Mental retardation
Key points
- Mental retardation is described as below-average general intellectual function with associated deficits in adaptive behavior that occurs before age 18.
- Causes of mental retardation are numerous, but a specific reason for mental retardation is determined in only 25% of the cases.
- Note: Deviations in normal adaptive behaviors depend on the severity of the condition.
- The primary goal of treatment is to develop the person's potential to the fullest.
Definition
Mental retardation is described as below-average general intellectual function with associated deficits in adaptive behavior that occurs before age 18.
Causes, incidence, and risk factors
Causes of mental retardation are numerous, but a specific reason for mental retardation is determined in only 25% of the cases.
Failure to adapt normally and grow intellectually may become apparent early in life or, in the case of mild retardation, not become recognizable until school age or later. An assessment of age-appropriate adaptive behaviors can be made by the use of developmental screening tests. The failure to achieve developmental milestones is suggestive of mental retardation.
A family may suspect mental retardation if motor skills, language skills, and self-help skills do not seem to be developing in a child or are developing at a far slower rate than the child's peers.
The degree of impairment from mental retardation has a wide range from profoundly impaired to mild or borderline retardation. Less emphasis is now placed on degree of retardation and more on the amount of intervention and care required for daily life.
Risk factors are related to the causes. Mental retardation affects about 1 to 3% of the population.
Causes of mental retardation can be roughly broken down into several categories:
- unexplained (This category is the largest and a catchall for undiagnosed incidences of mental retardation.)
- trauma (prenatal and postnatal)
o intracranial hemorrhage before or after birth (for example, periventricular hemorrhage)
o lack of oxygen to the brain before, during, or after birth
o severe Head injury - infectious (congenital and postnatal)
o congenital rubella
o Meningitis
o congenital CMV
o encephalitis
o Congenital toxoplasmosis
o listeriosis
o HIV infection - chromosomal abnormalities
o errors of chromosome numbers (Down's syndrome)
o defects in the chromosome or chromosomal inheritance (fragile X syndrome, Angelman syndrome, Prader-Willi syndrome)o chromosomal translocations (a gene is located in an unusual spot on a chromosome, or location on a different chromosome than usual) and deletions (cri du chat syndrome)
Written and revised by
Gerald Hurowitz, M.D.
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