Inborn Errors of Metabolism PDF

Inborn Errors of Metabolism Prof. Marian Brennan [email protected]  LEARNING OBJECTIVES Describe the classification of IEMs Describe newborn screening to detect inborn errors Discuss disorders of amino acid metabolism – Phenylketonuria, tyrosinaemia, organic aciduria, alkaptonuria, maple...

Inborn Errors of Metabolism Prof. Marian Brennan [email protected]  LEARNING OBJECTIVES Describe the classification of IEMs Describe newborn screening to detect inborn errors Discuss disorders of amino acid metabolism – Phenylketonuria, tyrosinaemia, organic aciduria, alkaptonuria, maple syrup urine disease Discuss disorders of lipid metabolism (MCAD) Outline disorders involving complex molecules including lysosomal storage disorders, peroxisomal disorders and congenital disorders of glycosylation Discuss disorders of energy metabolism and mitochondrial disorders Discuss disorders of gluconeogenesis Discuss disorders of carbohydrate metabolism (galactosemia, hereditary fructose intolerance and fructosuria)  INBORN ERRORS OF METABOLISM (IEMS) Genetic disorders of metabolism, mostly involving single genes which code for enzymes involved in metabolic pathways or transport proteins Clinical presentation usually arise due to: accumulation of toxic substances which interfere with normal function deficiency of product of a metabolic pathway IMPAIRED ENZYME ACTIVITY deficiency of product X Deficiency of product SUBSTRATE BUILD-UP Accumulation of substrate Accumulation of substrate SUBSTRATE BUILD-UP toalternateproduct conversion conversion to alternate product INBORN ERRORS OF METABOLISM Individually rare but collectively common Presentation at any age, neonate into adulthood Diagnosis does not necessarily require extensive knowledge of biochemical pathways or individual metabolic diseases understanding of broad clinical manifestations of IEMs provides basis for knowing when to consider diagnosis high index of suspicion most important in making diagnosis Emergency treatment Requires prompt therapy, aimed at metabolic stabilization  Age of onset of IEMs Age at clinical presentation varies for individual IEM & variants Timing of presentation depends on: X The level of accumulation of toxic metabolites deficiency of product Onset and severity can be exacerbated by: diet intercurrent illness  Presentation of IEMs Disorders of carbohydrate or protein metabolism and energy production tend to: present in neonatal period or early infancy to be unrelenting and rapidly progressive less severe variants usually present later Fatty acid oxidation, glycogen storage, and lysosomal storage disorders tend to: present in infancy or childhood with subtle neurological or psychiatric features often undiagnosed until adulthood Rationale for Newborn Screening SE iii theirheel Heel prick test @ 3-5 days old Allows for early detection, before clinical signs or symptoms. Early diagnosis allows for the early treatment => better clinical outcomes Reduces morbidity or premature mortality  NEWBORN SCREENING IN IRELAND Disorders of carbohydrate Galactosaemia metabolism Phenylketonuria (PKU) Amino acid Maple syrup urine disease (MSUD) disorders Homocystinuria Disorders of Medium Chain Acyl CoA Dehydrogenase deficiency fatty acid (MCADD) oxidation Organic Glutaric aciduria type 1 (GA1) aciduria’s Also screen for cystic fibrosis and congenital hypothyroidism – not IEMs  Classification of inborn errors of metabolis Group 1 Disorders thatcauseintoxication leadstoprogressive of toxic accumulation e.gPKU compound Group2 Disordersofenergy metabolism IEMof intermediary metabolis mitochondrialdefects eg Classification of IEMs Group3 Disordersinvolvingcomplexmolecules involvescellularorganelles e lysosomalstoragedisorders