Verena Peters

Physician’s guide to the diagnosis, treatment, and follow-up of inherited metabolic diseases

Introductory Chapters.- Amino acids.- Organic acids.- Vitamins and neurotransmitter.- Energy metabolism.- Organelles.- Selected disorder.- Biochemical phenotypes of questionable clinical significance.- Profiles.

Qualitative urinary organic acid analysis: Methodological approaches and performance

SummaryA programme for proficiency testing of biochemical genetics laboratories undertaking urinary qualitative organic acid analysis and its results for 50 samples examined for factors contributing to poor performance are described. Urine samples from patients in whom inherited metabolic disorders have been confirmed as well as control urines were circulated to participants and the results from 94 laboratories were evaluated. Laboratories showed variability both in terms of their individual performance and on a disease-specific basis. In general, conditions including methylmalonic aciduria, propionic aciduria, isovaleric aciduria, mevalonic aciduria, Canavan disease and 3-methylcrotonyl-CoA carboxylase were readily identified. Detection was poorer for other diseases such as glutaric aciduria type II, glyceric aciduria and, in one sample, 3-methylcrotonyl-CoA carboxylase deficiency. To identify the factors that allow some laboratories to perform well on a consistent basis while others perform badly, we devised a questionnaire and compared the responses with the results for performance in the scheme. A trend towards better performance could be demonstrated for those laboratories that regularly use internal quality control (QC) samples in their sample preparation (p = 0.079) and those that participate in further external quality assurance (EQA) schemes (p = 0,040). Clinicians who depend upon these diagnostic services to identify patients with these defects and the laboratories that provide them should be aware of the potential for missed diagnoses and the factors that may lead to improved performance.

JIMD Reports, Volume 24

ACAD9 (acyl-CoA dehydrogenase 9) is an essential factor for the mitochondrial respiratory chain complex I assembly. ACAD9, a member of acyl-CoA dehydrogenase family, has high homology with VLCAD (very long-chain acyl-CoA dehydrogenase) and harbors a homodimer structure. Recently, patients with ACAD9 deficiency have been described with a wide clinical spectrum ranging from severe lethal form to moderate form with exercise intolerance. We report here a prenatal presentation with intrauterine growth retardation and cardiomegaly, with a fatal outcome shortly after birth. Compound heterozygous mutations, a splice-site mutation – c.1030-1G>T and a missense mutation – c.1249C>T; p.Arg417Cys, were identified in the ACAD9 gene. Their effect on protein structure and expression level was investigated. Protein modeling suggested a functional effect of the c.1030-1G>T mutation generating a non-degraded truncated protein and the p. Arg417Cys, creating an aberrant dimer. Our results underscore the crucial role of ACAD9 protein for cardiac function.

Erratum: Leigh-Like Syndrome Due to Homoplasmic m.8993T>G Variant with Hypocitrullinemia and Unusual Biochemical Features Suggestive of Multiple Carboxylase Deficiency (MCD)

Leigh syndrome (LS), or subacute necrotizing encephalomyelopathy, is a genetically heterogeneous, relentlessly progressive, devastating neurodegenerative disorder that usually presents in infancy or early childhood. A diagnosis of Leigh-like syndrome may be considered in individuals who do not fulfil the stringent diagnostic criteria but have features resembling Leigh syndrome. We describe a unique presentation of Leigh-like syndrome in a 3-year-old boy with elevated 3-hydroxyisovalerylcarnitine (C5-OH) on newborn screening (NBS). Subsequent persistent plasma elevations of C5-OH and propionylcarnitine (C3) as well as fluctuating urinary markers were suggestive of multiple carboxylase deficiency (MCD). Normal enzymology and mutational analysis of genes encoding holocarboxylase synthetase (HLCS) and biotinidase (BTD) excluded MCD. Biotin uptake studies were normal excluding biotin transporter deficiency. His clinical features at 13 months of age comprised psychomotor delay, central hypotonia, myopathy, failure to thrive, hypocitrullinemia, recurrent episodes of decompensation with metabolic keto-lactic acidosis and an episode of hyperammonemia. Biotin treatment from 13 months of age was associated with increased patient activity, alertness, Communicated by: Bridget Wilcken The original version of this chapter was revised. An erratum to this chapter can be found at DOI 10.1007/8904_2017_587. S. Balasubramaniam Metabolic Unit, Department of Rheumatology and Metabolic Medicine, Princess Margaret Hospital, Perth, WA, Australia S. Balasubramaniam School of Paediatrics and Child Health, University of Western Australia, Perth, WA, Australia S. Balasubramaniam (*) Western Sydney Genetics Program, Children’s Hospital at Westmead, Westmead, NSW, Australia e-mail: saras329@hotmail.com B. Lewis PathWest Laboratories WA, Princess Margaret Hospital, Perth, WA, Australia D.M. Mock Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR, USA H.M. Said Department of Medicine, University of California School of Medicine Irvine, Irvine, CA, USA M. Tarailo-Graovac Centre for Molecular Medicine, Department of Medical Genetics, Child and Family Research Institute, University of British Columbia, Vancouver, BC, Canada A. Mattman Adult Metabolic Diseases Clinic, Division of Endocrinology and Metabolism, Vancouver General Hospital, UBC, Vancouver, BC, Canada C.D. van Karnebeek Centre for Molecular Medicine, Department of Pediatrics, Child and Family Research Institute, University of British Columbia, Vancouver, BC, Canada D.R. Thorburn : J. Christodoulou Murdoch Childrens Research Institute and Victorian Clinical Genetics Services, Royal Children’s Hospital, Melbourne, VIC, Australia D.R. Thorburn : J. Christodoulou Department of Paediatrics, The University of Melbourne, Melbourne, VIC, Australia R.J. Rodenburg Radboud Center for Mitochondrial Medicine, Radboud University Medical Centre, Nijmegen, The Netherlands JIMD Reports DOI 10.1007/8904_2016_559

