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

Identification of the Third Patient With PAICS Deficiency Harbouring the p.(Lys53Arg) Recurrent Variant, Extending the Phenotype Diversity

Phosphoribosylaminoimidazole carboxylase (PAICS) deficiency, caused by biallelic variants in PAICS gene, is an inborn error of de novo purine synthesis. Only two patients from a consanguineous family have been reported, with multiple congenital malformations, resulting in early neonatal death. Molecular analysis identified a homozygous p.(Lys53Arg) missense variant. We report the third case of PAICS deficiency in a 7 years old boy, presenting with polymalformative syndrome, but normal neurodevelopment. We report malformations not previously described in PAICS deficiency, notably congenital cardiopathy, and support the consistency of skeletal and oesophageal defects. Genome Sequencing identified the homozygous pathogenic variant p.(Lys53Arg), suggesting a recurrent variant in PAICS. A probable recurrence of PAICS deficiency occurred in a sibling, with a similar polymalformative syndrome antenatally diagnosed, but could not be confirmed molecularly. We further delineate the phenotype of PAICS deficiency and provide new insights concerning prognosis, notably in terms of neurodevelopment.

The diagnosis and treatment of disorders of nucleic acid/nucleotide metabolism associated with epilepsy

Epilepsy is a prevalent paroxysmal disorder in the field of neurology. Among the six etiologies of epilepsy, metabolic causes are relatively uncommon in clinical practice. Metabolic disorders encompass amino acid metabolism disorders, organic acid metabolism disorders, and other related conditions. Seizures resulting from nucleic acid/nucleotide metabolism disorders are even more infrequent. This review provides an overview of several studies on nucleic acid/nucleotide metabolism disorders associated with epilepsy, including adenosine succinate lyase deficiency, Lesch-Nyhan syndrome, and aminoimidazole carboxamide ribonucleotide transformylase/inosine monophosphate cyclohydrolase (ATIC) deficiency, among others. The potential pathogenesis, phenotypic features, diagnostic pathways, and therapeutic approaches of these diseases are discussed in this review. The goal is to help clinicians make an accurate diagnosis when encountering rare nucleic acid/nucleotide metabolism disorders with multi-system symptoms and manifestations of epilepsy.

The Spectrum of Disease-Associated Alleles in Countries with a Predominantly Slavic Population

There are more than 260 million people of Slavic descent worldwide, who reside mainly in Eastern Europe but also represent a noticeable share of the population in the USA and Canada. Slavic populations, particularly Eastern Slavs and some Western Slavs, demonstrate a surprisingly high degree of genetic homogeneity, and, consequently, remarkable contribution of recurrent alleles associated with hereditary diseases. Along with pan-European pathogenic variants with clearly elevated occurrence in Slavic people (e.g., ATP7B c.3207C>A and PAH c.1222C>T), there are at least 52 pan-Slavic germ-line mutations (e.g., NBN c.657_661del and BRCA1 c.5266dupC) as well as several disease-predisposing alleles characteristic of the particular Slavic communities (e.g., Polish SDHD c.33C>A and Russian ARSB c.1562G>A variants). From a clinical standpoint, Slavs have some features of a huge founder population, thus providing a unique opportunity for efficient genetic studies.

A Caenorhabditis elegans model of adenylosuccinate lyase deficiency reveals neuromuscular and reproductive phenotypes of distinct etiology

Inborn errors of purine metabolism are rare syndromes with an array of complex phenotypes in humans. One such disorder, adenylosuccinate lyase deficiency (ASLD), is caused by a decrease in the activity of the bi-functional purine biosynthetic enzyme adenylosuccinate lyase (ADSL). Mutations in human ADSL cause epilepsy, muscle ataxia, and autistic-like symptoms. Although the genetic basis of ASLD is known, the molecular mechanisms driving phenotypic outcome are not. Here, we characterize neuromuscular and reproductive phenotypes associated with a deficiency of adsl-1 in Caenorhabditis elegans. We demonstrate that adsl-1 function contributes to regulation of spontaneous locomotion, that adsl-1 functions acutely for proper mobility, and that aspects of adsl-1-related dysfunction are reversible. Using pharmacological supplementation, we correlate phenotypes with distinct metabolic perturbations. The neuromuscular defect correlates with accumulation of a purine biosynthetic intermediate whereas reproductive deficiencies can be ameliorated by purine supplementation, indicating differing molecular mechanisms behind the phenotypes. Because purine metabolism is highly conserved in metazoans, we suggest that similar separable metabolic perturbations result in the varied symptoms in the human disorder and that a dual-approach therapeutic strategy may be beneficial.

Purine Biosynthesis Pathways Are Required for Myogenesis in Xenopus laevis

Purines are required for fundamental biological processes and alterations in their metabolism lead to severe genetic diseases associated with developmental defects whose etiology remains unclear. Here, we studied the developmental requirements for purine metabolism using the amphibian Xenopus laevis as a vertebrate model. We provide the first functional characterization of purine pathway genes and show that these genes are mainly expressed in nervous and muscular embryonic tissues. Morphants were generated to decipher the functions of these genes, with a focus on the adenylosuccinate lyase (ADSL), which is an enzyme required for both salvage and de novo purine pathways. adsl.L knockdown led to a severe reduction in the expression of the myogenic regulatory factors (MRFs: Myod1, Myf5 and Myogenin), thus resulting in defects in somite formation and, at later stages, the development and/or migration of both craniofacial and hypaxial muscle progenitors. The reduced expressions of hprt1.L and ppat, which are two genes specific to the salvage and de novo pathways, respectively, resulted in similar alterations. In conclusion, our data show for the first time that de novo and recycling purine pathways are essential for myogenesis and highlight new mechanisms in the regulation of MRF gene expression.

Improved diagnostics of purine and pyrimidine metabolism disorders using LC-MS/MS and its clinical application

OBJECTIVES

To develop a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to quantify 41 different purine and pyrimidine (PuPy) metabolites in human urine to allow detection of most known disorders in this metabolic pathway and to determine reference intervals.

METHODS

Urine samples were diluted with an aqueous buffer to minimize ion suppression. For detection and quantification, liquid chromatography was combined with electrospray ionization, tandem mass spectrometry and multiple reaction monitoring. Transitions and instrument settings were established to quantify 41 analytes and nine stable-isotope-labeled internal standards (IS).

