Intellectual Disability

This article provides an overview of intellectual disability, including the specific types, symptoms, causes, treatment options, and how to care for someone with an intellectual disability.

Key Takeaways:

• Intellectual disability is characterized by significant deficits in intellectual function and adaptive functioning. These make it hard to live independently, and may sometimes require full-time support, depending on the severity.

• The impairments are usually lifelong, but support and interventions can promote greater independence and improve quality of life.

• Treatment and support options include educational support, behavioral interventions, family education, and vocational training, among others.

Understanding Intellectual Disability

Intellectual disability (ID) is a neurodevelopmental disorder that appears during childhood. It is formally referred to as intellectual developmental disorder in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5).^[1]

Individuals with intellectual disability experience deficits in both intellectual functions, such as learning, reasoning, and abstract thinking, and adaptive functions, such as social skills, independent living activities, and the general ability to acquire and apply knowledge.^[1][2]

Symptoms can range from mild to severe, and thus, the level of assistance and care required depends on overall severity. Intellectual disability is generally a lifelong condition, although symptoms may vary in severity over time.^[1]

How Common is Intellectual Disability?

Intellectual disability affects approximately 1% to 3% of children worldwide, with around 85% of those cases classified as mild intellectual disability. Prevalences vary by region, with the condition affecting 1% to 1.5% of children in developing countries and up to 3% in more developed nations. Gender disparities have also been observed, with intellectual disability being approximately 1.5 times more common in males than females.^[1][2]

Types of Intellectual Disability

There are several specific types of intellectual disability, including:^[3]

• Down Syndrome

• Fragile X Syndrome

• Prader-Willi Syndrome

• Williams Syndrome

• Fetal Alcohol Spectrum Disorders

This is not an exhaustive list, but rather some of the most common types of ID.

Down Syndrome

Down syndrome is a chromosomal condition caused by an extra copy of chromosome 21. People with Down syndrome typically have a below-average IQ and may experience various developmental delays, such as with language, learning ability, and social and emotional skills.

Fragile X Syndrome

Fragile X syndrome is caused by a mutation in the FMR1 gene located on the X chromosome. Individuals with fragile X syndrome often experience several intellectual issues, including a low IQ, developmental delays, learning disabilities, and difficulty with language and math.

Individuals with this condition may also experience social and behavioral problems, such as social anxiety, impulsivity, and attention difficulties. Both males and females can have the disorder, but it is typically more severe in males.

Prader-Willi Syndrome

Prader-Willi syndrome is a genetic condition caused by genetic abnormalities on chromosome 15. It often results in a low IQ and cognitive impairments, such as speech/language deficits and poor short-term memory. Individuals with Prader-Willi syndrome may also exhibit behavioral problems such as tantrums and emotional regulation difficulties, along with delayed growth and development.

Williams Syndrome

Williams syndrome is a condition caused by the deletion of specific genes on chromosome 7. Individuals with Williams syndrome experience developmental delays and cognitive deficits, such as with learning, abstract thinking, and socializing.

Is Autism an Intellectual Disability?

Autism (or autism spectrum disorder) is characterized as a developmental disability, not an intellectual disability. While a significant percentage of individuals with ASD may also have a co-occurring intellectual disability, the two are distinct conditions. Not everyone with autism has intellectual impairment.

Symptoms

Symptoms of intellectual disability can generally be grouped into two categories: intelligence/intellectual-related symptoms and symptoms related to adaptive behaviors:^[1][2]

Intellectual Symptoms

• Lower intelligence than average (IQ below 70)

• Decreased reading speed

• Difficulty with reasoning and logic

• Trouble with critical thinking

• Difficulty solving problems

• Impaired working or short-term memory

• Difficulty with abstract thinking

Adaptive Behavior Symptoms

• Slower learning of self-care activities, such as bathing, dressing

• Delayed social development

• Little to no fear or apprehension of new people/strangers

• Difficulty carrying out chores or other daily tasks

• Difficulty understanding concepts, such as time management, managing money, etc.

• Trouble understanding social rules and boundaries

• Increased vulnerability to manipulation or exploitation

• Trouble understanding laws and rules

These symptoms vary from person to person depending on the overall severity of the condition. The DSM-5 categorizes intellectual disability into four severity levels: mild, moderate, severe, and profound.

Individuals with mild symptoms can often develop practical life skills and function well with minimal support. However, those with profound intellectual disability typically require close supervision and may be fully dependent on others for general functioning and daily living activities.^[1][2]

What Causes an Intellectual Disability?

Intellectual disability is often caused by genetic abnormalities, environmental factors, or both, although many specific causes are still unknown.

Examples of genetic causes of intellectual disability include:^[1][2]

• Down syndrome

• Fragile X syndrome

• Prader-Willi syndrome

• Williams syndrome

• Hunter Disease

• Hurler Disease

• Phenylketonuria

The most common genetic cause of ID is Down syndrome, affecting about 1 in 700 live births. The most common known inherited cause is Fragile X syndrome.^[4]

These genetic conditions involve abnormalities that cause defects in brain development or damage the brain and nervous system.

Environmental factors that may cause intellectual disability include:^[1][2]

• Alcohol exposure during pregnancy (fetal alcohol syndrome)

• Infections during fetal development (e.g., toxoplasmosis, rubella, HIV)

• Other fetal development disruptors (e.g., tobacco, various medications, radiation exposure)

• Premature birth

• Lack of oxygen (hypoxia) during birth

• Exposure to lead, mercury, and other heavy metals

• Infections in childhood, such as measles and meningitis

• Head trauma/injury

• Malnutrition

• Tumors or growths in the brain

Do All IDs Start from Birth?

