Inborn error of metabolism
Inborn error of metabolism
Classification & external resources
| A few of the metabolic pathways in a cell. Metabolites are shown as dots and enzyme reactions as lines.
Inborn errors of metabolism comprise a large class of genetic diseases involving disorders of metabolism. The majority are due to defects of single genes that code for enzymes that facilitate conversion of various substances (substrates) into others (products). In most of the disorders, problems arise due to accumulation of substances which are toxic or interfere with normal function, or to the effects of reduced ability to synthesize essential compounds. Inborn errors of metabolism are now often referred to as congenital metabolic diseases or inherited metabolic diseases, and these terms are considered synonymous.
The term inborn error of metabolism was coined by a British physician, Archibald Garrod (1857-1936), in the early 20th century (1908). He is known for the "one gene, one enzyme" hypothesis, which arose from his studies on the nature and inheritance of alkaptonuria. His seminal text, Inborn Errors of Metabolism was published in 1923.
Major categories of inherited metabolic diseases
Traditionally the inherited metabolic diseases were categorized as disorders of carbohydrate metabolism, amino acid metabolism, organic acid metabolism, or lysosomal storage diseases. In recent decades, hundreds of new inherited disorders of metabolism have been discovered and the categories have proliferated. Following are some of the major classes of congenital metabolic diseases, with prominent examples of each class. Many others do not fall into these categories. ICD-10 codes are provided where available.
Manifestations and presentations
Because of the enormous number of these diseases and wide range of systems affected, nearly every "presenting complaint" to a doctor may have a congenital metabolic disease as a possible cause, especially in childhood. The following are examples of potential manifestations affecting each of the major organ systems:
- Growth failure, failure to thrive, weight loss
- Ambiguous genitalia, delayed puberty, precocious puberty
- Developmental delay, seizures, dementia, encephalopathy, stroke
- Deafness, blindness, pain agnosia
- Skin rash, abnormal pigmentation, lack of pigmentation, excessive hair growth, lumps and bumps
- Dental abnormalities
- Immunodeficiency, thrombocytopenia, anemia, enlarged spleen, enlarged lymph nodes
- Many forms of cancer
- Recurrent vomiting, diarrhea, abdominal pain
- Excessive urination, renal failure, dehydration, edema
- Hypotension, heart failure, enlarged heart, hypertension, myocardial infarction
- Hepatomegaly, jaundice, liver failure
- Unusual facial features, congenital malformations
- Excessive breathing (hyperventilation), respiratory failure
- Abnormal behavior, depression, psychosis
- Joint pain, muscle weakness, cramps
- Hypothyroidism, adrenal insufficiency, hypogonadism, diabetes mellitus
Because of the multiplicity of conditions, many different diagnostic tests are used for screening. An abnormal result is often followed by a subsequent "definitive test" to confirm the suspected diagnosis.
Common screening tests used in the last sixty years:
Specific diagnostic tests (or focused screening for a small set of disorders):
Dozens of congenital metabolic diseases are now detectable by newborn screening tests, especially the expanded testing using mass spectrometry. This is an increasingly common way for the diagnosis to be made and sometimes results in earlier treatment and a better outcome.
In the middle of the 20th century the principal treatment for some of the amino acid disorders was restriction of dietary protein and all other care was simply management of complications. In the last two decades, enzyme replacement, gene transfer, and organ transplantation have become available and beneficial for many previously untreatable disorders. Some of the more common or promising are listed.
- Dietary restriction
- E.g., reduction of dietary protein remains a mainstay of treatment for phenylketonuria and other amino acid disorders.
- Dietary supplementation or replacement
- E.g., thiamine supplementation benefits several types of lactic acidosis.
- Intermediary metabolites, compounds, or drugs that facilitate or retard specific metabolic pathways
- Enzyme replacement
- Gene transfer
- Bone marrow or organ transplantation
- Treatment of symptoms and complications
- Prenatal diagnosis and avoidance of pregnancy or abortion of an affected fetus
For clinicians and scientists in the field of inborn errors of metabolism, good resources include books by Scriver
, Blau (diagnosis)
, Blau (treatment)
 and Zschocke
. Other ressources include genetests, orphanet, OMIM, Metab-L,societies such as the SSIEM, the SIMD and links therein. For medical students and clinicians looking for overviews of the field, such reviews can be found on pubmed and in good pediatric textbooks (e.g. articles by Saudubray, Ellaway, Raghuveer or Burton and textbooks by Hay or Behrman).
