Intellectual Disability (ID) (formerly known as mental retardation) is defined in the DSM-5 (Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition) as a neurodevelopmental disorder. It is characterized by deficits in intellectual functioning and adaptive functioning, which result in impairments in conceptual, social, and practical skills. The condition arises during the developmental period, typically before the age of 18.

DSM-5 Diagnostic Criteria for Intellectual Disability (ID)

The diagnosis of Intellectual Disability requires meeting the following three criteria:

A. Deficits in intellectual functioning:

• This refers to impairments in reasoning, problem-solving, planning, abstract thinking, judgment, academic learning, and learning from experience.
• These deficits are confirmed by both:
  • Clinical assessment, and
  • Standardized intelligence testing (e.g., IQ score typically below 70-75).

B. Deficits in adaptive functioning:

• These impairments result in a failure to meet developmental and sociocultural standards for personal independence and social responsibility.
• Without ongoing support, the deficits limit functioning in one or more activities of daily life, such as:
  • Communication
  • Social participation
  • Independent living across multiple environments (e.g., home, school, work, community).
• The deficits affect the following domains:
  1. Conceptual domain: Skills in language, reading, writing, math, reasoning, knowledge, and memory.
  2. Social domain: Empathy, social judgment, interpersonal communication skills, and the ability to make and maintain friendships.
  3. Practical domain: Self-management skills in personal care, job responsibilities, money management, recreation, and organizing school and work tasks.

C. Onset during the developmental period:

• The intellectual and adaptive deficits must begin during childhood or adolescence, typically before the age of 18.

Severity Levels of Intellectual Disability

The DSM-5 categorizes the severity of ID based on the level of impairment in adaptive functioning, rather than IQ score alone. The severity levels are determined by the impact of the intellectual and adaptive deficits on the individual’s daily life and functioning in different environments.

1. Mild Intellectual Disability:

• Conceptual domain: Individuals may have difficulty with academic skills, especially in reading, writing, and math. Adults may need assistance with complex daily tasks (e.g., managing finances).
• Social domain: Individuals can engage in social relationships but may have difficulty with complex social interactions. They may show immature behavior and have difficulty regulating emotions.
• Practical domain: Individuals can generally care for themselves, but they may need support in complex tasks such as making healthcare or legal decisions.

2. Moderate Intellectual Disability:

• Conceptual domain: Academic skills typically develop slowly, and the individual may not progress beyond an elementary school level. Ongoing support is required for daily life tasks like work and personal care.
• Social domain: Social communication is more limited, and individuals may have difficulty with friendships and social judgments.
• Practical domain: Individuals can perform personal care independently but need help with more complex tasks and decision-making. They may work in structured settings with supervision.

3. Severe Intellectual Disability:

• Conceptual domain: There is little understanding of written language or numerical concepts. Caretakers help with problem-solving throughout life.
• Social domain: Speech and language are limited, and social interactions are typically focused on concrete needs. They may require close supervision in social settings.
• Practical domain: Individuals need assistance with most daily activities, including personal hygiene and safety. They require supervision and support throughout their lives.

4. Profound Intellectual Disability:

• Conceptual domain: Individuals may have very limited understanding of symbolic concepts or skills. They may be able to participate in simple activities that involve matching or sorting.
• Social domain: Communication is often nonverbal and focused on basic needs. Relationships are often based on emotional responses to caregivers.
• Practical domain: Individuals require constant support and supervision for all aspects of daily living, including eating, bathing, and dressing. They need constant supervision to ensure safety.

Key Features of Intellectual Disability

• Heterogeneity: The severity and presentation of ID vary greatly between individuals.
• Lifespan implications: Intellectual disability affects functioning throughout the lifespan, but early intervention, education, and support can improve outcomes.
• Comorbid conditions: Many individuals with intellectual disabilities may also have other mental health conditions, such as anxiety, depression, or autism spectrum disorder.

Assessment and Diagnosis

• Standardized intelligence tests (e.g., Wechsler Intelligence Scales, Stanford-Binet) are used to assess intellectual functioning.
• Adaptive functioning is typically evaluated through interviews, standardized scales (e.g., Vineland Adaptive Behavior Scales), and observations in multiple environments (e.g., home, school, work).

The focus in DSM-5 is on adaptive functioning as the primary determinant of the severity of intellectual disability, as this better reflects the individual’s capacity to cope with everyday demands, rather than relying solely on an IQ score.

Reference:

American Psychiatric Association, DSM-5 Task Force. (2013). Diagnostic and statistical manual of mental disorders: DSM-5™ (5th ed.). American Psychiatric Publishing, Inc.. https://doi.org/10.1176/appi.books.9780890425596

DSM Cover image source:

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