Intellectual Disability

Intellectual disability is a lifelong condition that affects how a person learns, thinks, and handles everyday tasks. While it presents unique challenges, most people with intellectual disability can live healthy, productive lives with the right support and services.

Table of contents

• What is Intellectual Disability?
• Signs and Symptoms
• What Causes Intellectual Disability?
• How Common is Intellectual Disability?
• How is Intellectual Disability Diagnosed?
• Treatment and Support
• Living with Intellectual Disability

What is Intellectual Disability?

Intellectual disability is a term used when a person has certain limitations in mental abilities and in skills needed for everyday life^[1]. These limitations cause a person to learn and develop more slowly or differently than others^[2]. The condition begins during childhood and continues throughout a person’s life^[1].

A common misunderstanding is that intellectual disability is just about intelligence as measured by an IQ test (a standardized test that measures mental abilities). However, an IQ test is only one piece of information. Some people have an average or above-average IQ but struggle with other abilities necessary for everyday life. Other people have lower-than-average IQs but also have strong enough skills and abilities that they don’t meet the criteria for intellectual disability, or they meet criteria for a milder form than an IQ test might suggest^[1].

The formal name for this condition in medical literature is “intellectual developmental disorder”^[1]. Although for many individuals the exact cause of their intellectual disability is unknown, many cases happen because of differences in brain development. Less commonly, they can develop because of brain damage from an illness, injury, or other events when a person is younger than 18 years old^[1].

Intellectual disability is characterized by significant limitations in both intellectual functioning and adaptive behavior (the collection of skills people learn to perform tasks in their everyday lives). The condition must originate before the age of 22^[5].

Signs and Symptoms

The symptoms of intellectual disability appear during childhood and involve difficulties in different skill areas, including academic skills, social skills, and practical everyday skills^[1].

Intelligence-related symptoms can include delayed or slowed learning of any kind, whether in school or from real-life experiences. A person may have slowed reading speed, difficulties with reasoning and logic, problems with judgment and critical thinking, and trouble using problem-solving and planning abilities. Distractibility and difficulty focusing are also common^[1].

Adaptive behavior limitations revolve around abilities and learned skills needed to live and support oneself independently. Children with intellectual disability may take longer to learn to speak, walk, and take care of personal needs such as dressing or eating^[4]. They may show slower learning of toilet training and self-care activities like bathing and dressing, and slower social development overall^[1].

Other signs include little or no fear of new people (lack of “stranger danger” behaviors), needing help from parents or other caregivers with basic daily activities past the expected age, difficulty learning how to do chores or other common tasks, and trouble understanding concepts like time management or money. A person may need help managing healthcare appointments or medications, have trouble understanding social boundaries, and experience difficulty with social interactions, including friendships and romantic relationships^[1].

Adaptive behaviors can be grouped into three types of skills. Conceptual skills include language and reading ability, and understanding concepts like money, time, and numbers. Social skills include interpersonal abilities, social responsibility, self-esteem, and the ability to follow rules and avoid being taken advantage of. Practical skills include activities of daily living such as personal care, job-related abilities, healthcare management, travel and transportation, maintaining schedules and routines, safety, and using money and the telephone^[5].

What Causes Intellectual Disability?

Doctors have found many causes of intellectual disability. The most common include genetic conditions, problems during pregnancy, problems at birth, and health problems during childhood^[4].

Genetic conditions can cause intellectual disability when abnormal genes are inherited from parents, when errors occur as genes combine, or for other genetic reasons. Examples of genetic conditions include Down syndrome, fragile X syndrome, and phenylketonuria (PKU)^[4].

Problems during pregnancy can result in intellectual disability when the baby does not develop properly inside the mother. There may be a problem with how the baby’s cells divide as it grows. A woman who drinks alcohol or gets an infection like rubella during pregnancy may also have a baby with an intellectual disability^[4].

Problems at birth can cause intellectual disability if a baby experiences difficulties during labor and delivery, such as not getting enough oxygen^[4].

Health problems during childhood can lead to intellectual disabilities. Diseases like whooping cough, measles, or meningitis can cause intellectual disabilities. They can also be caused by extreme malnutrition (not eating properly), not getting enough medical care, or being exposed to poisons like lead or mercury^[4].

It is important to understand that intellectual disability is not a disease. You cannot catch an intellectual disability from anyone. It is also not a type of mental illness, like depression^[4].

How Common is Intellectual Disability?

Intellectual disability is uncommon but widespread. Worldwide, it affects 1% to 3% of children. It is slightly more common in males than in females^[1].

According to various estimates, intellectual disability affects about 2% to 3% of the general population^[6]. It is estimated that seven to eight million people in the United States have an intellectual disability, which means that 1 in 10 families are affected^[4].