For patients, their families or other individuals seeking good information and support groups, the National Institutes of Health offers the office of rare diseases, genetics home reference, medlineplus and health information. The National Human Genome Research Institute hosts an information center, a section for patients and the public and additional educational resources. Support groups can be found at NORD, Genetic Alliance and Orphanet. The genetic education center at the KUMC has many more useful links.
Charles Scriver, Beaudet, A.L., Valle, D., Sly, W.S., Vogelstein, B., Childs, B., Kinzler, K.W. (accessed 2007). The Online Metabolic and Molecular Bases of Inherited Disease. New York: McGraw-Hill. -
Summaries of 255 chapters, full text through many universities. There is also the OMMBID blog.
Fernandes, J.; Saudubray, J.M.; van den Berghe, G.; Walter, J.H. (2006). Inborn Metabolic Diseases : Diagnosis and Treatment, 4th, Springer, 561 p.
Clarke, J.T.R. (2005). A Clinical Guide to Inherited Metabolic Diseases, 3rd, Cambridge: Cambridge University Press, 358 p. DOI:10.2277/0521614996. ISBN 978-0521614993.
Blau, N.; Duran, M.; Blaskovics, M.E.; Gibson, K.M. (2002). Physician's Guide to the Laboratory Diagnosis of Metabolic Diseases, 2nd, Springer, 716 p. ISBN 978-3-540-42542-7.
Blau, N; Hoffmann, G.F.; Leonard, J.; Clarke, J.T.R. (2006). Physician's Guide to the Treatment And Follow-up of Metabolic Diseases, 1st, Springer, 416 p. ISBN 3-540-22954-X.
Lyon, G.; Kolodny, E.H.; Pastores, G. (2006). Neurology of Hereditary Molecular & Metabolic Disease of Children, 3rd, McGraw-Hill Professional, 500p.
Nyhan, W.L.; Barshop, B.; Ozand, P.T. (2005). Atlas of Metabolic Diseases, 2nd, Oxford University Press, 800 p.
Hoffmann, G.F; Nyhan, W.L.; Zschocke, J.; Kahler, S.G; Mayatepek, E. (2001). Inherited Metabolic diseases. Lippincott Williams & Wilkins, 448 p.
Zschocke, J; Hoffmann, G.F. (2004). Vademecum Metabolicum, 2nd, Schattauer GmbH, 176 p.
- ^ Saudubray J, Sedel F, Walter J. "Clinical approach to treatable inborn metabolic diseases: an introduction". J Inherit Metab Dis 29 (2-3): 261-74. PMID 16763886.
- ^ Ellaway C, Wilcken B, Christodoulou J (2002). "Clinical approach to inborn errors of metabolism presenting in the newborn period". J Paediatr Child Health 38 (5): 511-7. PMID 12354271.
- ^ Raghuveer T, Garg U, Graf W (2006). "Inborn errors of metabolism in infancy and early childhood: an update". Am Fam Physician 73 (11): 1981-90. PMID 16770930.
- ^ Burton B (1998). "Inborn errors of metabolism in infancy: a guide to diagnosis". Pediatrics 102 (6): E69. PMID 9832597.
Hay, W.H., Jr.; Levin, M.J.; Sondheimer, J.M.; Deterding, R.R. (2006). Current Pediatric Diagnosis and Treatment, 18th ed., McGraw-Hill, 1306 p.
