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Causes of Mental Retardation
Mental retardation can be caused by any condition which impairs the development of the brain before birth, during
birth or in the childhood years. While several hundred causes of mental retardation have been discovered, for at
least one-third of the individuals affected the cause remains unknown.
There are various causes of mental retardation, most commonly:
- Genetic conditions: Sometimes mental retardation can be caused by genetic problems such as a change in a gene
(mutation) or disruption of gene(s) because of a deletion, addition or rearrangement of the genetic material.
Genetic problems include both those that run in families and those that have appeared for the first time in the
individual who is affected. Examples of genetic conditions include Fragile X syndrome, Down syndrome, and
phenylketonuria (PKU).
- Problems during pregnancy: Mental retardation may result from problems with the baby’s development during
pregnancy. For instance, use of alcohol or drugs by the pregnant mother can cause mental retardation. Also, severe
malnutrition, infections or exposure to toxins during pregnancy can affect the baby’s brain development.
- Problems at birth: Problems during labor and birth, such as lack of oxygen to the brain, can cause mental
retardation.
- Problems during childhood: Mental retardation can also be caused by childhood diseases, severe head injury, or
exposure to toxins or poisons.
Many of the genetic causes of mental retardation remain unknown. One of the primary goals of our laboratory is to
find genes that cause mental retardation. We have identified one gene so far, PAK3, which causes non-syndromic
(without other medical concerns) X-linked mental retardation (Allen et al, Nat Genet 20: 25-30, 2000).
Our hope is that understanding more about genes that cause mental retardation may lead to improved diagnosis and
management.
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