymes were expressed in Escherichia coli. These purified enzymes containing amino acid substitutions were found to have substantial catalytic activity and exhibit relatively small changes in their kinetic parameters. The major deviations from the wild-type-like behavior were observed upon biophysical characterization. All of these enzymes with amino acid replacements are associated with marked thermal instability. I123W adenylosuccinate lyase exhibits notable changes in the circular dichroism spectra, and a native gel electrophoresis pattern indicative of some protein aggregation. T367R also exhibits alterations at the quarternary level, as reflected in native gel electrophoresis. Experimental results, combined with homology modeling, suggest that the altered enzymes are primarily structurally impaired. The enzyme instability was found to be lessened by subunit complementation with the wild-type enzyme, under mild conditions; these studies may have implications for the in vivo behavior of adenylosuccinate lyase in heterozygous patients. Residues Met(10), Ile(123), and Thr(367) appear to be located in regions of the enzyme important for maintaining the structural integrity required for a stable, functional enzyme.

Clinical, biochemical and molecular genetic correlations in adenylosuccinate lyase deficiency.

Adenylosuccinate lyase (ADSL) deficiency (MIM 103050) is an autosomal recessive inborn error of purine synthesis characterized by the accumulation in body fluids of succinylaminoimidazolecarboxamide (SAICA) riboside and succinyladenosine (S-Ado), the dephosphorylated derivatives of the two substrates of the enzyme. Because ADSL-deficient patients display widely variable degrees of psychomotor retardation, we have expressed eight mutated ADSL enzymes as thioredoxin fusions and compared their properties with the clinical and biochemical characteristics of 10 patients. Three expressed mutated ADSL enzymes (M26L, R426H and T450S) were thermolabile, four (A2V, R141W, R303C and S395R) were thermostable and one (del206-218), was inactive. Thermolabile mutations decreased activities with SAICA ribotide (SAICAR) and adenylosuccinate (S-AMP) in parallel, or more with SAICAR than with S-AMP. Patients homozygous for one of these mutations, R426H, displayed similarly decreased ADSL activities in their fibroblasts, S-Ado:SAICA riboside ratios of approximately 1 in their cerebrospinal fluid and were profoundly retarded. With the exception of A2V, thermostable mutations decreased activity with S-AMP to a much more marked extent than with SAICAR. Two unrelated patients homozygous for one of the thermostable mutations, R303C, also displayed a much more marked decrease in the activity of fibroblast ADSL with S-AMP than with SAICAR, had S-Ado:SAICA riboside ratios between 3 and 4 in their cerebrospinal fluid and were mildly retarded. These results suggest that, in some cases, the genetic lesion of ADSL determines the ratio of its activities with S-AMP versus SAICAR, which in turn defines the S-Ado:SAICA riboside ratio and the patients' mental status.

Adenylosuccinase deficiency: possibly underdiagnosed encephalopathy with variable clinical features

Adenylosuccinase deficiency is an autosomal recessive inherited defect of purine synthesis. In enzyme deficient patients, two normally undetectable compounds, succinylaminoimidazole carboxamide riboside and succinyladenosine, accumulate in urine, cerebrospinal fluid and, to a minor extent, in plasma. Analysing 150 highly selected urine specimens from patients with unidentified neurogenerative disorders we discovered the first two German cases of adenylosuccinase deficiency. The deficiency causes moderate to severe mental retardation, often accompanied by epileptic seizures and/or autistic features, and is occasionally associated with growth retardation and muscular hypotonia. Of the two German cases we present here, one patient fits into the clinical picture outlined by previous reports. The other patient, however, shows a pattern of symptoms so far undescribed: severe early infantile epileptic encephalopathy with reduced myelination. On mutation analysis this patient is the first to reveal a 39 base pair deletion in the adenylosuccinase gene in contrast to the point mutations detected in previous cases. Adenylosuccinase deficiency may be an underdiagnosed metabolic disorder with variable expression. This should be taken into consideration in patients with unclassified neurological conditions.

Muscle energy metabolism in human adenylosuccinase deficiency. An in vivo 31P-NMR spectroscopy study.

Adenylosuccinate lyase (EC 4.3.2.2; ASase) catalyses two steps in the synthesis of purine nucleotides: the conversion of succinylaminoimidazole carboxamide (SAICA) ribotide into aminoimidazole carboxamide (AICA) ribotide along the de novo pathway and the formation of AMP from adenylosuccinate in the conversion of IMP into adenine nucleotides. Both reactions involve the cleavage of a succinyl group, yielding fumarate.1

Succinylpurines induce neuronal damage in the rat brain.

Adenylosuccinase (adenylosuccinate lyase, EC 4.3.2.2: ASase) catalyses two steps in the purine metabolic pathways: a) the eighth step in the de novo pathway of purine synthesis: conversion of succinylaminoimidazole carboxamide ribotide (SAICAR) into aminoimidazole carboxamide ribotide (AICAR) and b) the second step in the formation of adenyl nucleotides from IMP: conversion of adenylosuccinate (S-AMP) into AMP. As a result of the enzyme deficiency, there is a recognised accumulation of the two dephosphorylated substrates of the enzyme: SAICA riboside and succinyladenosine (S-Ado). Dephosphorylation of SAICAR and S-AMP is performed by cytosolic 5′nucleotidases. Neither SAICA riboside nor S-Ado are normally detectable in the blood or tissue samples of humans, but in patients with ASase deficiency, both compounds are present in the urine, blood and CSF. In the latter, concentrations are usually around 100-200 μM (Jaeken et al., 1993).

Succinylpurines do not modify glutamate or adenosine effects in the CNS.

Children suffering from deficiency of adenylosuccinase (adenylosuccinate lyase, EC 4.3.2.2: ASase) are normal at birth, but profound psychomotor retardation, the principal symptom of the defect, becomes evident in the first two years (Jaeken & van den Berghe, 1984). The clinical picture is markedly heterogeneous, often manifesting epilepsy and autistic features, sometimes muscle wasting and growth failure (Jaeken et al., 1988). There is a recognised accumulation of the two dephosphorylated substrates of the enzyme: succinyl-aminoimidazole carboxamide riboside (SAICA riboside) and succinyladenosine (S-Ado). Dephosphorylation of SAICA ribotide and adenylsuccinate is performed by cytosolic 5′-nucleotidases. Neither SAICA riboside nor S-Ado are normally detectable in the blood or tissue samples of humans, but in patients with ASase deficiency, both compounds are present in the urine, blood and CSF. In the CSF, concentrations are frequently around 100–200 μM (Jaeken et al., 1993).