Diagnosis of Adenylosuccinate Lyase Deficiency by Metabolomic Profiling in Plasma Reveals a Phenotypic Spectrum
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Molecular Genetics and Metabolism Reports 8 (2016) 61–66 Contents lists available at ScienceDirect Molecular Genetics and Metabolism Reports journal homepage: www.elsevier.com/locate/ymgmr Diagnosis of adenylosuccinate lyase deficiency by metabolomic profiling in plasma reveals a phenotypic spectrum Taraka R. Donti a, Gerarda Cappuccio a,b, Leroy Hubert a, Juanita Neira a, Paldeep S. Atwal a,MarcusJ.Millera, Aaron L. Cardon c, V. Reid Sutton a, Brenda E. Porter d, Fiona M. Baumer d, Michael F. Wangler a, Qin Sun a, Lisa T. Emrick a,c, Sarah H. Elsea a,⁎ a Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States b Department of Translational Medical Sciences, Section of Pediatrics, Federico II University, Naples, Italy c Section of Pediatric Neurology and Neuroscience, Baylor College of Medicine, Houston, TX, United States d Stanford Medical School, Stanford, CA, United States article info abstract Article history: Adenylosuccinate lyase (ADSL) deficiency is a rare autosomal recessive neurometabolic disorder that presents Received 28 June 2016 with a broad-spectrum of neurological and physiological symptoms. The ADSL gene produces an enzyme with Received in revised form 20 July 2016 binary molecular roles in de novo purine synthesis and purine nucleotide recycling. The biochemical phenotype Accepted 20 July 2016 of ADSL deficiency, accumulation of SAICAr and succinyladenosine (S-Ado) in biofluids of affected individuals, Available online xxxx 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 Keywords: fi Metabolomic profiling method, untargeted metabolomic pro ling, an analytical scheme capable of generating semi-quantitative z-score ADSL deficiency values for over 1000 unique compounds in a single analysis of a specimen. Using this method to analyze plasma, Intellectual disability we diagnosed ADSL deficiency in four patients and confirmed these findings with targeted quantitative biochem- Succinyladenosine ical 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 subse- quent treatment. The findings presented here demonstrate the clinical utility of metabolomic profiling in the di- agnosis of ADSL deficiency and highlights the potential of this technology in the diagnostic evaluation of individuals with neurologic phenotypes. © 2016 Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 1. Introduction The clinical presentation typically includes intellectual disability, sei- zures, microcephaly, autism spectrum disorder, and respiratory failure. Undifferentiated (non-specific) phenotypes such as non-syndromic Three different forms have been recognized defined by the age of intellectual disability and seizures, pose a challenge to clinicians as the onset and the progression of symptoms: the fatal neonatal form, the se- differential diagnosis is very broad and comprehensive biochemical vere form or type I presenting within the first months of life character- testing for these disorders requires many different tests done on various ized by a severe clinical course, and type II, which is the mild/moderate fluid types. Standard biochemical and molecular studies are often not form presenting within the first years of life with hypotonia and devel- revealing in these cases, often leading to diagnostic odysseys for the pa- opmental delay [1]. Approximately 80 individuals have been reported in tients and families. Adenylosuccinate lyase (ADSL) deficiency (OMIM: the literature, with 5–10% of cases being the fatal neonatal form, 70–80% 103050) is a rare, autosomal recessive inborn error of metabolism of cases being the severe form or type I and 15–20% of type II form. The (IEM) that may present with a wide range of neurological symptoms. overall incidence is unclear [1]. ADSL (EC 4.3.2.2) exists as a homotetramer and catalyzes two path- ways of purine nucleotide metabolism: de novo purine synthesis and the Abbreviations: AICAR, aminoimidazole carboxamide ribotide; ADSL, adenylosuccinate purine nucleotide cycle [1] (Fig. 1). In the de novo pathway, ADSL cata- SM lyase; IEM, inborn errors of metabolism; Global MAPS , Global Metabolomic Assisted lyzes the conversion of succinylaminoimidazole carboxamide ribotide Pathway Screen; SAICAR, succinylaminoimidazole carboxamide ribotide. (SAICAR) into aminoimidazole carboxamide ribotide (AICAR) (Fig. 1). ⁎ Corresponding author at: Department of Molecular