RESULTS

The established method is precise (intra-day CV: 1.4-6.3%; inter-day CV: 1.3-15.2%), accurate (95.2% external quality control results within ±2 SD and 99.0% within ±3 SD; analyte recoveries: 61-121%), sensitive and has a broad dynamic range to quantify normal and pathological metabolite concentrations within one run. All analytes except aminoimidazole ribonucleoside (AIr) are stable before, during and after sample preparation. Moreover, analytes are not affected by five cycles of freeze-thawing (variation: -5.6 to 7.4%), are stable in thymol (variation: -8.4 to 12.9%) and the lithogenic metabolites also in HCl conserved urine. Age-dependent reference intervals from 3,368 urine samples were determined and used to diagnose 11 new patients within 7 years (total performed tests: 4,206).

CONCLUSIONS

The presented method and reference intervals enable the quantification of 41 metabolites and the potential diagnosis of up to 25 disorders of PuPy metabolism.

Inborn errors of purine and pyrimidine metabolism: A guide to diagnosis

Inborn errors of purine and pyrimidine (P/P) metabolism are under-reported and rarely mentioned in the general literature or in clinical practice, as well as in reviews dedicated to other inborn errors of metabolism (IEMs). However, their diagnosis is important because genetic counseling can be provided and, in some cases, specific treatment exists that may slow or even reverse clinical signs. The purpose of this review is to provide a practical guideline on the suspicion and investigation of inborn errors of P/P metabolism. Failure of a physician to recognize the presence of these disorders may be devastating for affected infants and children because of its permanent effects in the patient, and for their parents because of implications for future offspring. Diagnosis is crucial because genetic counseling can be provided and, in some cases, specific treatment can be offered that may slow or even reverse clinical symptoms. This review highlights the risk factors in the history, the important examination findings, and the appropriate biochemical investigation of the child. Herein we describe the approach to the diagnosis of P/P disorders and emphasize clinical situations in which physicians should consider these diseases as diagnostic possibilities.

Prenatal risk factors and genetic causes of ADHD in children

BACKGROUND

Attention deficit/hyperactivity disorder (ADHD) is a common disease among children; it affected 5-7% of the population in 2015. ADHD is a multifactorial disease, and its etiology is still not clearly understood.

DATA SOURCES

This narrative review has been done by searching the PubMed and Embase databases using attention deficit/hyperactivity disorder, ADHD, risk factors; genetics; pediatrics; psychiatrics as keywords.

RESULTS

ADHD is considered to be a hereditary disorder in which genes play the fundamental role in the pathogenesis; however, findings from genetic-environmental studies support the hypothesis that genetic factors can exert effects on an individual's condition by determining his/her responses to environmental exposures, especially those during the prenatal stage.

CONCLUSION

ADHD is considered as a hereditary disorder in which genes and prenatal risk factors play fundamental roles in the pathogenesis.

Combined Targeted and Untargeted Profiling of HeLa Cells Deficient in Purine De Novo Synthesis

Three genetically determined enzyme defects of purine de novo synthesis (PDNS) have been identified so far in humans: adenylosuccinate lyase (ADSL) deficiency, 5-amino-4-imidazole carboxamide-ribosiduria (AICA-ribosiduria), and deficiency in bifunctional enzyme phosphoribosylaminoimidazole carboxylase and phosphoribosylaminoimidazolesuccinocarboxamide synthase (PAICS). Clinical signs of these defects are mainly neurological, such as seizures, psychomotor retardation, epilepsy, autistic features, etc. This work aims to describe the metabolic changes of CRISPR-Cas9 genome-edited HeLa cells deficient in the individual steps of PDNS to better understand known and potential defects of the pathway in humans. High-performance liquid chromatography coupled with mass spectrometry was used for both targeted and untargeted metabolomic analyses. The statistically significant features from the untargeted study were identified by fragmentation analysis. Data from the targeted analysis were processed in Cytoscape software to visualize the most affected metabolic pathways. Statistical significance of PDNS intermediates preceding deficient enzymes was the highest (p-values 10 × 10−7–10 × 10−15) in comparison with the metabolites from other pathways (p-values of up to 10 × 10−7). Disturbed PDNS resulted in an altered pool of adenine and guanine nucleotides. However, the adenylate energy charge was not different from controls. Different profiles of acylcarnitines observed among deficient cell lines might be associated with a specific enzyme deficiency rather than global changes related to the PDNS pathway. Changes detected in one-carbon metabolism might reduce the methylation activity of the deficient cells, thus affecting the modification state of DNA, RNA, and proteins.

Pathway-specific effects of ADSL deficiency on neurodevelopment

Adenylosuccinate lyase (ADSL) functions in de novo purine synthesis (DNPS) and the purine nucleotide cycle. ADSL deficiency (ADSLD) causes numerous neurodevelopmental pathologies, including microcephaly and autism spectrum disorder. ADSLD patients have normal serum purine nucleotide levels but exhibit accumulation of dephosphorylated ADSL substrates, S-Ado, and SAICAr, the latter being implicated in neurotoxic effects through unknown mechanisms. We examined the phenotypic effects of ADSL depletion in human cells and their relation to phenotypic outcomes. Using specific interventions to compensate for reduced purine levels or modulate SAICAr accumulation, we found that diminished AMP levels resulted in increased DNA damage signaling and cell cycle delays, while primary ciliogenesis was impaired specifically by loss of ADSL or administration of SAICAr. ADSL-deficient chicken and zebrafish embryos displayed impaired neurogenesis and microcephaly. Neuroprogenitor attrition in zebrafish embryos was rescued by pharmacological inhibition of DNPS, but not increased nucleotide concentration. Zebrafish also displayed phenotypes commonly linked to ciliopathies. Our results suggest that both reduced purine levels and impaired DNPS contribute to neurodevelopmental pathology in ADSLD and that defective ciliogenesis may influence the ADSLD phenotypic spectrum.

Cellular and molecular mechanisms underlying autism spectrum disorders and associated comorbidities: A pathophysiological review

Autism spectrum disorders (ASD) are a group of neurodevelopmental disorders that develop in early life due to interaction between several genetic and environmental factors and lead to alterations in brain function and structure. During the last decades, several mechanisms have been placed to explain the pathogenesis of autism. Unfortunately, these are reported in several studies and reviews which make it difficult to follow by the reader. In addition, some recent molecular mechanisms related to ASD have been unrevealed. This paper revises and highlights the major common molecular mechanisms responsible for the clinical symptoms seen in people with ASD, including the roles of common genetic factors and disorders, neuroinflammation, GABAergic signaling, and alterations in Ca⁺² signaling. Besides, it covers the major molecular mechanisms and signaling pathways involved in initiating the epileptic seizure, including the alterations in the GABAergic and glutamate signaling, vitamin and mineral deficiency, disorders of metabolism, and autoimmunity. Finally, this review also discusses sleep disorder patterns and the molecular mechanisms underlying them.

