Inborn error of metabolism

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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.

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 work that prefigured the "one gene-one enzyme" hypothesis, based on 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.

Incidence

In a study in British Columbia, the overall incidence of the inborn errors of metabolism were estimated to be 70 per 100,000 live births or 1 in 1,400 births,[1] overall representing more than approximately 15% of single gene disorders in the population.[1]

Type of inborn error Incidence
Disease involving amino acids (e.g. PKU), organic acids,
primary lactic acidosis, galactosemia, or a urea cycle disease
24 per 100 000 births[1] 1 in 4,200[1]
Lysosomal storage disease 8 per 100 000 births[1] 1 in 12,500[1]
Peroxisomal disorder ~3 to 4 per 100 000 of births[1] ~1 in 30,000[1]
Respiratory chain-based mitochondrial disease ~3 per 100 000 births[1] 1 in 33,000[1]
Glycogen storage disease 2.3 per 100 000 births[1] 1 in 43,000[1]

Signs and symptoms

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: many manifestations may develop

Diagnosis

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. There is a revolutionary GC/MS based technology with an integrated analytics system, which has now made it possible to test a newborn for over 100 genetic metabolic disorders.

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):

Treatment

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 past twenty years, enzyme replacement, gene therapy, and organ transplantation have become available and beneficial for many previously untreatable disorders. Some of the more common or promising therapies are listed:

  • Dietary restriction
  • Dietary supplementation or replacement
  • Vitamins
  • Intermediary metabolites, compounds, or drugs that facilitate or retard specific metabolic pathways
  • Dialysis
  • Enzyme replacement E.g. Acid-alpha glucosidase for Pompe disease
  • Gene therapy
  • Bone marrow or organ transplantation
  • Treatment of symptoms and complications
  • Prenatal diagnosis and avoidance of pregnancy or abortion of an affected fetus

References

  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11

External links

The National Institutes of Health offers theoffice of rare diseases, home reference, medlineplus andhealth information. The National Human Genome Research Institute hosts an information center, a section forpatients and the public and additionaleducational resources. Support groups can be found atNORD, Genetic Alliance and Orphanet. The genetic education center at the KUMC has many more useful links.

Template:Medical conditions Template:Carbohydrate metabolic pathology Template:Amino acid metabolic pathology Template:Fatty-acid metabolism disorders Template:Lipid metabolism disorders Template:Heme metabolism disorders Template:Inborn errors of purine-pyrimidine metabolism Template:Other metabolic pathology Template:Defects of steroid metabolism Template:Metabolic disorders of vitamins, coenzymes, and cofactors

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