Health Encyclopedia

Mental retardation

Definition

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.

An assessment of age-appropriate adaptive behaviors can be made using developmental screening tests. The failure to achieve developmental milestones suggests mental retardation.

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 (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)
Environmental
- 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
Metabolic
- Congenital hypothyroid
- Hypoglycemia (poorly regulated diabetes mellitus)
- Reye syndrome
- Hyperbilirubinemia (very high bilirubin levels in babies)
Nutritional
- Malnutrition
Toxic
- Intrauterine exposure 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
- Severe head injury
Unexplained (this largest category is for unexplained occurrences of mental retardation)

Symptoms

Continued infantile behavior
Decreased learning ability
Failure to meet intellectual developmental markers
Inability to meet educational demands at school
Lack of curiosity

Note: Changes to normal behaviors depend on the severity of the condition. Mild retardation may be associated with a lack of curiosity and quiet behavior. Severe mental retardation is associated with infantile behavior throughout life.

Signs and tests

Abnormal Denver developmental screening test
Adaptive behavior score below average
Development way below that of peers
Intelligence quotient (IQ) score below 70 on a standardized IQ test

Treatment

The primary goal of treatment is to develop the person's potential to the fullest. Special education and training may begin as early as infancy. This includes social skills to help the person function as normally as possible.

It is important for a specialist to evaluate the person for other affective disorders and treat those disorders. Behavioral approaches are important for people with mental retardation.

Expectations (prognosis)

The outcome depends on:

Opportunities
Other conditions
Personal motivation
Treatment

Many people lead productive lives and function on their own; others need a structured environment to be most successful.

Complications

Complications vary. They may include:

Inability to care for self
Inability to interact with others appropriately
Social isolation

Calling your health care provider

Call your health care provider if:

You have any concerns about your child's development
You notice that your child's motor or language skills are not developing normally
Your child has other disorders that need treatment

Prevention

Genetic: Prenatal screening for genetic defects and genetic counseling for families at risk for known heritable disorders can decrease the incidence of genetically caused mental retardation.

Social: Government programs to ensure adequate nutrition are available to the underprivileged in the first and most critical years of life. These programs can reduce retardation associated with malnutrition. Early intervention in situations involving abuse and deprivation will also help.

Toxic: Environmental programs to reduce exposure to lead, mercury, and other toxins will reduce toxin-associated retardation. However, the benefits may take years to become apparent. Increased public awareness of the risks of alcohol and drugs during pregnancy can help reduce the incidence of retardation.

Infectious: The prevention of congenital rubella syndrome is probably one of the best examples of a successful program to prevent one form of mental retardation. Constant vigilance, such as limiting exposure to cat litter that can cause toxoplasmosis during pregnancy, helps reduce retardation that results from this infection.

Review Date:11/12/2007
Reviewed By:Rachel A. Lewis, M.D., F.A.A.P., Columbia University Pediatric Faculty Practice, New York, NY. Review provided by VeriMed Healthcare Network.

ADAM Quality A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org). URAC's accreditation program is the first of its kind, requiring compliance with 53 standards of quality and accountability, verified by independent audit. A.D.A.M. is among the first to achieve this important distinction for online health information and services. Learn more about A.D.A.M.'s editorial process. A.D.A.M. is also a founding member of Hi-Ethics (www.hiethics.com) and subscribes to the principles of the Health on the Net Foundation (www.hon.ch).

The Agency for Health Care Administration (Agency) and this website do not claim the information on, or referred to by, this site is error free. This site may include links to websites of other government agencies or private groups. Our Agency and this website do not control such sites and are not responsible for their content. Reference to or links to any other group, product, service, or information does not mean our Agency or this website approves of that group, product, service, or information.

Additionally, while health information provided through this website may be a valuable resource for the public, it is not designed to offer medical advice. Talk with your doctor about medical care questions you may have.