JIMD Reports, Volume 37

In patients with 3-hydroxy-3-methylglutaryl (HMG)-CoA lyase deficiency (OMIM 246450), five pregnancies have been described worldwide, which were either terminated or resulted in severe metabolic sequelae during pregnancy or delivery. Here, we report on a patient with HMG-CoA lyase deficiency, who underwent two uncomplicated pregnancies. The 19-year-old patient was admitted because of recurrent vomiting and nausea. Diagnostics revealed pregnancy at week 8 of gestation. Metabolic analyses revealed normal lactate and blood glucose levels and normal acid-base status. Urine organic acid analysis showed an elevated excretion of 3-CH3-glutaric acid, 2,3CH3-glutaconic acid, and 3-CH3-3-OH-glutaric acid. Oral treatment with carnitine and glucose wes administered intravenously during the period of nausea and vomiting. After clinical recovery, a diet with 0.89 g/kg of protein/d and 38 kcal/kg body weight/d was given. Meals were taken every 3 h. Additionally, 70 g of starch was given at midnight to maintain normoglycemia at night time. Peripartum, a complete parenteral nutrition, was delivered through a central venous catheter. The patient delivered a healthy male infant by Caesarean section at week 38 of gestation (Apgar 9/10/10) and remained metabolically stable throughout the peripartum period. Postpartum nutrition was gradually changed from parenteral to oral diet. Two years later, the patient became pregnant again and presented with hyperemesis gravidarum. With metabolic monitoring and treatment as before no decompensation occurred. At week 38 of gestation, she delivered a healthy female infant by elective Caesarian section (Apgar 9/10/ 10). This case report describes the metabolic and obstetric management of two pregnancies in a patient with HMGCoA lyase deficiency with favorable outcome without metabolic complications.

JIMD Reports, Volume 36

Classical galactosemia is detected through newborn screening by measuring galactose-1-phosphate uridylyltransferase (GALT) in the USA primarily via the Beutler spot assay. We report on an 18-month-old patient with glucose-6-phosphate dehydrogenase (G6PD) deficiency that was originally diagnosed with classical galactosemia. The patient presented with elevated liver function enzymes and bilirubinemia and was immediately treated with soy-based formula. Confirmatory tests revealed deficiency of the GALT enzyme, however, full-sequencing of GALT was normal, suggestive of a different ideology. The Beutler spot assay uses three other enzymatic steps in addition to GALT. A deficiency in either of these enzymes can result in suspected decreased GALT activity when using the Beutler assay. Congenital Disorders of Glycosylation screening for phosphoglucomutase-1 deficiency was negative. Quantitative analysis of G6PD enzyme in red blood cells showed a severe deficiency and a deletion in G6PD. Soy-formula, the standard treatment for galactosemia, has been reported to trigger hemolysis in G6PD deficient patients. G6PD and phosphoglucomutase-1 deficiencies should be considered when confirmatory tests are negative for pathogenic variants in GALT and galactose-1-phosphate level is normal. Abbreviations 6PGD 6-Phosphogluconate dehydrogenase ALT Alanine transaminase AST Aspartate aminotransferase CBC Complete blood count CDG Congenital disorders of glycosylation dl Deciliter G6PD Glucose-6-phosphate dehydrogenase Gal-1-P Galacose-1-phosphate GALT Galactose-1-phosphate uridylyltransferase Hb Hemoglobin hr Hour IU International unit mmol Micromole mg Milligram ml Milliliter NADP Nicotinamide adenine dinucleotide phosphate NADPH Nicotinamide adenine dinucleotide phosphate NBS Newborn screening PGM1 Phosphoglucomutase-1 U/g Units per gram UDP-glucose Uridine diphosphate glucose