Group 1: disorders lead to progressive accumulation of toxic compound causing intoxication e.g. PKU, MSUD, Organic acidurias Group 2: disorders IEM of intermediary metabolism, symptoms due in part to of energy energy deficiency metabolism (Mitochondrial or cytoplasmic energy defects) Group 3: disorders Involves cellular organelles including diseases associated with disturbed synthesis or catabolism of complex molecules involving complex e.g. Lysosomal storage disorders, peroxisomal disorders & intracellular molecules trafficking disorders Jean-Marie Saudubray  Group 1: Disorders which give rise to intoxication Share clinical similarities: Do not interfere with embryo-foetal development Present after a symptom-free interval Clinical signs of intoxication may be: Acute – vomiting, coma, liver failure Chronic – failure to thrive, developmental delay, ectopic lentis (dislocation of lens) Most are treatable with removal of toxin Group 1: Disorders which give rise to intoxication Amino acidopathies: Phenylketonuria, Maple Syrup Urine Disease, Homocystinuria, Tyrosinaemias Organic acidurias: Methylmalonic aciduria, Propionic aciduria, Glutaric aciduria Type l Urea cycle disorders Ornithine TransCarbamylase (OTC) deficiency, Citrullinaemia Sugar intolerances Classical Galactosaemia, Hereditary Fructose Intolerance Metal intoxication Wilson’s disease, Menkes disease, Haemochromatosis Porphyrias  Hyperphenylalaninaemia- (Phenylketonuria – PKU) Autosomal recessive Incidence: ~ 97% due to phenylalanine hydroxylase enzyme defect ~ 3% due to defective synthesis of the cofactor, tetrahydrobiopterin Diagnosis: – Newborn screen (Heel-prick) test – Biochemical – amino acid analysis Clinical symptoms, if not detected: – irritability, vomiting, seizures – irreversible brain damage by 4 - 6 months – reduced melanin production pale skin, fair hair, blue eyes – frequently generalised eczema Management: – Diet low in Phenylalanine; supplemented with Tyrosine – Cofactor related form Neurotransmitter supplementation  Hyperphenylalaninaemia - (Phenylketonuria – PKU) Phenylalanine hydroxylase Phenylalanine X Tyrosine BH4 BH2 NAD NADH + H+ Dihydropteridin reductase Phenylketones in urine Please review associated online case study on Moodle BH4 = tetrahydrobiopterin In Phenylketonuria (PKU), the enzyme phenylalanine hydroxylase is deficient. This prevents phenylalanine from converting into tyrosine, leading to the buildup of phenylalanine and production of phenylketones (detected in urine). The cofactor tetrahydrobiopterin (BH₄) and the enzyme dihydropteridine reductase are involved in this pathway.  Metabolism of Phenylalanine & Tyrosine PHENYLALANINE Albinism PKU Phenylalanine hydroxylase (PAH) TYROSINE MELANIN Tyrosinaemia Type II Tyrosine aminotransferase 4-HYDROXYPHENYLPYRUVIC ACID 4-hydroxyphenylpyruvic acid oxidase Tyrosinaemia Type III HOMOGENTISIC ACID Homogentisic acid oxidase Alkaptonuria MALEYLACETOACETIC ACID Tyrosinaemia Type Ib Maleylacetoacetate isomerase FUMARYLACETOACETIC ACID Tyrosinaemia Type I Fumarylacetoacetate hydrolase FUMARATE + ACETOACETATE CO2 + H2O Phenylalanine is normally converted to tyrosine via phenylalanine hydroxylase. Tyrosine undergoes further metabolism into melanin or breaks down into intermediate compounds leading to fumarate and acetoacetate for energy. Disorders like Tyrosinaemia and Alkaptonuria result from enzyme deficiencies at different stages of tyrosine breakdown. Example: Alkaptonuria is due to a defect in homogentisic acid oxidase, leading to a buildup of homogentisic acid. Tyrosinaemia type I Defect: Deficiency in fumarylacetoacetate hydrolase Biochemistry: Accumulation of fumaryl acetoacetate and its metabolites in the urine particularly succinyl