High prevalence of multilocus pathogenic variation in neurodevelopmental disorders in the Turkish population

Neurodevelopmental disorders (NDDs) are clinically and genetically heterogenous; many such disorders are secondary to perturbation in brain development and/or function. The prevalence of NDDs is > 3%, resulting in significant sociocultural and economic challenges to society. With recent advances in family-based genomics, rare-variant analyses, and further exploration of the Clan Genomics hypothesis, there has been a logarithmic explosion in neurogenetic "disease-associated genes" molecular etiology and biology of NDDs; however, the majority of NDDs remain molecularly undiagnosed. We applied genome-wide screening technologies, including exome sequencing (ES) and whole-genome sequencing (WGS), to identify the molecular etiology of 234 newly enrolled subjects and 20 previously unsolved Turkish NDD families. In 176 of the 234 studied families (75.2%), a plausible and genetically parsimonious molecular etiology was identified. Out of 176 solved families, deleterious variants were identified in 218 distinct genes, further documenting the enormous genetic heterogeneity and diverse perturbations in human biology underlying NDDs. We propose 86 candidate disease-trait-associated genes for an NDD phenotype. Importantly, on the basis of objective and internally established variant prioritization criteria, we identified 51 families (51/176 = 28.9%) with multilocus pathogenic variation (MPV), mostly driven by runs of homozygosity (ROHs) - reflecting genomic segments/haplotypes that are identical-by-descent. Furthermore, with the use of additional bioinformatic tools and expansion of ES to additional family members, we established a molecular diagnosis in 5 out of 20 families (25%) who remained undiagnosed in our previously studied NDD cohort emanating from Turkey.

Rett Syndrome Spectrum in Monogenic Developmental-Epileptic Encephalopathies and Epilepsies: A Review

INTRODUCTION

Progress in the clinical application of next-generation-sequencing-based techniques has resulted in a dramatic increase in the recognized genetic heterogeneity of the Rett syndrome spectrum (RSS). Our awareness of the considerable overlap with pediatric-onset epilepsies and epileptic/developmental encephalopathies (EE/DE) genes is also growing, and the presence of variable clinical features inside a general frame of commonalities has drawn renewed attention into deep phenotyping.

METHODS

We decided to review the medical literature on atypical Rett syndrome and "Rett-like" phenotypes, with special emphasis on described cases with pediatric-onset epilepsies and/or EE-DE, evaluating Neul's criteria for Rett syndrome and associated movement disorders and notable stereotypies.

RESULTS

"Rett-like" features were described in syndromic and non-syndromic monogenic epilepsy- and DE/EE-related genes, in "intellectual disability plus epilepsy"-related genes and in neurodegenerative disorders. Additionally, prominent stereotypies can be observed in monogenic complex neurodevelopmental disorders featuring epilepsy with or without autistic features outside of the RSS.

CONCLUSIONS

Patients share a complex neurodevelopmental and neurological phenotype (developmental delay, movement disorder) with impaired gait, abnormal tone and hand stereotypies. However, the presence and characteristics of regression and loss of language and functional hand use can differ. Finally, the frequency of additional supportive criteria and their distribution also vary widely.

Clinical and molecular characterization of patients with adenylosuccinate lyase deficiency

Background

Adenylosuccinate lyase deficiency (ADSLD) is an ultrarare neurometabolic recessive disorder caused by loss-of-function mutations in the ADSL gene. The disease is characterized by wide clinical variability. Here we provide an updated clinical profiling of the disorder and discuss genotype–phenotype correlations.

Results

Data were collected through "Our Journey with ADSL deficiency Association" by using a dedicated web survey filled-in by parents.

Clinical and molecular data were collected from 18 patients (12 males, median age 10.9 years ± 7.3), from 13 unrelated families. The age at onset ranged from birth to the first three years (median age 0.63 years ± 0.84 SD), and age at diagnosis varied from 2 months to 17 years, (median age 6.4 years ± 6.1 SD). The first sign was a psychomotor delay in 8/18 patients, epilepsy in 3/18, psychomotor delay and epilepsy in 3/18, and apneas, hypotonia, nystagmus in single cases. One patient (sibling of a previously diagnosed child) had a presymptomatic diagnosis. The diagnosis was made by exome sequencing in 7/18 patients. All patients were definitively diagnosed with ADSL deficiency based on pathogenic variants and/or biochemical assessment. One patient had a fatal neonatal form of ADSL deficiency, seven showed features fitting type I, and nine were characterized by a milder condition (type II), with two showing a very mild phenotype. Eighteen different variants were distributed along the entire ADSL coding sequence and were predicted to have a variable structural impact by impairing proper homotetramerization or catalytic activity of the enzyme. Six variants had not previously been reported. All but two variants were missense.

Conclusions

The study adds more details on the spectrum of ADSLD patients’ phenotypes and molecular data.

Myoclonic tremor status as a presenting symptom of adenylosuccinate lyase deficiency

Adenylosuccinate lyase deficiency is a rare autosomal recessive disorder of purine metabolism. The disorder manifests with developmental delay, postnatal microcephaly, hypotonia, involuntary movements, epileptic seizures, ataxia and autistic features. Paroxysmal non-epileptic motor events are not a typical presentation of the disease. We describe an 8-year-old boy who presented with an infantile onset of prolonged episodes of multifocal sustained myoclonic tremor lasting from minutes to days on a background of global developmental delay and gait ataxia. Ictal EEG during these episodes was normal. Ictal surface EMG of the involved upper limb showed a muscular activation pattern consistent with cortical myoclonus. Brain MRI showed mild cerebral atrophy. Whole exome sequencing revealed a novel homozygous variant in the ADSL gene: c.1027G > A; p. Glu343Lys, inherited from each heterozygous parent. There was a marked elevation of urine succinyladenosine, confirming the diagnosis of adenylosuccinate lyase deficiency. In conclusion, myoclonic tremor status expands the spectrum of movement disorders seen in adenylosuccinate lyase deficiency.

