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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):
- 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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