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Disorders of Metabolism in Childhood

Description

Metabolism refers to how the body processes substances needed to carry out its functions. Most metabolic diseases are caused by single defects in particular biochemical pathways, defects that are most often due to the deficient activity of individual enzymes (which are needed to stimulate a metabolic process) on a substrate (starting material). Genetic abnormalities are often at the root of this deficient activity.
Metabolic disorders in childhood are usually carbohydrate metabolism disorders or pyruvate metabolism disorders .

Substrate  +   Enzyme   =   Product

The potential consequences of mutant enzymes on cellular or organ function are varied and may include:

  1. The product of the affected metabolic pathway may have a key role that is not fulfilled.
  2. A metabolic pathway that is repressed by normal levels of the product may proceed, with toxic consequences, when that product is at low levels.
  3. Excess substrate from the affected reaction may be toxic.
  4. The excess substrate may become involved in and move rapidly through an alternate metabolic pathway, and the product of this pathway may be toxic.

About 170 errors of metabolism can be traced to mutations in the genetic code, and the consequences range from trivial to lethal.

Diagnosis and Treatment

If an inborn error of metabolism (inherited) is suspected, diagnosis can be at several different levels:

  • A thorough family history in order to analyse the pattern of inheritance.
  • Blood or urine tests to determine whether the substrate and the product of the suspect biochemical reaction are at normal levels.
  • The activity of the suspect enzyme may be measured in red or white blood cells, in tissue samples, or in skin cells grown in test tube cultures.
  • The number of enzyme molecules may be measured in blood or tissue samples.
  • The DNA molecule that codes for the suspected abnormal enzyme may be isolated from blood cells, and its nucleotide base sequence determined and identified as mutant.
  • Testing also may be applied to parents, siblings, or offspring of the affected person.

The diagnosis of a treatable condition may be made through screening at birth. A severe metabolic disorder may be diagnosed in the foetus by using samples from the amniotic fluid surrounding the embryo. The information is then available for counselling or sometimes for initiating treatment before birth.
A variety of treatments are available for metabolic disorders. These include:

  • Provision of the product of the reaction, if deficient.
  • If the high level of substrate is toxic, diet restrictions may help reduce levels by activating its removal from the body, or by preventing its synthesis at an earlier step.
  • Enzyme activity may be increased by administering a 'cofactor' or certain drugs.
  • The enzyme deficiency may be replaced with normal enzyme, although this approach has been successful only rarely.

The information in this page is presented in summarised form and has been taken from the following source(s):
1. The Encycloædia Britannica© Online: http://www.britannica.com/


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  http://www.hon.ch/Dossier/MotherChild/child_metabolism/child_metabolism.html Last modified: Jun 25 2002