Mental retardation

Mental retardation (also called mental handicap and, as defined by the UK Mental Health Act (1983), mental impairment and severe mental impairment) is a term for a pattern of persistently slow learning of basic motor and language skills ("milestones") during childhood, and a significantly below-normal global intellectual capacity as an adult. One common criterion for diagnosis of what used to be called mental retardation is a tested intelligence quotient (IQ) below 70.

Causes

Doctors have found many causes. The most common are:

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• Genetic conditions. Sometimes disability is caused by abnormal genes inherited from parents, errors when genes combine, or other reasons. Examples of genetic conditions include Down syndrome, Fragile X syndrome, and phenylketonuria (PKU).
• Problems during pregnancy. Mental disability can result when the baby does not develop inside the mother properly. For example, there may be a problem with the way the baby's cells divide as it grows. A woman who drinks alcohol (see fetal alcohol syndrome) or gets an infection like rubella during pregnancy may also have a baby with mental disability.
• Problems at birth. If a baby has problems during labor and birth, such as not getting enough oxygen, he or she may have developmental disability.
• Health problems. Diseases like whooping cough, the measles, or meningitis can cause mental disability. It can also be caused by extreme malnutrition, not getting enough medical care, or by being exposed to poisons like lead or mercury.
• Iodine deficiency is the leading, preventable cause of mental disability in areas of the developing world where iodine deficiency is endemic.