What Causes Mental Retardation
Mental retardation can be caused by any condition which impairs development of the brain
before birth, during birth or in the childhood years. Several hundred causes have been
discovered, but in about one-third of the people affected, the cause remains unknown. The
three major known causes of mental retardation are Down syndrome, fetal alcohol syndrome
and fragile X.
The causes can be categorized as follows:
· Genetic conditions - These result from abnormality of genes inherited 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. Inborn errors of metabolism which
may produce mental retardation, such as PKU (phenylketonuria), fall in this category.
Chromosomal abnormalities have likewise been related to some forms of mental retardation,
such as Down syndrome and fragile X syndrome.
· Problems during pregnancy - Use of alcohol or drugs by the pregnant mother can cause
mental retardation. Malnutrition, rubella, glanular disorders and diabetes,
cytomegalovirus, and many other illneses of the mother during pregnancy may result in a
child being born with mental retardation. Physical malformations of the brain and HIV
infection originating in prenatal life may also result in mental retardation.
· Problems at birth - Although any birth condition of unusual stress may injure the
infants brain, prematurity and low birth weight predict serious problems more often
than any other conditions.
· Problems after birth - Childhood diseases such as whooping cough, chicken pox, measles,
and Hib disease which may lead to meningitis and encephalitis can damage the brain, as can
accidents such as a blow to the head or near drowning. Substances such as lead and mercury
can cause irreparable damage to the brain and nervous system.
· Poverty and cultural deprivation - Children in poor families may become mentally
retarded because of malnutrition, disease-producing conditions, inadequate medical care
and environmental health hazards. Also, children in disadvantaged areas may be deprived of
many common cultural and day- to-day experiences provided to other youngsters. Research
suggests that such under-stimulation can result in irreversible damage and can serve as a
cause of mental retardation.
Back to Issue - January 1997
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