Mental retardation - Overview
Intellectual and developmental disability
Definition of Mental retardation:
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.
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)
- Chromosomal abnormalities
- Chromosome deletions (such as 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 (such as fragile X syndrome, Angelman syndrome, Prader-Willi syndrome)
- Errors of chromosome numbers (such as Down syndrome)
- Genetic abnormalities and inherited metabolic disorders
- Congenital hypothyroid
- Hypoglycemia (poorly regulated diabetes)
- Reye syndrome
- Hyperbilirubinemia (very high bilirubin levels in babies)
- Trauma (before and after birth)
- Intracranial hemorrhage before or after birth
- Lack of oxygen to the brain before, during, or after birth
- Severe head injury
- Unexplained (this largest category is for unexplained occurrences of mental retardation)
- Reviewed last on: 5/1/2011
- 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.
Shapiro BK, Batshaw ML. Mental retardation (intellectual disability). In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 38.
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