Intellectual disability (ID) is a neurodevelopmental condition that impacts an individual’s functioning in two key areas: cognitive and adaptive. Cognitive functioning encompasses abilities like learning, problem-solving, and judgment, while adaptive functioning relates to everyday life skills, including communication and social participation. Crucially, these deficits in both intellectual and adaptive functioning must emerge during the developmental period, typically before the age of 18, to warrant a Diagnosis Of Intellectual Disability.
Approximately 1% of the global population is affected by intellectual disability, with the majority, around 85%, experiencing mild ID. In higher-income countries, the prevalence among children is slightly higher, ranging from 2% to 3%. Understanding the diagnostic process is paramount for accessing appropriate support and improving outcomes for individuals with intellectual disability.
How is Intellectual Disability Diagnosed?
The diagnosis of intellectual disability hinges on identifying significant limitations in both intellectual and adaptive functioning. This is not solely based on a single test score but involves a comprehensive evaluation.
Assessing Intellectual Functioning
Intellectual functioning is evaluated using individually administered, psychometrically valid, and culturally appropriate intelligence tests. While a specific IQ score is no longer the sole determinant, standardized testing remains a crucial component of the diagnostic process. Historically, an IQ score of around 70 to 75 (approximately two standard deviations below the mean) has been indicative of a significant limitation in intellectual functioning. However, it’s essential to interpret IQ scores cautiously and within the broader context of an individual’s overall mental abilities. Subtest scores can vary significantly, meaning the full-scale IQ score might not always accurately reflect overall intellectual capacity. Therefore, clinical judgment plays a vital role in interpreting IQ test results.
Delving Deeper: What Constitutes Intellectual Functioning? Intellectual functioning is a multifaceted concept that encompasses intelligence, the abilities measured by standardized intelligence tests, and the understanding that intellectual capacity is influenced by various human functioning dimensions and support systems. While IQ tests have been traditionally used to measure cognitive or intellectual functioning, with a score below 70 often considered a benchmark for Intellectual Disability diagnosis, current clinical practice also necessitates a score of two or more standard deviations below the population norm (roughly below the 2nd/3rd percentile) on standardized adaptive skills measures, such as the Vineland Adaptive Behavior Scales.
Evaluating Adaptive Behavior
Adaptive behavior refers to the collection of conceptual, social, and practical skills learned and applied by individuals in their daily lives. These skills are essential for everyday functioning and are categorized into three core areas:
Key Areas of Adaptive Functioning:
- Conceptual Skills: These encompass abilities related to language, reading, writing, mathematics, reasoning, knowledge, and memory.
- Social Skills: This area includes empathy, social judgment, communication skills, the capacity to follow rules, and the ability to form and maintain friendships.
- Practical Skills: Practical skills relate to independence in daily living tasks such as personal care, job responsibilities, managing finances, engaging in recreation, and organizing school or work assignments.
Adaptive functioning is assessed using standardized measures administered directly to the individual and through interviews with informants such as family members, teachers, and caregivers who are familiar with the individual’s typical performance in daily life.
Age of Onset: A Critical Factor
The age of onset is the third essential criterion for diagnosing intellectual disability. This criterion establishes the timeframe within which ID must originate or first manifest. The American Association on Intellectual and Developmental Disabilities (AAIDD) guidelines specify an age of onset “before the individual attains age 22,” reflecting research indicating that significant brain development continues into the early twenties.
Often, the clinical signs and symptoms of intellectual disability are first recognized during infancy and childhood. Intellectual disability is further classified based on severity as mild (the most common category), moderate, severe, or profound.
Uncovering the Causes of Intellectual Disability
Intellectual disability is not a disease itself but rather a condition with diverse underlying causes. In many cases, ID can be linked to genetic syndromes such as Down syndrome or Fragile X syndrome. It can also develop as a consequence of illnesses like meningitis, whooping cough, or measles, or result from head trauma during childhood or exposure to toxins like lead or mercury. Other contributing factors can include brain malformations, maternal illnesses during pregnancy, and environmental influences such as alcohol, drugs, or other toxins. Furthermore, complications during labor and delivery, infections during pregnancy, and birth-related issues like oxygen deprivation can also play a role in the development of intellectual disability.
Management and Support Strategies
Intellectual disability is typically a lifelong condition. However, early and consistent intervention can significantly improve an individual’s functioning and enable them to thrive throughout their lives. Underlying medical or genetic conditions, as well as co-occurring conditions, can add complexity to the lives of individuals with intellectual disability, requiring a holistic approach to management.