and Human Genetics, One Baylor Plaza, NAB2015, Baylor College of Medicine, Houston, TX 77030, United States. In the purine nucleotide cycle, ADSL catalyzes the formation of adenyl- E-mail address: [email protected] (S.H. Elsea). ate (AMP) from adenylosuccinate (S-AMP) during the conversion of http://dx.doi.org/10.1016/j.ymgmr.2016.07.007 2214-4269/© 2016 Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 62 T.R. Donti et al. / Molecular Genetics and Metabolism Reports 8 (2016) 61–66 Fig. 1. Adenylosuccinate lyase and purine nucleotide metabolism. Adenylosuccinate lyase catalyzes two pathways of purine nucleotide metabolism: de novo purine synthesis and the purine nucleotide cycle. Deficiency of ADSL results in blocks in these pathways, causing an increase in SAICAr, as well as an increase in S-Ado, as indicated by the red arrows. Abbreviations are as follows: PRPP, phosphoribosylpyrophosphate; SAICAR, succinylaminoimidazole carboxamide ribotide; SAICAr, succinylaminoimidazole carboxamide riboside; AICAR, aminoimidazole carbozamide ribotide; FAICAR, formyloaminoimidazole carboxamide ribotide; IMP, inosine monophosphate; S-AMP, adenylosuccinate; S-Ado, succinyladenosine; AMP, adenine monophosphate; XMP, xanthine monophosphate; GMP, guanine monophosphate; ADSL, adenylosuccinate lyase; AICAR TF, aminoimidazole carboxamide riboside transformylase; IMP CH, inosine monophosphate cyclohydrolase. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) inosine monophosphate (IMP) into adenine nucleotides (Fig. 1). Bio- contains entries for ~2500 unique human metabolites. Semi- quantita- chemically, ADSL deficiency can be identified by the presence of SAICAr tive analysis was achieved by comparing patient samples to a set of in- and succinyladenosine (S-Ado) in biologic fluids [2], which are other- variant anchor specimen included in each batch. Raw spectral intensity wise not detected or not elevated [3]. values were normalized to the anchor samples, log transformed, and Here, we report four patients with ADSL deficiency of which three compared to a normal reference population to generate z-score values. were identified through untargeted metabolomic profiling of plasma and confirmed by targeted quantitative urine purine analysis and 2.2. Urine purine analysis targeted molecular testing. Global metabolomic profiling is a semi- quantitative tandem mass spectrometry-based technique utilized in The enzymatic synthesis of succinyladenosine and determination of clinical screening for inborn errors of metabolism [4]. purine metabolites by LC-MS/MS were performed as previously de- scribed [8].Briefly, the assay separation was performed on an Acquity 2. Methods UPLC BEH C18 column (1.7 μM IVD 2.1 * 500, Waters Corporation, Mil- ford, USA). The gradient elution was performed with 0.1% formic acid/ 2.1. Untargeted metabolomic profiling 2 mM ammonium acetate (buffer A) and 0.1% formic acid/2 mM ammo- nium acetate in methanol (buffer B). The gradient profile began with Metabolomic profiling (Global MAPS®) was performed by Baylor 100% buffer A, followed by a linear increase to 40% buffer B over Miraca Genetics Laboratories (Houston, TX) and Metabolon, Inc. (Dur- 1.5 min and an increase to 100% buffer B at 1.8 min. The column was ham, NC), as described previously [4–6] with few modifications [7]. then regenerated with 100% buffer A for another 2.5 min. The flow 15 Small molecules were extracted in an 80% methanol solution and sub- rate was 0.5 mL/min. A mixture of N2-adenine (Sigma #644331), 13 13 15 jected to four analyses: two LC-MS/MS analyses in positive mode and C5-adenosine (CIL #CLM3678–0.05), C10, N5-guanosine (CIL 15 15 two LC-MS/MS analyses in negative mode. All chromatographic separa- #CLM-3808-LAS-5), 1,3- N2–xanthine (CIL #NLM-1698) and U- N5- tions were completed using an ACQUITY UPLC (Waters) equipped with deoxyadenosine (CIL #NLM-3895) were used as internal standards. either a Waters BEH C18 column or a Waters BEH Amide column, de- The detection of the analytes was carried out using an Acquity TQ tan- pending on the method, followed by analysis with an Q-Exactive high dem MS (Waters) in the multiple reaction monitoring mode. resolution mass spectrometer (Thermo-Finnigan) [5,7]. Metabolites were identified with known chemical structure by matching the ion 2.3. Molecular analysis chromatographic retention index, nominal mass, and mass spectral fragmentation signatures with reference library entries created from 2.3.1. ADSL sequence analysis authentic standard