Metabolism, inborn errors of

Inherited defects of body chemistry. Inborn errors of metabolism are caused by single gene defects, which lead to abnormal functioning of an enzyme. Some of these gene defects are harmless, but others are severe enough to result in death or physical or mental handicap. Examples include Tay–Sachs disease, phenylketonuria, Hurler’s syndrome, and Lesch–Nyhan syndrome. Collectively, inborn errors of metabolism affect around 1 child in 5,000. Symptoms are usually present at or soon after birth. They may include unexplained illness or failure to thrive, developmental delay, floppiness, persistent vomiting, or seizures. Routine tests are performed on newborn babies for some genetic disorders, such as phenylketonuria. Treatment is not needed for some inborn errors of metabolism. For others, avoidance of a specific environmental factor may be sufficient. In some cases, the missing enzyme or the protein that it produces can be manufactured using genetic engineering techniques, or a vitamin supplement can help compensate for the defective enzyme. If the enzyme is made in blood cells, a bone marrow transplant may provide a cure. People with a child or a close relative who is affected may benefit from genetic counselling before planning a pregnancy.