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 infantís 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