Broadening phenotype of adenylosuccinate lyase deficiency: A novel clinical pattern resembling neuronal ceroid lipofuscinosis

We describe a 7-year-old boy presenting with a developmental encephalopathy, severe epilepsy, retinopathy with salt and pepper fundus, and ultrastructural skin alterations resembling a neuronal ceroid lipofuscinosis. Whole exome-sequencing detected biallelic variants in the ADSL gene (c.65C > T [p.(Ala22Val)] and c.340 T > C [p.(Tyr114His)]). The increase of SAICAR and S-Ado in blood and urine was consistent with the pattern of adenylosuccinate lyase deficiency (OMIM 103050). An unusual increase of AICAR, that was due to a residual ADSL enzyme activity of about 28%, was also detected.

Neither salt and pepper retinopathy nor ultrastructural skin alterations had been reported in ADSL deficiency before. Impaired purinergic signaling inside the retina is probably involved in visual failure. Ultrastructural alterations in fibroblasts suggest a possible damage of autophagic processes, whose role in the pathogenesis of neurological dysfunction deserves further study.

Purine Homeostasis Is Necessary for Developmental Timing, Germline Maintenance and Muscle Integrity in Caenorhabditis elegans

Purine homeostasis is ensured through a metabolic network widely conserved from prokaryotes to humans. Purines can either be synthesized de novo, reused, or produced by interconversion of extant metabolites using the so-called recycling pathway. Although thoroughly characterized in microorganisms, such as yeast or bacteria, little is known about regulation of the purine biosynthesis network in metazoans. In humans, several diseases are linked to purine metabolism through as yet poorly understood etiologies. Particularly, the deficiency in adenylosuccinate lyase (ADSL)-an enzyme involved both in the purine de novo and recycling pathways-causes severe muscular and neuronal symptoms. In order to address the mechanisms underlying this deficiency, we established Caenorhabditis elegans as a metazoan model organism to study purine metabolism, while focusing on ADSL. We show that the purine biosynthesis network is functionally conserved in C. elegans Moreover, adsl-1 (the gene encoding ADSL in C. elegans) is required for developmental timing, germline stem cell maintenance and muscle integrity. Importantly, these traits are not affected when solely the de novo pathway is abolished, and we present evidence that germline maintenance is linked specifically to ADSL activity in the recycling pathway. Hence, our results allow developmental and tissue specific phenotypes to be ascribed to separable steps of the purine metabolic network in an animal model.

Yeast to Study Human Purine Metabolism Diseases

Purine nucleotides are involved in a multitude of cellular processes, and the dysfunction of purine metabolism has drastic physiological and pathological consequences. Accordingly, several genetic disorders associated with defective purine metabolism have been reported. The etiology of these diseases is poorly understood and simple model organisms, such as yeast, have proved valuable to provide a more comprehensive view of the metabolic consequences caused by the identified mutations. In this review, we present results obtained with the yeast Saccharomyces cerevisiae to exemplify how a eukaryotic unicellular organism can offer highly relevant information for identifying the molecular basis of complex human diseases. Overall, purine metabolism illustrates a remarkable conservation of genes, functions and phenotypes between humans and yeast.

Plausibility of the zebrafish embryos/larvae as an alternative animal model for autism: A comparison study of transcriptome changes

Autism spectrum disorder (ASD) is a serious neurodevelopmental disorder characterized by impaired or abnormal social interaction and communication and by restricted and repetitive behaviour. ASD is highly prevalent in Asia, Europe, and the United States, and the frequency of ASD is growing each year. Recent epidemiological studies have indicated that ASD may be caused or triggered by exposure to chemicals in the environment, such as those in the air or water. Thus, toxicological studies are needed to examine chemicals that might be implicated. However, the experimental efficiency of existing experimental models is limited, and many models represent challenges in terms of animal welfare. Thus, alternative ASD animal models are necessary. To address this, we examined the efficacy of the zebrafish embryo/larva as an alternative model of ASD. Specifically, we exposed zebrafish to valproic acid (0, 12.5, 25, 50, or 100 μM), which is a chemical known to induce autism-like effects. We then analysed subsequent developmental, behavioural, and transcriptomic changes. We found that 100 μM and 50 μM valproic acid decreased the hatching rate and locomotor activity of zebrafish embryos/larvae. Transcriptomic analysis revealed significant alterations in a number of genes associated with autism, such as adsl, mbd5, shank3, and tsc1b. Additionally, we found changes in gene ontology that were also reported in previous studies. Our findings indicate that zebrafish embryos/larvae and humans with ASD might have common physiological pathways, indicating that this animal model may represent an alternative tool for examining the causes of and potential treatments for this illness.

Cryptococcus neoformans ADS lyase is an enzyme essential for virulence whose crystal structure reveals features exploitable in antifungal drug design

There is significant clinical need for new antifungal agents to manage infections with pathogenic species such as Cryptococcus neoformans Because the purine biosynthesis pathway is essential for many metabolic processes, such as synthesis of DNA and RNA and energy generation, it may represent a potential target for developing new antifungals. Within this pathway, the bifunctional enzyme adenylosuccinate (ADS) lyase plays a role in the formation of the key intermediates inosine monophosphate and AMP involved in the synthesis of ATP and GTP, prompting us to investigate ADS lyase in C. neoformans. Here, we report that ADE13 encodes ADS lyase in C. neoformans. We found that an ade13Δ mutant is an adenine auxotroph and is unable to successfully cause infections in a murine model of virulence. Plate assays revealed that production of a number of virulence factors essential for dissemination and survival of C. neoformans in a host environment was compromised even with the addition of exogenous adenine. Purified recombinant C. neoformans ADS lyase shows catalytic activity similar to its human counterpart, and its crystal structure, the first fungal ADS lyase structure determined, shows a high degree of structural similarity to that of human ADS lyase. Two potentially important amino acid differences are identified in the C. neoformans crystal structure, in particular a threonine residue that may serve as an additional point of binding for a fungal enzyme-specific inhibitor. Besides serving as an antimicrobial target, C. neoformans ADS lyase inhibitors may also serve as potential therapeutics for metabolic disease; rather than disrupt ADS lyase, compounds that improve the stability the enzyme may be used to treat ADS lyase deficiency disease.

