Intellectual Disability

What is Intellectual Disability?

Intellectual disability¹ involves problems with general mental abilities that affect functioning in two areas:

• intellectual functioning (such as learning, problem solving, judgement)
• adaptive functioning (activities of daily life such as communication and independent living)

Intellectual disability affects about one percent of the population, and of those about 85 percent have mild intellectual disability. Males are more likely than females to be diagnosed with intellectual disability.

• Diagnosis

  Diagnosing Intellectual Disability

  Intellectual disability is identified by problems in both intellectual and adaptive functioning.

  Intellectual functioning is assessed with an exam by a doctor and through standardized testing. While a specific full-scale IQ test score is no longer required for diagnosis, standardized testing is used as part of diagnosing the condition. A full scale IQ score of around 70 to 75 indicates a significant limitation in intellectual functioning.² However, the IQ score must be interpreted in the context of the person’s difficulties in general mental abilities. Moreover, scores on subtests can vary considerably so that the full scale IQ score may not accurately reflect overall intellectual functioning.

  Three areas of adaptive functioning are considered:

  1. Conceptual – language, reading, writing, math, reasoning, knowledge, memory
  2. Social – empathy, social judgment, communication skills, the ability follow rules and the ability to make and keep friendships
  3. Practical – independence in areas such as personal care, job responsibilities, managing money, recreation and organizing school and work tasks

  Adaptive functioning is assessed through standardized measures with the individual and interviews with others, such as family members, teachers and caregivers.

  Intellectual disability is identified as mild (most people with intellectual disability are in this category), moderate or severe. The symptoms of intellectual disability begin during childhood or adolescence. Delays in language or motor skills may be seen by age two. However, mild levels of intellectual disability may not be identified until school age when a child may have difficulty with academics.

• Causes

  Causes

  There are many different causes of intellectual disability. It can be associated with a genetic syndrome, such as Down syndrome and Fragile X syndrome. It may develop following an illness such as meningitis, whooping cough or measles; may result from head trauma during childhood; or may result from exposure to toxins such as lead or mercury. Other factors that may contribute to intellectual disability include brain malformation, maternal disease and environmental influences (alcohol, drugs or other toxins). A variety of labor- and delivery-related events, infection during pregnancy and problems at birth, such as not getting enough oxygen, can also contribute.

• Treatment

  Treatment

  Intellectual disability is a life-long condition. However, early and ongoing intervention may improve functioning and enable the person to thrive throughout their lifetime. It may also be influenced by underlying medical or genetic conditions and co-occurring conditions.

  Once a diagnosis is made, help for individuals with intellectual disability is focused on looking at the individual’s strengths and needs, and the supports he or she needs to function at home, in school/work and in the community.

  Services for people with intellectual disabilities and their families provide support to allow full inclusion in the community. Many different types of supports and services can help, such as:

  • Early intervention (infants and toddlers)
  • Special education
  • Family support (for example, respite care)
  • Transition services
  • Vocational programs
  • Day programs
  • Housing options
  • Case management

  Under federal law (Individuals with Disabilities Education Act, IDEA, 1990), early intervention services work to identify and help infants and toddlers with disabilities. Federal law also requires that special education and related services are available free to every eligible child with a disability, including intellectual disability.

  In addition, supports can come from family, friends, co-workers, community members or from a service system. Job coaching is one example of a support that can be provided by a service system. With proper support, people with intellectual disabilities are capable of successful, productive roles in society.

  A diagnosis often determines eligibility for services and protection of rights, such as special education services and home and community services. The American Association of Intellectual and Developmental Disabilities (AAIDD) stresses that the main reason for evaluating individuals with intellectual disabilities is to be able to identify and put in place the supports and services that will help them thrive in the community throughout their lives.

Related and co-occurring conditions

Some mental health, neurodevelopmental, medical and physical conditions frequently co-occur in individuals with intellectual disability, including cerebral palsy, epilepsy, ADHD, autism spectrum disorder and depression and anxiety disorders. Identifying and diagnosing co-occurring conditions can be challenging, for example recognizing depression in an individual with limited verbal ability. However, accurate diagnosis and treatment are important for a healthy and fulfilling life for any individual.

• Attention-deficit/hyperactivity disorder
• Autism spectrum disorder
• Social communication disorder
• Specific learning disorder

Tips for parents

• Learn about your child’s disability
• Connect with other parents of children with disabilities
• Be patient; learning may come slower for your child
• Encourage independence and responsibility
• Look for opportunities in your community for social, recreational and sports activities (such as Best Buddies or Special Olympics)

References and Resources

Physician Review By:

Ranna Parekh, M.D., M.P.H.,
July 2017