Once a diagnosis of intellectual disability is established, the focus shifts to understanding the individual’s strengths and needs, and identifying the necessary supports to facilitate their optimal functioning at home, in educational or work settings, and within the community.
A wide array of treatments and support services can be beneficial for individuals with intellectual disabilities and their families, promoting community inclusion and enhancing quality of life. These services can include:
- Treatment for associated medical complications.
- Routine preventive medical care.
- Management of co-occurring medical and mental health conditions.
- Interventions for challenging behaviors.
- Rehabilitation services.
- Early intervention programs for infants and toddlers.
- Special education services.
- Family support services, such as respite care and support groups.
- Transition services to facilitate the shift from childhood to adulthood.
- Vocational training programs.
- Day programs for adults.
- Housing and residential options.
- Case management services to coordinate care.
Legislation like the Individuals with Disabilities Education Act (IDEA) in the United States mandates early intervention services for infants and toddlers with disabilities. IDEA also ensures that free special education and related services are available to all eligible children with disabilities, including intellectual disability.
Support can also come from various sources, including family, friends, colleagues, community members, schools, medical teams, and service systems. Job coaching, for example, is a valuable support provided by service systems. With appropriate and consistent support, individuals with intellectual disabilities are capable of leading fulfilling and productive lives, contributing meaningfully to society.
A formal diagnosis of intellectual disability often opens doors to essential services and legal protections, such as access to special education and home and community-based services. The AAIDD emphasizes that the primary goal of evaluating individuals for intellectual disability is to identify and implement the supports and services necessary for them to flourish in their communities throughout their lives.
Practical Tips for Parents and Caregivers
Navigating the journey of raising a child with intellectual disability can be challenging yet rewarding. Here are some helpful tips for parents:
- Seek Support and Information: Don’t hesitate to ask for help and actively learn about your child’s specific disability.
- Connect with Others: Join support groups and connect with other parents of children with disabilities to share experiences and gain valuable insights.
- Practice Patience: Understand that learning may take more time for your child, and celebrate every milestone, no matter how small.
- Foster Independence and Responsibility: Encourage your child’s independence and assign age-appropriate responsibilities to build their self-esteem and skills.
- Advocate for Education: Educate yourself about the educational services your child is entitled to and advocate for their needs within the school system.
- Know Your Rights: Familiarize yourself with the laws and regulations designed to support individuals with disabilities and ensure your child’s rights are protected.
- Explore Community Opportunities: Look for social, recreational, and sports activities in your community, such as organizations like Best Buddies or Special Olympics, to promote social inclusion and engagement.
Co-occurring Conditions
It’s important to recognize that individuals with intellectual disability frequently experience co-occurring mental health, neurodevelopmental, medical, and physical conditions. These can include autism spectrum disorder, cerebral palsy, epilepsy, attention-deficit hyperactivity disorder (ADHD), impulse control disorders, depression, and anxiety disorders. Identifying and accurately diagnosing these co-occurring conditions can be complex, particularly when recognizing conditions like depression in individuals with limited verbal abilities. Family caregivers play a crucial role in observing subtle changes in behavior and well-being. Accurate diagnosis and appropriate treatment of both intellectual disability and any co-occurring conditions are essential for promoting a healthy and fulfilling life for every individual.
References:
- The term intellectual disability used in DSM-5-TR replaces “mental retardation” used previously.
- The majority of people, 68%, have IQ scores between 85 and 115.
- American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition-Text Revision. Arlington, VA: APA Publishing; 2022.
- Totsika V, Liew A, Absoud M, Adnams C, Emerson E. Mental health problems in children with intellectual disability. Lancet Child Adolesc Health. 2022 Jun;6(6):432-444. doi: 10.1016/S2352-4642(22)00067-0.
- Schalock, R. L., Luckasson, R., and Tassé, M. J. 2021. Twenty questions and answers regarding the 12th edition of the AAIDD manual: Intellectual disability: definition, diagnosis, classification, and systems of supports. American Association on Intellectual and Developmental Disabilities.
- Schalock, Robert L., et al. 2021. Intellectual Disability: Definition, Diagnosis, Classification, and Systems of Supports. 12th edition., American Association on Intellectual and Developmental Disabilities (AAIDD). ISBN-13: 978-0-9983983-6
- Patel DR, Cabral MD, Ho A, Merrick J. A clinical primer on intellectual disability. Transl Pediatr. 2020 Feb;9(Suppl 1):S23-S35. doi: 10.21037/tp.2020.02.02.
Physician Review:
Rubí E. Luna, M.D. UCLA Semel Institute for Neuroscience and Human Child and Adolescent Psychiatry Fellow, PGY-5
March 2024
