Mental retardation is a condition diagnosed before age 18 that includes below-average general intellectual function, and a lack of the skills necessary for daily living.
Intellectual and developmental disability
Causes, incidence, and risk factors
Mental retardation affects about 1 - 3% of the population. There are many causes of mental retardation, but doctors find a specific reason in only 25% of cases.
A family may suspect mental retardation if the child's motor skills, language skills, and self-help skills do not seem to be developing, or are developing at a far slower rate than the child's peers. Failure to adapt (adjust to new situations) normally and grow intellectually may become apparent early in a child's life. In the case of mild retardation, these failures may not become recognizable until school age or later.
The degree of impairment from mental retardation varies widely, from profoundly impaired to mild or borderline retardation. Less emphasis is now placed on the degree of retardation and more on the amount of intervention and care needed for daily life.
Risk factors are related to the causes. Causes of mental retardation can be roughly broken down into several categories:
- Infections (present at birth or occurring after birth)
Congenital CMV Congenital rubella Congenital toxoplasmosis Encephalitis HIV infection Listeriosis Meningitis
- Chromosomal abnormalities
- Chromosome deletions (
cri du chat syndrome)
- Chromosomal translocations (a gene is located in an unusual spot on a chromosome, or located on a different chromosome than usual)
- Defects in the chromosome or chromosomal inheritance (for example,
fragile X syndrome, Angelman syndrome, Prader-Willi syndrome)
- Errors of chromosome numbers (such as Down syndrome)
- Chromosome deletions (
- Deprivation syndrome
- Genetic abnormalities and inherited metabolic disorders
Adrenoleukodystrophy Galactosemia Hunter syndrome Hurler syndrome
- Lesch-Nyhan syndrome
Phenylketonuria Rett syndrome Sanfilippo syndrome Tay-Sachs disease Tuberous sclerosis
- Congenital hypothyroid
- Hypoglycemia (poorly regulated diabetes)
- Hyperbilirubinemia (very high
bilirubinlevels in babies)
Intrauterineexposure to alcohol, cocaine, amphetamines, and other drugs Lead poisoning Methylmercury poisoning
- Trauma (before and after birth)
- Intracranial hemorrhage before or after birth
- Lack of oxygen to the brain before, during, or after birth
- Unexplained (this largest category is for unexplained occurrences of mental retardation)
Review Date: 11/02/2009
Reviewed By: Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.