JIMD Reports, Volume 29

The analysis of (6R)-5,6,7,8-tetrahydrobiopterin (BH4) and neopterin in cerebrospinal fluid (CSF) is often used to identify defects in the pterin biosynthetic pathway affecting monoamine metabolism that can lead to pediatric neurotransmitter diseases. Low levels of BH4 and neopterin alone may not be sufficient to determine the defect, and further testing is often required. We have developed a sensitive liquid chromatography tandem mass spectrometry (LC-MS/MS) method for determination of BH4, 7,8dihydrobiopterin (BH2), neopterin, and sepiapterin in CSF, which provides a more comprehensive evaluation of the pterin pathway. The method utilizes labeled stable isotopes as internal standards and allows for a fast 10-minute analysis by LC/MS/MS over a linear working range of 3 to 200 nmol/L. Total analytical imprecision is less than 14.4% for all pterin metabolites. Accuracy for BH4 and neopterin was determined by comparing data obtained by an alternative method using HPLC with EC and fluorescence detection. Excellent correlation was demonstrated for BH4 (r 1⁄4 0.9646, 1/slope 1⁄4 0.9397; n 1⁄4 28; concentration range 3 to 63 nmol/L) and neopterin (r 1⁄4 0.9919, 1/slope 1⁄4 0.9539; n 1⁄4 13; concentration range 5 to 240 nmol/L). CSF specimens from patients diagnosed with inborn errors of sepiapterin reductase (SR), 6 -py ruvoy l t e t r ahydrop te r in syn thase (PTPS) , dihydropteridine reductase (DHPR), and guanosine triphosphate cyclohydrolase (GTPCH) have been analyzed, and distinct pterin metabolite patterns were consistent with the initial diagnosis. This method differentiates patients with DHPR and SR deficiency from other pterin defects (GTPCH and PTPS) and will be useful for the diagnosis of specific defects in the pterin biosynthetic pathway.

JIMD Reports, Volume 27

Mutations of FBXL4, which encodes an orphan mitochondrial F-box protein, are a recently identified cause of encephalomyopathic mtDNA depletion. Here, we describe the detailed clinical and biochemical phenotype of a neonate presenting with hyperlactatemia, leukoencephalopathy, arrhythmias, pulmonary hypertension, dysmorphic features, and lymphopenia. Next-generation sequencing in the proband identified a homozygous frameshift, c.1641_1642delTG, in FBXL4, with a surrounding block of SNP marker homozygosity identified by microarray. Muscle biopsy showed a paucity of mitochondria with ultrastructural abnormalities, mitochondrial DNA depletion, and profound deficiency of all respiratory chain complexes. Cell-based mitochondrial phenotyping in fibroblasts showed mitochondrial fragmentation, decreased basal and maximal respiration, absence of ATP-linked respiratory and leak capacity, impaired survival under obligate aerobic respiration, and reduced mitochondrial inner membrane potential, with relative sparing of mitochondrial mass. Cultured fibroblasts from the patient exhibited a more oxidized glutathione ratio, consistent with altered cellular redox poise. High-resolution respirometry of permeabilized muscle fibers showed marked deficiency of oxidative phosphorylation using a variety of mitochondrial energy substrates and inhibitors. This constitutes the fourth and most detailed report of FBXL4 deficiency to date. In light of our patient’s clinical findings and genotype (homozygous frameshift), this phenotype likely represents the severe end of the FBXL4 clinical spectrum.

Georg F. Hoffmann and Nenad Blau (eds): Congenital Neurotransmitter Disorders: A Clinical Approach

Congenital neurotransmitter disorders are a group of rare inborn errors of metabolism leading to severe, progressive, mostly early-onset encephalopathies comprising a very wide spectrum of clinical symptoms. Although specific therapeutic approaches can lead to excellent outcome in some of the disorders and although a lot of progress has recently been made regarding diagnostic and therapeutical options, diagnosis is often delayed for many years. Some patients may even remain undiagnosed. Therefore, especially child and adult neurologists should become familiar with the broad spectrum of monogenic neurometabolic diseases to benefit from new insights on clinical indication and interpretation of specialized CSF investigations and therapeutic approaches. The book on Congenital Neurotransmitter Disorders by Hoffmann and Blau is divided into 12 chapters of which the first gives an overview on characteristic clinical signs and symptoms including helpful practical aspects for diagnostic investigations in blood, urine and CSF. The following chapters provide detailed information and recommendations for the different neurotransmitter disorders in a profound, wellstructured, inventive format. Each description starts with clinical presentation followed by biochemical and genetic findings, pathobiochemical disease mechanisms, therapeutical management, long term outcome and diagnostic pitfalls. All chapters are written by well-known experts for the specific disorders from all over the world. This book is a good overview on clinical characteristics, diagnosis and therapy of congenital neurotransmitter disorders. As an asset, the book follows a very practical characterization of each disorder highlighting the clinical process from symptoms to diagnosis and therapy. In addition to that, the book provides numerous tables summarizing clinical aspects, biochemical markers, disease characteristics and treatment options supported by illustrative schematic figures on biochemical pathways or mechanisms. The book supplies both clinicians and clinical biochemists with profound knowledge and hopefully will help to improve awareness for these disorders.