acetone Symptoms: Characteristic cabbage like odor Liver failure and renal tubular acidosis Treatment: dietary restriction of Phe and Tyr Drug - nitisinone  Treatment of Tyrosinaemia type I Albinism PHENYLALANINE Phenylalanine hydroxylase TYROSINE Tyrosine aminotransferase 4-HYDROXYPHENYLPYRUVIC ACID Nitisinone X 4-hydroxyphenylpyruvic acid oxidase NTBC HOMOGENTISIC ACID Homogentisic acid oxidase MALEYLACETOACETIC ACID Maleylacetoacetate isomerase FUMARYLACETOACETIC ACID SUCCINYLACETONE Tyrosinaemia Type l Fumarylacetoacetate hydrolase FUMARATE + ACETOACETATE CO2 + H2O You don’t need to know the structure of nitisinone Biochemical defect in Alkaptonuria Albinism PHENYLALANINE Phenylalanine hydroxylase TYROSINE MELANIN Tyrosine aminotransferase 4-HYDROXYPHENYLPYRUVIC ACID 4-hydroxyphenylpyruvic acid oxidase HOMOGENTISIC ACID X Alkaptonuria Homogentisic acid oxidase MALEYLACETOACETIC ACID Maleylacetoacetate isomerase FUMARYLACETOACETIC ACID Fumarylacetoacetate hydrolase FUMARATE + ACETOACETATE CO2 + H2O ALKAPTONURIA - CLINICAL MANIFESTATIONS Dark urine Pigmentation phenotype called 15 min 2 hrs ochronosis – pigmentation of ears and eyes Arthritis associated with calcification of joints  Maple syrup urine Disease (branched-chain ketoacid dehydrogenase deficiency) Defect: metabolism of leucine, isoleucine & valine. (deficiency in α-keto acid dehydrogenase) Biochemistry: α-amino acids and their α-keto analogs (elevated in plasma & urine) Symptoms: normal first few days of life progressive lethargy, weight loss, episodes of hypertonia & hypotonia. Maple syrup odour to the urine. Ketosis, coma and death if not treated. Treatment: Dietary restriction of branched chain amino acids Case study A 5-year-old is brought to her pediatrician because her mother notices that she is having difficulty with her sight. Her mother explains that she has had slow mental and physical development compared to her peers. The girl has long ”spidery” fingers and is tall for her age. She has a downward dislocation of her lens in one of her eyes. Laboratory tests reveal that she has elevated levels of methionine. She also has elevated levels of homocysteine in her urine.  Homocystinuria Defect in cystathionine synthase Accumulation of homocysteine in the urine Methionine and metabolites elevated in the blood Cardiovascular disease, deep vein thrombosis, thromboembolism & stroke, brain damage, osteoporosis, dislocation of the lens  Organic Aciduria Some IEMs “giving rise to intoxication” can be classified as organic aciduria’s Causes accumulation of organic acids in blood and urine. Autosomal recessive Organic acids: include carboxylic acids, with or without keto, hydroxyl or other non-amino functional groups common features – water soluble, acids and ninhydrin stain negative (No N group) Derived from dietary protein, fat and carbohydrate https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3210240/  GLUTARIC ACIDURIA TYPE I (GA1) Defect: metabolism of lysine, hydroxylysine & tryptophan (defieciency in glutaryl CoA dehydrogenase) Biochemistry: harmful organic acids accumulate Symptoms: Dystonia, dyskinesia, excretion of glutaric and 3 hydroxy glutaric acids in urine, neuronal degeneration, seizures untreated => brain damage & possibly death Treatment: Dietary restriction of protein supplementation with carnitine  Group 2: disorders involved in energy metabolism Diagnosis often difficult Common symptoms include: Hypoglycaemia, lactic acidaemia, hepatomegaly, severe hypotonia, myopathy, cardiomyopathy, sudden unexpected death (SIDs) Mitochondrial defects: Congenital lactic acidaemias: – Pyruvate dehydrogenase deficiency – Pyruvate carboxylase deficiency – TCA cycle enzyme deficiencies Respiratory chain disorders