Intellectual Disabilities – DSM-5 Definition

 

According to the DSM-5 (Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition), Intellectual Disability (also called Intellectual Developmental Disorder) is a neurodevelopmental disorder that begins before the age of 18.
It is characterized by significant limitations in:

1. Intellectual functioning – such as reasoning, problem-solving, planning, abstract thinking, academic learning, and judgment.

2. Adaptive functioning – how well a person meets community standards of personal independence and social responsibility, in three domains:

   • Conceptual (language, reading, writing, math, memory, reasoning)

   • Social (empathy, social judgment, friendships, communication)

   • Practical (personal care, money management, organizing tasks, work skills)

These difficulties affect everyday life and are not due to temporary problems such as lack of education or cultural differences.

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Levels of Severity

DSM-5 recognizes four levels, based on adaptive functioning (not IQ alone):

1. Mild

2. Moderate

3. Severe

4. Profound

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Possible Causes

Intellectual disabilities can result from many factors, including:

• Genetic conditions (e.g., Down syndrome, Fragile X syndrome, Williams syndrome, Prader–Willi syndrome, Apert syndrome, phenylketonuria/PKU)

• Prenatal factors (alcohol/drug exposure, malnutrition, infections such as rubella)

• Perinatal factors (birth complications, oxygen deprivation)

• Postnatal factors (head injury, brain infections, neglect)

• Metabolic disorders

• Sometimes, the cause is unknown.

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Common Examples of Intellectual Disabilities

• Fragile X Syndrome

• Down Syndrome

• Prader–Willi Syndrome

• Williams Syndrome

• Phenylketonuria (PKU)

• Apert Syndrome

• Brain injury or trauma (if it occurs before adulthood)

• Cerebral Palsy (when accompanied by intellectual impairment)

• Epilepsy (in some cases)

Note: Autism Spectrum Disorder (ASD) is not automatically an intellectual disability, but it can occur alongside ID.

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Signs and Symptoms

• Delayed milestones (sitting, crawling, walking, talking)

• Speech that may be difficult to understand at first

• Learning difficulties (reading, writing, mathematics)

• Trouble with problem-solving and abstract thinking

• Difficulty understanding social rules and norms

• Short-term memory challenges

• Needing support for daily living skills (personal care, money management, organizing, work)

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Related/Co-Occurring Conditions

• Autism Spectrum Disorder

• ADHD (Attention-Deficit/Hyperactivity Disorder)

• Impulse Control Disorders

• Anxiety Disorders

• Depression

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Key Points

• Intellectual disabilities are lifelong.

• They are not diseases and cannot be “cured,” but support, education, and therapy can greatly improve quality of life.

• Many people with ID have strong talents and positive qualities – e.g., acting, art, sport, or excellent interpersonal warmth.

1. What are Intellectual Disabilities according to the DSM-5?
   Intellectual disabilities are when people have a learning level below average before the ages of 18–22. They may struggle with thinking, conceptual, social, and practical skills. Support may come from special education, therapists, or carers.

2. How are intellectual disabilities diagnosed?
   Through testing of intellectual functioning (IQ) and adaptive functioning (daily living skills). The difficulties must begin before the age of 18.

3. What are some common causes?
   Genetic conditions (e.g., Down syndrome), birth complications, illness, injury, or unknown causes.

4. What kind of support might be needed?
   Help with learning, communication, independent living, social skills, and work training.

5. Why is understanding intellectual disabilities important?
   It helps carers and professionals provide better support, reduce stigma, and promote inclusion.