Not all intellectual disabilities start from birth. While many cases of ID are caused by genetic or hereditary factors and thus begin in early development, some are acquired later, such as in cases of head trauma or childhood infection.

However, to meet the diagnostic criteria of an intellectual disability, the onset of deficits has to occur during the developmental period, specifically before the age of 22.

Conditions That Occur Alongside IDs

Many other mental disorders and health conditions commonly occur alongside IDs, with some disorders occurring 3 to 5 times more frequently in people with ID compared to the general population. Specific estimates have found that 30 to 42 percent of children with intellectual disability have a mental disorder, compared to just 6 to 7 percent of children without ID. Overall, at least 25 percent of all individuals with ID experience significant mental health challenges.^[4]

Examples of comorbid conditions are:^[1][2][4]

• Attention-deficit hyperactivity disorder (ADHD)

• Depressive and bipolar disorders

• Anxiety disorders

• ASD

• Communication disorders

• Impulse control disorders

• Movement disorders

• Major neurocognitive disorder

• Cerebral palsy

• Epilepsy

• Seizure disorders

Risks and Complications

Intellectual disability is associated with several risks and complications. For example, individuals with ID are 4 to 5 times more likely to develop mental health disorders or related comorbid conditions, which can significantly affect well-being, daily functioning, and overall life quality. Many individuals with ID also have poor self-esteem or a negative self-image, partly due to difficulties with social interactions and forming relationships.^[2][4]

Additionally, impairments in various adaptive functions may cause significant challenges with daily living, relationships, school, work, and family life. Individuals with ID may also be prone to self-injurious behaviors, aggression, or hyperactivity, which can increase the risk of harm and require close supervision.^[2]

Diagnosis

Diagnosing intellectual disability usually requires a multi-step process aimed at gaining a comprehensive understanding of the individual’s intellectual and adaptive functioning, including both strengths and weaknesses, while also evaluating for comorbid mental disorders and other conditions.

The first step of the diagnostic process involves a visit to a primary care physician. This includes a comprehensive medical history evaluation for the affected individual and, in pediatric cases, the mother. Additionally, your doctor will conduct a physical examination, which includes:

• Neurological testing

• Visual and hearing tests

• Motor function tests, such as for hypotonia and hyperreflexia

• Identification of physical characteristics often associated with various syndromes (e.g., Down syndrome, Fragile X syndrome, and Prader-Willi syndrome)

A psychiatrist or other qualified mental health professional may also assess for co-occurring mental disorders, although primary care doctors can sometimes provide initial screenings.

Following these initial assessments, standardized testing is conducted to evaluate intellectual ability and adaptive functioning. Results are compared against the criteria in theDSM-5, all three of which need to be met for a diagnosis:

• Deficits in intellectual function

• Deficits in adaptive function

• Onset of deficits during the developmental period

Intellectual ability is often measured through a standard IQ test, provided the individual is developmentally capable of completing them. Results on the IQ test are grouped into four levels of intellectual disability:^[2]

• Mild intellectual disability: IQ 50 to 70

• Moderate intellectual disability: IQ 35 to 50

• Severe intellectual disability: IQ 20 to 35

• Profound intellectual disability: IQ below 20

There are three specific measures of adaptive functioning:

• Conceptual

• Social

• Practical

These are assessed through standardized measures, such as:^[2][4]

• Adaptive Behavior Assessment System

• Vineland Adaptive Behavior Scales

These measures are usually supplemented with interviews of family members, teachers, and other relevant individuals.

Treatment and Management for Intellectual Disabilities

While ID cannot be cured, there are various treatment and support strategies that can improve daily functioning and quality of life, thus minimizing the condition’s negative impact for the individuals and those around them.

Detailed below are some of the most common and effective interventions for intellectual disability.^[1][2][4][5]

Educational Support

Special education enables individuals with ID to participate in school, while learning in an environment most appropriate for their abilities. Children with ID are often given a specialized education plan tailored to their unique needs, abilities, and goals. Through special education, individuals with ID also gain a variety of social, communication, behavioral, and general life skills.

Behavioral Interventions

A variety of behavioral interventions may be implemented to help promote positive behaviors and reduce negative or harmful behaviors. This typically involves cognitive and behavioral therapies that focus on positive reinforcement, avoiding triggers, redirecting undesirable behaviors, and promoting skill development, among other factors.

Vocational Training

Vocational training helps individuals with ID learn a variety of skills necessary to succeed in the workplace. This is done under the supervision of a multidisciplinary support team.

Family Education & Support

Family members of individuals with ID can also benefit from support services. These services help to:

• Educate family members on the nature of the disorder

• Guide families through placement decisions

• Make them aware of available resources and services

• Provide caregiver training

Government/Community Support

Local government agencies or support organizations can provide access to essential services, such as housing, food programs, and education and employment opportunities.

Medication

Medications are also frequently incorporated into the treatment plan to help manage comorbid mental disorders or other health conditions. Examples of common instances include:

• Selective-serotonin reuptake inhibitors (SSRIs) for anxiety and depressive disorders

• Antipsychotics for aggressive, disruptive, or self-injurious behaviors

• Various medications for ADHD (e.g. clonidine, methylphenidate)

Caring for Someone with an ID

Caring for someone with an ID can be emotionally challenging, stressful, and physically demanding. To support both the caregiver and the individual, consider the following strategies:

• Reach out for support, including caregiver training

• Stay in close contact with your doctor and all other professionals on the treatment team

• Detail any questions, comments, concerns, etc.

• Seek support from other family members and friends

• Partake in enjoyable activities with the individual

• Use clear and simple language

• Establish routines and schedules

• Focus on and encourage their strengths and abilities

• Use positive reinforcement and celebrate accomplishments, good behaviors, etc.

• Use visuals, gestures, and other aids