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II. WHAT CAUSES MENTAL RETARDATION/DEVELOPMENTAL DISABILITIES?
Causes related to mental retardation are categorized as follows (S. Miller, Personal communication, May 2001):
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Genetic conditions - abnormality of genes passed on from parents, errors when genes combine, or from other disorders of the genes caused during pregnancy by infections, overexposure to x-rays and other factors cause mental retardation. Over 500 genetic diseases are associated with mental retardation, including:
- PKU (phenylketonuria): a single gene disorder also referred to as an inborn error of metabolism due to a defective enzyme.
- Down syndrome: a chromosomal disorder caused by too many or too few chromosomes, or by a change in structure of a chromosome.
- Fragile X syndrome: a single gene disorder located on the X chromosome that is the leading inherited cause of mental retardation.
Other factors that may cause or increase the possibility of mental retardation include:
- Substance abuse or usage - use of alcohol, tobacco, or other drugs during pregnancy.
- Sexually transmitted diseases - pregnant women who are infected with syphilis, HIV, or other diseases may pass them on to their child leading to future neurological damage.
- Birth conditions - any birth condition resulting in unusual stress that injures the infant's brain, prematurity, and low birth weight.
- Early childhood diseases - whooping cough, chicken pox, measles, and Hib disease (which can lead to meningitis and encephalitis).
- Trauma - accidents such as a blow to the head, child abuse, or near drowning.
- Environmental - certain environmental contaminants, and illnesses of the mother during pregnancy, such as toxoplasmosis, cytomegalovirus, rubella, lead or, mercury exposure, and other environmental toxins.
- Conditions often associated with poverty - malnutrition, disease-producing conditions, inadequate medical care, and under-stimulation.
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