Structural and kinetic analysis of Schistosoma mansoni Adenylosuccinate Lyase (SmADSL)

Schistosoma mansoni is the parasite responsible for schistosomiasis, a disease that affects about 218 million people worldwide. Currently, both direct treatment and disease control initiatives rely on chemotherapy using a single drug, praziquantel. Concerns over the possibility of resistance developing to praziquantel, have stimulated efforts to develop new drugs for the treatment of schistosomiasis. Schistosomes do not have the de novo purine biosynthetic pathway, and instead depend entirely on the purine salvage pathway to supply its need for purines. The purine salvage pathway has been reported as a potential target for developing new drugs against schistosomiasis. Adenylosuccinate lyase (SmADSL) is an enzyme in this pathway, which cleaves adenylosuccinate (ADS) into adenosine 5'-monophosphate (AMP) and fumarate. SmADSL kinetic characterization was performed by isothermal titration calorimetry (ITC) using both ADS and SAICAR as substrates. Structures of SmADSL in Apo form and in complex with AMP were elucidated by x-ray crystallography revealing a highly conserved tetrameric structure required for their function since the active sites are formed from residues of three different subunits. The active sites are also highly conserved between species and it is difficult to identify a potent species-specific inhibitor for the development of new therapeutic agents. In contrast, several mutagenesis studies have demonstrated the importance of dimeric interface residues in the stability of the quaternary structure of the enzyme. The lower conservation of these residues between SmADSL and human ADSL could be used to lead the development of anti-schistosomiasis drugs based on disruption of subunit interfaces. These structures and kinetics data add another layer of information to Schistosoma mansoni purine salvage pathway.

Can psychiatric childhood disorders be due to inborn errors of metabolism?

Many patients who visit a centre for hereditary metabolic diseases remarkably also suffer from a child psychiatric disorder. Those child psychiatric disorders may be the first sign or manifestation of an underlying metabolic disorder. Lack of knowledge of metabolic disorders in child psychiatry may lead to diagnoses being missed. Patients therefore are also at risk for not accessing efficacious treatment and proper counselling. To search the literature for the co-occurrence of child psychiatric disorders, such as ADHD, autism, psychosis, learning disorders and eating disorders and metabolic disorders. A search of the literature was conducted by performing a broad search on PubMed, using the terms "ADHD and metabolic disorders", "autism and metabolic disorders", "psychosis and metabolic disorders", "learning disorders and metabolic disorders", and "eating disorders and metabolic disorders". Based on inclusion criteria (concerning a clear psychiatric disorder and concerning a metabolic disorder) 4441 titles and 249 abstracts were screened and resulted in 71 relevant articles. This thorough literature search provides child and adolescent psychiatrists with an overview of metabolic disorders associated with child psychiatric symptoms, their main characteristics and recommendations for further investigations.

Diagnosis of adenylosuccinate lyase deficiency by metabolomic profiling in plasma reveals a phenotypic spectrum

Adenylosuccinate lyase (ADSL) deficiency is a rare autosomal recessive neurometabolic disorder that presents with a broad-spectrum of neurological and physiological symptoms. The ADSL gene produces an enzyme with binary molecular roles in de novo purine synthesis and purine nucleotide recycling. The biochemical phenotype of ADSL deficiency, accumulation of SAICAr and succinyladenosine (S-Ado) in biofluids of affected individuals, serves as the traditional target for diagnosis with targeted quantitative urine purine analysis employed as the predominate method of detection. In this study, we report the diagnosis of ADSL deficiency using an alternative method, untargeted metabolomic profiling, an analytical scheme capable of generating semi-quantitative z-score values for over 1000 unique compounds in a single analysis of a specimen. Using this method to analyze plasma, we diagnosed ADSL deficiency in four patients and confirmed these findings with targeted quantitative biochemical analysis and molecular genetic testing. ADSL deficiency is part of a large a group of neurometabolic disorders, with a wide range of severity and sharing a broad differential diagnosis. This phenotypic similarity among these many inborn errors of metabolism (IEMs) has classically stood as a hurdle in their initial diagnosis and subsequent treatment. The findings presented here demonstrate the clinical utility of metabolomic profiling in the diagnosis of ADSL deficiency and highlights the potential of this technology in the diagnostic evaluation of individuals with neurologic phenotypes.

Neuropathological Mechanisms of Seizures in Autism Spectrum Disorder

This manuscript reviews biological abnormalities shared by autism spectrum disorder (ASD) and epilepsy. Two neuropathological findings are shared by ASD and epilepsy: abnormalities in minicolumn architecture and γ-aminobutyric acid (GABA) neurotransmission. The peripheral neuropil, which is the region that contains the inhibition circuits of the minicolumns, has been found to be decreased in the post-mortem ASD brain. ASD and epilepsy are associated with inhibitory GABA neurotransmission abnormalities including reduced GABA_A and GABA_B subunit expression. These abnormalities can elevate the excitation-to-inhibition balance, resulting in hyperexcitablity of the cortex and, in turn, increase the risk of seizures. Medical abnormalities associated with both epilepsy and ASD are discussed. These include specific genetic syndromes, specific metabolic disorders including disorders of energy metabolism and GABA and glutamate neurotransmission, mineral and vitamin deficiencies, heavy metal exposures and immune dysfunction. Many of these medical abnormalities can result in an elevation of the excitatory-to-inhibitory balance. Fragile X is linked to dysfunction of the mGluR5 receptor and Fragile X, Angelman and Rett syndromes are linked to a reduction in GABA_A receptor expression. Defects in energy metabolism can reduce GABA interneuron function. Both pyridoxine dependent seizures and succinic semialdehyde dehydrogenase deficiency cause GABA deficiencies while urea cycle defects and phenylketonuria cause abnormalities in glutamate neurotransmission. Mineral deficiencies can cause glutamate and GABA neurotransmission abnormalities and heavy metals can cause mitochondrial dysfunction which disrupts GABA metabolism. Thus, both ASD and epilepsy are associated with similar abnormalities that may alter the excitatory-to-inhibitory balance of the cortex. These parallels may explain the high prevalence of epilepsy in ASD and the elevated prevalence of ASD features in individuals with epilepsy.

Metabolic and mitochondrial disorders associated with epilepsy in children with autism spectrum disorder

Autism spectrum disorder (ASD) affects a significant number of individuals in the United States, with the prevalence continuing to grow. A significant proportion of individuals with ASD have comorbid medical conditions such as epilepsy. In fact, treatment-resistant epilepsy appears to have a higher prevalence in children with ASD than in children without ASD, suggesting that current antiepileptic treatments may be suboptimal in controlling seizures in many individuals with ASD. Many individuals with ASD also appear to have underlying metabolic conditions. Metabolic conditions such as mitochondrial disease and dysfunction and abnormalities in cerebral folate metabolism may affect a substantial number of children with ASD, while other metabolic conditions that have been associated with ASD such as disorders of creatine, cholesterol, pyridoxine, biotin, carnitine, γ-aminobutyric acid, purine, pyrimidine, and amino acid metabolism and urea cycle disorders have also been associated with ASD without the prevalence clearly known. Interestingly, all of these metabolic conditions have been associated with epilepsy in children with ASD. The identification and treatment of these disorders could improve the underlying metabolic derangements and potentially improve behavior and seizure frequency and/or severity in these individuals. This paper provides an overview of these metabolic disorders in the context of ASD and discusses their characteristics, diagnostic testing, and treatment with concentration on mitochondrial disorders. To this end, this paper aims to help optimize the diagnosis and treatment of children with ASD and epilepsy. This article is part of a Special Issue entitled "Autism and Epilepsy".

