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.
Intellectual disability affects about 1% to 3% of the population. There are many causes of intellectual disability, but doctors find a specific reason in only 25% of cases.
Risk factors are related to the causes. Causes of intellectual disability can include:
Infections (present at birth or occurring after birth)
Chromosomal abnormalities (such as Down syndrome)
Metabolic (such as hyperbilirubinemia, 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 (this largest category is for unexplained occurrences of intellectual disability)
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
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. Persons with intellectual disability are often helped with behavioral counseling.
Discuss your child’s treatment and support options with your health care provider or social worker so that you can help your child reach his or her full potential.
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
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
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.
Shapiro BK, Batshaw ML. Intellectual disability. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 33.
Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.