Definition

Intellectual disability is a condition diagnosed before age 18 that includes below-average intellectual function and a lack of skills necessary for daily living.

In the past, the term mental retardation was used to describe this condition. This term is no longer used.

Alternative Names

Intellectual developmental disorder; Mental retardation

Causes

Intellectual disability affects about 1% of the population. There are many causes of intellectual disability.

Risk factors are specific to the cause of intellectual disability. Causes of intellectual disability can include:

• Infections (present at birth or occurring after birth)
• Chromosomal abnormalities (such as Down syndrome)
• Environmental (such as lead)
• Metabolic (such as hyperbilirubinemia, or very high bilirubin levels in babies)
• Nutritional (such as malnutrition)
• Toxic (intrauterine exposure to alcohol, cocaine, amphetamines, and other drugs)
• Trauma (before and after birth)
• Unexplained (health care providers do not know the reason for the person's intellectual disability)

Symptoms

As a family, you may suspect your child has an intellectual disability when your child has any of the following:

• Lack of or slow development of motor skills, language skills, and self-help skills, especially when compared to peers
• Failure to grow intellectually or continued infant-like behavior
• Lack of curiosity
• Problems keeping up in school
• Failure to adapt (adjust to new situations)
• Difficulty understanding and following social rules

Signs of intellectual disability can range from mild to severe.

Exams and Tests

Developmental tests are often used to assess the child:

• 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 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 physical and mental health problems. People with intellectual disability are often helped with behavioral counseling.

Discuss your child's treatment and support options with your provider or social worker so that you can help your child reach their full potential.

Support Groups

More information and support for people with intellectual disability and their families can be found at:

• American Association on Intellectual and Developmental Disabilities - www.aaidd.org/
• The Arc - thearc.org/
• National Association for Down Syndrome - www.nads.org/

Outlook (Prognosis)

Outcome depends on:

• Severity and cause of the intellectual disability
• Other conditions
• Treatment and therapies

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

When to Contact a Medical Professional

Contact your 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. Genetic counseling and screening during pregnancy can help parents understand risks and make plans and decisions.

Social. Nutrition programs can reduce disability associated with malnutrition. Early intervention in situations involving abuse and poverty will also help.

Toxic. Preventing exposure to lead, mercury, and other toxins reduces the risk of disability. Teaching women about the risks of alcohol and drugs during pregnancy can also help reduce risk.

Infectious diseases. Certain infections can lead to intellectual disability. Preventing these diseases reduces the risk. For example, rubella syndrome can be prevented through vaccination. Avoiding exposure to cat feces that can cause toxoplasmosis during pregnancy helps reduce disability from this infection.

References

American Psychiatric Association website. Intellectual disability. www.psychiatry.org/patients-families/intellectual-disability/what-is-intellectual-disability. Updated August 2021. Accessed May 23, 2023.

Shapiro BK, O'Neill ME. Developmental delay and intellectual disability. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 21st ed. Philadelphia, PA: Elsevier; 2020:chap 53.