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.

Syndromes at risk of status epilepticus in children: genetic and pathophysiological issues

Status epilepticus (SE) is a medical emergency with increased risk of morbidity and mortality in all age groups. Recent research has identified a variety of new genes implicated in disorders with severe epilepsies as a prominent feature. Autoimmune mechanisms have also been recently recognised as a cause of epilepsies with SE as a characteristic symptom. Knowledge about the aetiology potentially underlying SE may help to guide diagnostics and eventually influence treatment decisions. This review recapitulates, in brief, the risk of SE in specific clinical settings, provides an overview of paediatric epilepsy syndromes more commonly, or by definition, associated with SE, and summarizes some recent research data on genetic defects and disease mechanisms implicated in the pathogenesis of epilepsies frequently accompanied by SE.

Inborn errors of purine metabolism: clinical update and therapies

Inborn errors of purine metabolism exhibit broad neurological, immunological, haematological and renal manifestations. Limited awareness of the phenotypic spectrum, the recent descriptions of newer disorders and considerable genetic heterogeneity, have contributed to long diagnostic odysseys for affected individuals. These enzymes are widely but not ubiquitously distributed in human tissues and are crucial for synthesis of essential nucleotides, such as ATP, which form the basis of DNA and RNA, oxidative phosphorylation, signal transduction and a range of molecular synthetic processes. Depletion of nucleotides or accumulation of toxic intermediates contributes to the pathogenesis of these disorders. Maintenance of cellular nucleotides depends on the three aspects of metabolism of purines (and related pyrimidines): de novo synthesis, catabolism and recycling of these metabolites. At present, treatments for the clinically significant defects of the purine pathway are restricted: purine 5'-nucleotidase deficiency with uridine; familial juvenile hyperuricaemic nephropathy (FJHN), adenine phosphoribosyl transferase (APRT) deficiency, hypoxanthine phosphoribosyl transferase (HPRT) deficiency and phosphoribosyl-pyrophosphate synthetase superactivity (PRPS) with allopurinol; adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) deficiencies have been treated by bone marrow transplantation (BMT), and ADA deficiency with enzyme replacement with polyethylene glycol (PEG)-ADA, or erythrocyte-encapsulated ADA; myeloadenylate deaminase (MADA) and adenylosuccinate lyase (ADSL) deficiencies have had trials of oral ribose; PRPS, HPRT and adenosine kinase (ADK) deficiencies with S-adenosylmethionine; and molybdenum cofactor deficiency of complementation group A (MOCODA) with cyclic pyranopterin monophosphate (cPMP). In this review we describe the known inborn errors of purine metabolism, their phenotypic presentations, established diagnostic methodology and recognised treatment options.

Inborn errors of pyrimidine metabolism: clinical update and therapy

Inborn errors involving enzymes essential for pyrimidine nucleotide metabolism have provided new insights into their fundamental physiological roles as vital constituents of nucleic acids as well as substrates of lipid and carbohydrate metabolism and in oxidative phosphorylation. Genetic aberrations of pyrimidine pathways lead to diverse clinical manifestations including neurological, immunological, haematological, renal impairments, adverse reactions to analogue therapy and association with malignancies. Maintenance of cellular nucleotides depends on the three aspects of metabolism of pyrimidines: de novo synthesis, catabolism and recycling of these metabolites. Of the ten recognised disorders of pyrimidine metabolism treatment is currently restricted to only two disorders: hereditary orotic aciduria (oral uridine therapy) and mitochondrial neurogastrointestinal encephalomyopathy (MNGIE; allogeneic hematopoetic stem cell transplant and enzyme replacement). The ubiquitous role that pyrimidine metabolism plays in human life highlights the importance of improving diagnostic evaluation in suggestive clinical settings, which will contribute to the elucidation of new defects, future development of novel drugs and therapeutic strategies. Limited awareness of the expanding phenotypic spectrum, with relatively recent descriptions of newer disorders, compounded by considerable genetic heterogeneity has often contributed to the delays in the diagnosis of this group of disorders. The lack of an easily recognisable, easily measurable end product, akin to uric acid in purine metabolism, has contributed to the under-recognition of these disorders.This review describes the currently known inborn errors of pyrimidine metabolism, their variable phenotypic presentations, established diagnostic methodology and recognised treatment options.

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

OBJECTIVES

Adenylosuccinate 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 METHODS

A 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).

RESULTS

Following 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.

CONCLUSIONS

Screening 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.

Inherent properties of adenylosuccinate lyase could explain S-Ado/SAICAr ratio due to homozygous R426H and R303C mutations

Adenylosuccinate lyase (ADSL) is a homotetrameric enzyme involved in the de novo purine biosynthesis pathway and purine nucleotide cycle. Missense mutations in the protein lead to ADSL deficiency, an inborn error of purine metabolism characterized by neurological and physiological symptoms. ADSL deficiency is biochemically diagnosed by elevated levels of succinylaminoimidazolecarboxamide riboside (SAICAr) and succinyladenosine (S-Ado), the dephosphorylated derivatives of the substrates. S-Ado/SAICAr ratios have been associated with three phenotypic groups. Different hypotheses to explain these ratios have been proposed. Recent studies have focused on measuring activity on the substrates independently. However, it is important to examine mixtures of the substrates to determine if mutations affect enzyme activity on both substrates similarly in these conditions. The two substrates may experience an indirect communication due to being acted upon by the same enzyme, altering their activities from the non-competitive case. In this study, we investigate this hidden coupling between the two substrates. We chose two mutations that represent extremes of the phenotype, R426H and R303C. We describe a novel electrochemical-detection method of measuring the kinetic activity of ADSL in solution with its two substrates at varying concentration ratios. Furthermore, we develop an enzyme kinetic model to predict substrate activity from a given ratio of substrate concentrations. Our findings indicate a non-linear dependence of the activities on the substrate ratios due to competitive binding, distinct differences in the behaviors of the different mutations, and S-Ado/SAICAr ratios in patients could be explained by inherent properties of the mutant enzyme.