Fatty Acid Oxidation and ketone body disorder Some mitochondrial disorders may interfere with embryo-foetal development Cytoplasmic defects: Glycolysis, Gluconeogenesis and Glycogen metabolism  Medium-chain acyl-coenzyme A dehydrogenase deficiency (MCADD) Disorder of fatty acid oxidation due to impaired break down medium-chain fatty acids into acetyl-CoA. Symptoms: hypoketotic hypoglycemia, liver dysfunction, SID, lethargy, seizures and coma. Intolerance to fasting MCAD is responsible for the dehydrogenation step of fatty acids with chain lengths between 6 and 12 carbons as they undergo beta-oxidation in the mitochondria. Beta-oxidation of long chain fatty acids produces two carbon units, acetyl- CoA and the reducing equivalents NADH and FADH2. Energy from fatty acid oxidation  Medium-chain fatty acyl-coA dehydrogenase deficiency (MCADD) X Defect in the acyl-coA dehydrogenase prevents FADH2 formation Prevents formation of subsequent reactions therefore Prevents formation of NADH+ H+ And Actyl CoA è Huge loss of energy production Chapter 16 Lippincott’s Biochemistry Gluconeogenesis Synthesis of glucose Substrates: Lactate (from anaerobic glycolysis) Glycerol(from hydrolysis of triacylglycerols in fasting state) Amino acids Specific enzymes are required to by-pass the 3 irreversible reactions in glycolysis  Disorders of gluconeogenesis associated with hypoglycaemia Pyruvate carboxylase deficiency Presentation Severe neonatal - seizures, coma, lactic acidosis, mild hypoglycaemia, Mild infantile – psychomotor impairment, mild lactic acidosis Diagnosis ↑ lactate, ketosis Fructose-1,6-bisphosphatase deficiency Presentation Acute onset with hepatomegaly, Hypoglycaemia, seizures, coma Diagnosis ↑ lactate, ketosis PEP carboxykinase deficiency Extremely rare  Mitochondrial disease Maternal inheritance Only egg cells contribute mitochondria to developing embryo Ø Only mothers pass on mitochondrial conditions to off-spring Øif mother has mitochondrial condition, ALL offspring inherit it. Øif father has mitochondrial condition, NO offspring inherit it. Both sexes affected Transmission only by females Phenotype of affected individual varies significantly depending of plasmy  Plasmy Hundreds of mtDNA copies in every eukaryotic cell Homoplasmy all copies of mtDNA identical IEM displaying homoplasmy: presence of a mutation affecting all mtDNA copies Heteroplasmy presence of mixture of more than one type of mtDNA most mtDNA mutations heteroplasmic Mutations only occurring in some copies of mtDNA Number of mutated mtDNA molecules inherited by offspring can vary: Ø twin births, one baby may receive more than half mutant mtDNA molecules while other twin may receive only tiny fraction of mutant mtDNA and thus not present clinically symptoms of severe heteroplasmic mitochondrial disorders frequently do not appear until adulthood as many cell divisions required for cell to receive enough mitochondria containing mutant alleles to cause symptoms. Clinical presentation – phenotype depends on mutation load within cell of specific tissue/organ  Mitochondrial disorders Disorders of enzymes or enzyme complexes involved in generation of chemical energy by Oxidative Phosphorylation Mitochondrial Disorders include: Pyruvate dehydrogenase (PDH) complex TCA cycle Electron transport chain (ETC) ATP synthase Blockage of ETC due to O2 deficiency, genetic defects or inhibitors causes rise in NADH+/NAD ratio and inhibits PDH and TCA MITOCHONDRIAL DISEASES DIAGNOSTIC CRITERIA Type of inheritance Clinical symptoms – encephalopathies – myopathies – cardiomyopathies Biochemical features Image of ragged red fibers. By Nephron - Own work, CC BY-SA 3.0, – Lactic acidosis https://commons.wikimedia.org/w/index.php?curid=12433248 