Intellectual disability 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 disability affects about 1 - 3% of the population. There are many causes of intellectual disability, but doctors find a specific reason in only 25% of cases.
A family may suspect intellectual disabilityif 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 intellectual disability, these failures may not become recognizable until school age or later.
The degree of impairment from intellectual disability varies widely, from profoundly impaired to mild or borderline disability. Less emphasis is now placed on the degree of disability and more on the amount of intervention and care needed for daily life.
Risk factors are related to the causes. Causes of intellectual disability 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 intellectual disability)
- Continued infant-like behavior
- Decreased learning ability
- Failure to meet the markers of intellectual development
- Inability to meet educational demands at school
- Lack of curiosity
Note: Changes to normal behaviors depend on the severity of the condition. Mild disability may be associated with a lack of curiosity and quiet behavior. Severe intellectual disability is associated with infant-like behavior throughout life.
Exams and Tests
An assessment of age-appropriate adaptive behaviors can be made using developmental screening tests. The failure to achieve developmental milestones suggests intellectual disability.
The following may be signs of intellectual disability:
- 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
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 intellectual disability.
The outcome depends on:
- Other conditions
- Personal motivation
Many people lead productive lives and function on their own; others need a structured environment to be most successful.
Complications vary. They may include:
- Inability to care for self
- Inability to interact with others appropriately
- Social isolation
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: Prenatal screening for genetic defects and genetic counseling for families at risk for known inherited disorders can decrease the risk of inherited intellectual disability.
Social: Government nutrition programs are available to poor children in the first and most critical years of life. These programs can reduce disability associated with malnutrition. Early intervention in situations involving abuse and poverty will also help.
Toxic: Environmental programs to reduce exposure to lead, mercury, and other toxins will reduce toxin-associated disability. 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 disability.
Infectious: The prevention of congenital rubella syndrome is probably one of the best examples of a successful program to prevent one form of intellectual disability. Constant vigilance, such as limiting exposure to cat litter that can cause toxoplasmosis during pregnancy, helps reduce disability that results 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: Saunders Elsevier; 2011:chap 33.
A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team. Previously reviewed by Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine (5/1/2011).
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