Genetic and metabolomic analysis of AdeD and AdeI mutants of de novo purine biosynthesis: cellular models of de novo purine biosynthesis deficiency disorders

Purines are molecules essential for many cell processes, including RNA and DNA synthesis, regulation of enzyme activity, protein synthesis and function, energy metabolism and transfer, essential coenzyme function, and cell signaling. Purines are produced via the de novo purine biosynthesis pathway. Mutations in purine biosynthetic genes, for example phosphoribosylaminoimidazole carboxylase/phosphoribosylaminoimidazole succinocarboxamide synthetase (PAICS, E.C. 6.3.2.6/E.C. 4.1.1.21), can lead to developmental anomalies in lower vertebrates. Alterations in PAICS expression in humans have been associated with various types of cancer. Mutations in adenylosuccinate lyase (ADSL, E.C. 4.3.2.2) or 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/IMP cyclohydrolase (ATIC, E.C. 2.1.2.3/E.C. 3.5.4.10) lead to inborn errors of metabolism with a range of clinical symptoms, including developmental delay, severe neurological symptoms, and autistic features. The pathogenetic mechanism is unknown for these conditions, and no effective treatments exist. The study of cells carrying mutations in the various de novo purine biosynthesis pathway genes provides one approach to analysis of purine disorders. Here we report the characterization of AdeD Chinese hamster ovary (CHO) cells, which carry genetic mutations encoding p.E177K and p.W363* variants of PAICS. Both mutations impact PAICS structure and completely abolish its biosynthesis. Additionally, we describe a sensitive and rapid analytical method for detection of purine de novo biosynthesis intermediates based on high performance liquid chromatography with electrochemical detection. Using this technique we detected accumulation of AIR in AdeD cells. In AdeI cells, mutant for the ADSL gene, we detected accumulation of SAICAR and SAMP and, somewhat unexpectedly, accumulation of AIR. This method has great potential for metabolite profiling of de novo purine biosynthesis pathway mutants, identification of novel genetic defects of purine metabolism in humans, and elucidating the regulation of this critical metabolic pathway.

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.

Structural and biochemical characterization of human adenylosuccinate lyase (ADSL) and the R303C ADSL deficiency-associated mutation

Adenylosuccinate lyase (ADSL) deficiency is a rare autosomal recessive disorder, which causes a defect in purine metabolism resulting in neurological and physiological symptoms. ADSL executes two nonsequential steps in the de novo synthesis of AMP: the conversion of phosphoribosylsuccinyl-aminoimidazole carboxamide (SAICAR) to phosphoribosylaminoimidazole carboxamide, which occurs in the de novo synthesis of IMP, and the conversion of adenylosuccinate to AMP, which occurs in the de novo synthesis of AMP and also in the purine nucleotide cycle, using the same active site. Mutation of ADSL's arginine 303 to a cysteine is known to lead to ADSL deficiency. Interestingly, unlike other mutations leading to ADSL deficiency, the R303C mutation has been suggested to more significantly affect the enzyme's ability to catalyze the conversion of succinyladenosine monophosphate than that of SAICAR to their respective products. To better understand the causation of disease due to the R303C mutation, as well as to gain insights into why the R303C mutation potentially has a disproportional decrease in activity toward its substrates, the wild type (WT) and the R303C mutant of ADSL were investigated enzymatically and thermodynamically. Additionally, the X-ray structures of ADSL in its apo form as well as with the R303C mutation were elucidated, providing insight into ADSL's cooperativity. By utilizing this information, a model for the interaction between ADSL and SAICAR is proposed.

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.

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.

Mutations of ATIC and ADSL affect purinosome assembly in cultured skin fibroblasts from patients with AICA-ribosiduria and ADSL deficiency

The purinosome is a multienzyme complex composed by the enzymes active in de novo purine synthesis (DNPS) that cells transiently assemble in their cytosol upon depletion or increased demand of purines. The process of purinosome formation has thus far been demonstrated and studied only in human epithelial cervical cancer cells (HeLa) and human liver carcinoma cells (C3A) transiently expressing recombinant fluorescently labeled DNPS proteins. Using parallel immunolabeling of various DNPS enzymes and confocal fluorescent microscopy, we proved purinosome assembly in HeLa, human hepatocellular liver carcinoma cell line (HepG2), sarcoma osteogenic cells (Saos-2), human embryonic kidney cells (HEK293), human skin fibroblasts (SF) and primary human keratinocytes (KC) cultured in purine-depleted media. Using the identical approach, we proved in cultured skin fibroblasts from patients with AICA-ribosiduria and ADSL deficiency that various mutations of ATIC and ADSL destabilize to various degrees of purinosome assembly and found that the ability to form purinosomes correlates with clinical phenotypes of individual ADSL patients. Our results thus shown that the assembly of functional purinosomes is fully dependent on the presence of structurally unaffected ATIC and ADSL complexes and presumably also on the presence of all the other DNPS proteins. The results also corroborate the hypothesis that the phenotypic severity of ADSL deficiency is mainly determined by structural stability and residual catalytic capacity of the corresponding mutant ADSL protein complexes, as this is prerequisite for the formation and stability of the purinosome and at least partial channeling of succinylaminoimidazolecarboxamide riboside-ADSL enzyme substrates-through the DNPS pathway.

Metabolic and monogenic causes of seizures in neonates and young infants

Seizures in neonates or young infants present a frequent diagnostic challenge. After exclusion of acquired causes, disturbances of the internal homeostasis and brain malformations, the physician must evaluate for inborn errors of metabolism and for other non-malformative genetic disorders as the cause of seizures. The metabolic causes can be categorized into disorders of neurotransmitter metabolism, disorders of energy production, and synthetic or catabolic disorders associated with brain malformation, dysfunction and degeneration. Other genetic conditions involve channelopathies, and disorders resulting in abnormal growth, differentiation and formation of neuronal populations. These conditions are important given their potential for treatment and the risk for recurrence in the family. In this paper, we will succinctly review the metabolic and genetic non-malformative causes of seizures in neonates and infants less than 6 months of age. We will then provide differential diagnostic clues and a practical paradigm for their evaluation.

Novel mutations in xanthine dehydrogenase/oxidase cause severe hypouricemia: biochemical and molecular genetic analysis in two Czech families with xanthinuria type I

BACKGROUND

The article describes the clinical, biochemical, enzymological and molecular genetics findings in two patients from two families with xanthinuria type I.