Lactate often elevated in both blood and CSF Respiratory chain deficiency diagnosis – Enzyme activity of a specific ETC complex often decreased – Morphological features include ragged red fibers (RRF) in muscle biopsy – DNA analysis  CASE: A ‘Three Parent Baby’ 2 siblings died at 6 and 8 months due to a genetic defect in the mtDNA Diagnosed with Leigh syndrome:- failure to thrive, progressive neuropoathy, muscle weakness, psychomotor regression. Children usually die within 2-3 years of respiratory failure. Caused by defects in ETC proteins and some pyruvate dehydrogenase. Maternal nucleus was removed from her egg and inserted into a donor egg that had had its nucleus removed. This was then fertilized with the fathers sperm. Using this procedure, some mitrochondria can be transferred with the nuclear transfer. Reardon S. Nature. 2017 Apr 3;544(7648):17-18 Genetic details of controversial 'three-parent baby' revealed. Pyruvate Dehydrogenase complex (PDH) PDH Pyruvate dehydrogenase deficiency Presentation: Progressive encephalopathy, brain malformation, psychomotor impairment, muscular hypotonia, epilepsy Diagnosis: Increased plasma lactate & enzyme analysis Fibroblasts and muscle  Mitochondrial Respiratory Chain Multiple polypeptide chains for each complex Gene expression mitochondrial and nuclear No. of No. of No. of Subunits Mitochondrial Nuclear Genes Genes Complex I 41 7 34 Complex ll 4 0 4 Complex lll 11 1 10 Complex lV 13 3 10 Complex V 14 2 12 13 70  STORAGE DISORDERS 03/10/2022, 11:56 Word Art Genetic diseases characterised by abnormal accumulation of lipids or carbohydrates Glycogen Storage Disorders (GSDs) - abnormal synthesis or degradation of glycogen - due to a defect in the genes coding for enzymes involved in glycogen metabolism GSDs affect liver & muscle disease presentation & severity depend on the role played by the enzyme & its tissue-specificity Signs: - Hypoglycaemia - Muscle pain / cramps / weakness Glycogen storage disorder will be covered in detail later in your course about:blank 1/1  Group 3: disorders involving complex molecules Symptoms: Permanent, progressive, independent of intercurrent events, unrelated to food intake Treatment: Limited to enzyme replacement or bone marrow transplant. Disorders: Lysosomal storage disorders Sphingolipidoses – Gaucher’s disease, Niemann-Pick disease, Tay-Sachs disease, Krabbe’s disease, Metachromatic leukodystrophy, Fabry’s disease. Mucopolysaccharidosis (glycosaminoglycans) – Hurler’s disease, Hunter’s disease Peroxisomal disorders Zellweger Syndrome, X linked-adrenoleucodystrophy Congenital disorders of glycosylation  Classification of IEMs Group 1: disorders lead to progressive accumulation of toxic compound causing intoxication e.g. PKU, MSUD, Organic acidurias Group 2: disorders IEM of intermediary metabolism, symptoms due in part to of energy energy deficiency metabolism (Mitochondrial or cytoplasmic energy defects) Group 3: disorders Involves cellular organelles including diseases associated with disturbed synthesis or catabolism of complex molecules involving complex e.g. Lysosomal storage disorders, peroxisomal disorders & intracellular molecules trafficking disorders Jean-Marie Saudubray ? ?  Self-directed learning for completion Core concepts video on metabolism and associated questions: https://vle.rcsi.com/mod/page/view.php?id=421572 McGraw-Hill Biochemistry case 38: https://vle.rcsi.com/mod/sharedcourse/view.php?id=421578 Video-Disorders of Carbohydrate metabolism and associated questions: https://vle.rcsi.com/mod/lti/view.php?id=421581 https://vle.rcsi.com/mod/quiz/view.php?id=421582  References Lippincott’s Biochemistry 5th Edition Chapter 8 Chapter 9 Chapter 10 Chapter 11 Chapter 16 Chapter 17 Chapter 19