Behrman, R.E.; Kliegman, R.M.; Jenson, H.B. (2004). Nelson Textbook of Pediatrics, 17th ed., Elsevier, 2672 p.
|Metabolic pathology / Inborn error of metabolism (E70-90, 270-279)|
|Amino acid||Aromatic (Phenylketonuria, Alkaptonuria, Ochronosis, Tyrosinemia, Albinism, Histidinemia) - Organic acidemias (Maple syrup urine disease, Propionic acidemia, Methylmalonic acidemia, Isovaleric acidemia, 3-Methylcrotonyl-CoA carboxylase deficiency) - Transport (Cystinuria, Cystinosis, Hartnup disease, Fanconi syndrome, Oculocerebrorenal syndrome) - Sulfur (Homocystinuria, Cystathioninuria) - Urea cycle disorder (N-Acetylglutamate synthase deficiency, Carbamoyl phosphate synthetase I deficiency, Ornithine transcarbamylase deficiency, Citrullinemia, Argininosuccinic aciduria, Hyperammonemia) - Glutaric acidemia type 1 - Hyperprolinemia - Sarcosinemia|
|Carbohydrate||Lactose intolerance - Glycogen storage disease (type I, type II, type III, type IV, type V, type VI, type VII) - fructose metabolism (Fructose intolerance, Fructose bisphosphatase deficiency, Essential fructosuria) - galactose metabolism (Galactosemia, Galactose-1-phosphate uridylyltransferase galactosemia, Galactokinase deficiency) - other intestinal carbohydrate absorption (Glucose-galactose malabsorption, Sucrose intolerance) - pyruvate metabolism and gluconeogenesis (PCD, PDHA) -
Pentosuria - Renal glycosuria|
|Lipid storage||Sphingolipidoses/Gangliosidoses: GM2 gangliosidoses (Sandhoff disease, Tay-Sachs disease) - GM1 gangliosidoses - Mucolipidosis type IV - Gaucher's disease - Niemann-Pick disease - Farber disease - Fabry's disease - Metachromatic leukodystrophy - Krabbe disease|
Neuronal ceroid lipofuscinosis (Batten disease) - Cerebrotendineous xanthomatosis - Cholesteryl ester storage disease (Wolman disease)
|Fatty acid metabolism||Lipoprotein/lipidemias: Hyperlipidemia - Hypercholesterolemia - Familial hypercholesterolemia - Xanthoma - Combined hyperlipidemia - Lecithin cholesterol acyltransferase deficiency - Tangier disease - Abetalipoproteinemia |
Fatty acid: Adrenoleukodystrophy - Acyl-coA dehydrogenase (Short-chain, Medium-chain, Long-chain 3-hydroxy, Very long-chain) - Carnitine (Primary, I, II)
|Mineral||Cu Wilson's disease/Menkes disease - Fe Haemochromatosis - Zn Acrodermatitis enteropathica - PO43− Hypophosphatemia/Hypophosphatasia - Mg2+ Hypermagnesemia/Hypomagnesemia - Ca2+ Hypercalcaemia/Hypocalcaemia/Disorders of calcium metabolism|
and acid-base balance
|Electrolyte disturbance - Na+ Hypernatremia/Hyponatremia - Acidosis (Metabolic, Respiratory, Lactic) - Alkalosis (Metabolic, Respiratory) - Mixed disorder of acid-base balance - H2O Dehydration/Hypervolemia - K+ Hypokalemia/Hyperkalemia - Cl− Hyperchloremia/Hypochloremia|
|Purine and pyrimidine||Hyperuricemia - Lesch-Nyhan syndrome - Xanthinuria|
|Porphyrin||Acute intermittent, Gunther's, Cutanea tarda, Erythropoietic, Hepatoerythropoietic, Hereditary copro-, Variegate|
|Bilirubin||Unconjugated (Lucey-Driscoll syndrome, Gilbert's syndrome, Crigler-Najjar syndrome) - Conjugated (Dubin-Johnson syndrome, Rotor syndrome)|
|Glycosaminoglycan||Mucopolysaccharidosis - 1:Hurler/Hunter - 3:Sanfilippo - 4:Morquio - 6:Maroteaux-Lamy - 7:Sly|
|Glycoprotein||Mucolipidosis - I-cell disease - Pseudo-Hurler polydystrophy - Aspartylglucosaminuria - Fucosidosis - Alpha-mannosidosis - Sialidosis|
|Other||Alpha 1-antitrypsin deficiency - Cystic fibrosis - Amyloidosis (Familial Mediterranean fever) - Acatalasia|