Most people with intellectual disability have a mild form of the condition. Seventy-five to ninety percent of affected people have mild intellectual disability, while about 6 per 1,000 individuals have severe intellectual disability^[6].

How is Intellectual Disability Diagnosed?

Intellectual disability is diagnosed based on three main criteria. First, there must be deficits in intellectual functioning such as reasoning, problem solving, planning, abstract thinking, judgment, academic learning, and learning from experience. These deficits must be confirmed by clinical evaluation and individualized standard IQ testing^[3].

Generally, an IQ test score of around 70 or as high as 75 indicates a significant limitation in intellectual functioning. IQ tests have a median of 100 and a standard deviation of 15, so a score of 70 or below represents two standard deviations below the population average^[5].

Second, there must be deficits in adaptive functioning that significantly hamper the person’s ability to meet developmental and sociocultural standards for independence and social responsibility^[3]. Standardized tests can determine limitations in adaptive behavior^[5].

Third, the onset of these deficits must occur during the developmental period, which is defined as before the age of 22^[3].

The diagnosis requires clinical evaluation and judgment as well as formal testing of cognitive and adaptive functions. Such formal testing is done by individually administered standardized tests^[12]. Only after a comprehensive evaluation can a clinician determine whether a person has intellectual disability^[5].

Additional factors must be taken into account when assessing intellectual disability, such as the community environment typical of the individual’s peers and culture. Professionals should also consider linguistic diversity and cultural differences in the way people communicate, move, and behave^[5].

Treatment and Support

There is no cure for intellectual disabilities. However, most children with an intellectual disability can learn to do many things. It just takes them more time and effort than other children^[4].

Treatments for children and adolescents with intellectual disabilities are based on an assessment of each individual’s social, educational, psychiatric, and environmental needs^[10].

Primary prevention focuses on eliminating or reducing the conditions that lead to the development of intellectual disability. Examples include screening babies for phenylketonuria (PKU) and administering a low-phenylalanine diet when PKU is present, which significantly reduces the emergence of intellectual disability. Education on the importance of abstaining from alcohol during pregnancy, optimal maternal and child healthcare, and family and genetic counseling for families with a history of intellectual disability are also important preventive measures^[10].

Secondary and tertiary prevention involves prompt attention to medical and psychiatric complications of intellectual disability, which can diminish their course and minimize the disability. Hereditary metabolic and endocrine disorders, such as PKU and hypothyroidism, can be treated effectively at an early stage by dietary control or hormone replacement therapy^[10].

Educational interventions for children with intellectual disabilities should include a comprehensive program that addresses academics and training in adaptive skills, social skills, and vocational skills. Particular attention should focus on communication and efforts to improve the child’s quality of life^[10].

Behavioral and cognitive-behavioral therapy has been used for many years to shape and enhance social behaviors and to control and minimize aggressive and destructive behaviors in individuals with intellectual disabilities. Positive reinforcement for desired behaviors and appropriate consequences for objectionable behaviors are helpful. Cognitive therapy, such as dispelling false beliefs and relaxation exercises, is also recommended for individuals who can follow instructions^[10].

Services should be provided within natural environments when possible, such as homes, child care, and educational, vocational, and community settings that include typical peers^[11]. A family-centered approach is well suited to individuals with intellectual disability because of the complexity of their health, educational, vocational, and community living challenges^[11].

Living with Intellectual Disability

Assessments must assume that limitations often coexist with strengths in a person, and that an individual’s level of life functioning will improve if appropriate, personalized supports are provided over a sustained period^[5].

A strengths-based perspective encourages practitioners to consider the potential and goals of an individual and their family. Challenges are acknowledged, yet strengths create a bridge to achieving valued life outcomes^[11].

Developing and maintaining functional communication to maximize self-sufficiency in individuals with intellectual disability is important to facilitate increased independence in the community. Every person has the right to participate fully in communication^[11].

With early recognition and appropriate support systems, most persons with intellectual disability can live healthy and productive lives^[12]. While most individuals have mild intellectual disability, those with severe intellectual disability may require life-long intensive supports^[12].

In addition to general medical care, persons with intellectual disability also need interventions in educational settings, provision of educational remediation and accommodations, and appropriate levels of community-based support^[12].

Community-based living provides more opportunity for communicating with a variety of individuals, improving quality of life, and offering new learning opportunities. Educational and community programs, including postsecondary programs, employment opportunities, and more independent living options for persons with intellectual disability are now the norm^[11].

A future plan is a guide for people with intellectual disabilities to lead a good life as independently as possible. It can also help people with intellectual disability reach their goals and dreams. A future plan is important for all families, especially when a parent or caregiver is no longer able to support a person with intellectual disability^[21].