METHODS

Biochemical analysis using high performance liquid chromatography, allopurinol loading test and analysis of xanthine oxidase activity in plasma and of uromodulin excretion in urine were performed. Sequencing analysis of the xanthine dehydrogenase gene and the haplotype and statistical analyses of consanguinity were performed.

RESULTS

Probands showed extremely low concentrations of uric acid, on seven occasions under the limit of detection. The concentration of uric acid in 38-year-old female was 15 μmol/L in serum and 0.04 mmol/L in urine. Excretion of xanthine in urine was 170 mmol/mol creatinine. The concentration of uric acid in 25-year-old male was 0.03 mmol/L in urine. Excretion of xanthine in urine was 141 mmol/mol creatinine. The allopurinol loading test confirmed xanthinuria type I. The xanthine oxidase activities in patients were 0 and 0.4 pmol/h/mL of plasma. We found three nonsense changes: p.P214QfsX4 and unpublished p.R825X and p.R881X.

CONCLUSIONS

We found two nonconsanguineous compound heterozygotes with xanthinuria type I caused by three nonsense changes. The methods used did not confirm consanguinity in the probands, thus there might be an unconfirmed biological relationship or mutational hotspot.

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.

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).

Adenylosuccinate lyase deficiency in the United Kingdom pediatric population: first three cases

Adenylosuccinate lyase deficiency is an autosomal recessive disorder of purine metabolism resulting from mutations in the ADSL gene on chromosome subband 22q13.1 and associated with a wide range of clinical manifestations. Although there is currently no effective treatment of ADSL deficiency, recognition of the condition is important, because prenatal genetic diagnosis can be offered to affected families. Reported here are the cases of the only three children diagnosed to date in the United Kingdom with adenylosuccinate lyase deficiency, to further delineate the clinical phenotype and to raise awareness of this disorder.

Biochemical and structural analysis of 14 mutant adsl enzyme complexes and correlation to phenotypic heterogeneity of adenylosuccinate lyase deficiency

Adenylosuccinate lyase (ADSL) deficiency is neurometabolic disease characterized by accumulation of dephosphorylated enzyme substrates SAICA-riboside (SAICAr) and succinyladenosine (S-Ado) in body fluids of affected individuals. The phenotypic severity differs considerably among patients: neonatal fatal, severe childhood, and moderate phenotypic forms correlating with different values for the ratio between S-Ado and SAICAr concentrations in cerebrospinal fluid have been distinguished. To reveal the biochemical and structural basis for this phenotypic heterogeneity, we expressed and characterized 19 ADSL mutant proteins identified in 16 patients representing clinically distinct subgroups. Respecting compound heterozygosity and considering the homotetrameric structure of ADSL, we used intersubunit complementation and prepared and characterized genotype-specific heteromeric mutant ADSL complexes. We correlated clinical phenotypes with biochemical properties of the mutant proteins and predicted structural impacts of the mutations. We found that phenotypic severity in ADSL deficiency is correlated with residual enzymatic activity and structural stability of the corresponding mutant ADSL complexes and does not seem to result from genotype-specific disproportional catalytic activities toward one of the enzyme substrates. This suggests that the S-Ado/SAICAr ratio is probably not predictive of phenotype severity; rather, it may be secondary to the degree of the patient's development (i.e., to the age of the patient at the time of sample collection).

In vivo proton MR spectroscopy findings specific for adenylosuccinate lyase deficiency

Adenylosuccinate lyase (ADSL) deficiency is an inherited metabolic disorder affecting predominantly the central nervous system. The disease is characterized by the accumulation of succinylaminoimidazolecarboxamide riboside and succinyladenosine (S-Ado) in tissue and body fluids. Three children presented with muscular hypotonia, psychomotor delay, behavioral abnormalities, and white matter changes on brain MRI. Two of them were affected by seizures. Screening for inborn errors of metabolism including in vitro high resolution proton MRS revealed an ADSL deficiency that was confirmed genetically in all cases. All patients were studied by in vivo proton MRS. In vitro high resolution proton MRS of patient cerebrospinal fluid showed singlet resonances at 8.27 and 8.29 ppm that correspond to accumulated S-Ado. In vivo proton MRS measurements also revealed a prominent signal at 8.3 ppm in gray and white matter brain regions of all patients. The resonance was undetectable in healthy human brain. In vivo proton MRS provides a conclusive finding in ADSL deficiency and represents a reliable noninvasive diagnostic tool for this neurometabolic disorder.

Neonatal Seizures: When to Consider and How to Investigate for an Inborn Error of Metabolism

Seizures occur more frequently in the neonatal period than in the remainder of childhood. Neonatal seizures can have different aetiologies. Inborn errors of metabolism are rare causes of seizures in the newborn. However, they are an important cause of intractable neonatal seizures, accounting for 30% of cases. Diagnosis is necessary for timely institution of appropriate treatment and is important in determining clinical outcome. As these are genetic conditions, it allows for appropriate genetic counselling. We describe the clinical presentation of neonatal seizures and the investigation findings in symptomatic neonatal seizures and epilepsy syndromes that arise in the neonatal period. The approach in diagnosis and investigation of an underlying inborn error of metabolism is described and inborn errors of metabolism that are important causes of neonatal seizures are reviewed.

Inborn errors of purine and pyrimidine metabolism

Genetic disorders of purine and pyrimidine (PP) metabolism are under-reported and infrequently mentioned in the general literature, as well as in reviews dedicated to other inborn errors of metabolism. Owing to limited awareness, relatively recent recognition, as well as considerable phenotypic variation, these disorders may often be misdiagnosed or remain undiagnosed. Disorders that arise as a result of dysfunction in PP metabolism represent some of the most challenging diagnostic problems in medicine. In addition to their low prevalence rates, they also present with extremely variable signs and symptoms. They may affect any system in a variety of manners, and often mimic other, more recognizable disorders. The diagnostic problem is compounded by the fact that some biochemically affected patients are symptom-free. Rapidly evolving laboratory techniques such as high-performance liquid chromatography coupled to tandem mass spectrometry are now well established as the preferred method for detection for these defects, but currently the most important step in diagnosis consists of suspecting the disorder. Diagnosis is vital because genetic counselling can be provided and, in some cases, specific treatment can be offered that may slow or even reverse clinical symptoms. If undiagnosed, these disorders can be devastating to patients and their families, resulting in early death or institutionalization for the rest of patient's life. This article describes the current state of knowledge about inborn errors of purine and pyrimidine metabolism, focusing on the varying clinical presentations, the laboratory findings and discusses indications for selective screening for these disorders.