- Intellectual disability (ID), formerly referred to as mental retardation, is a neurodevelopmental disorder characterized by significant limitations in both intellectual functioning and adaptive behavior, which includes the conceptual, social, and practical skills required for everyday life. These limitations must originate during the developmental period, typically before the age of 18.
- Intellectual functioning generally refers to cognitive abilities such as reasoning, problem-solving, planning, abstract thinking, judgment, and learning from experience, commonly measured by standardized intelligence quotient (IQ) tests.
- An individual is typically considered to have an intellectual disability if they score approximately two standard deviations below the mean on an IQ test—usually an IQ of 70 or below—and demonstrate deficits in at least two areas of adaptive functioning. These adaptive behaviors are essential for independent living and may include skills related to communication, self-care, social skills, safety, academic abilities, and occupational functioning. Importantly, diagnosis requires a comprehensive evaluation that looks beyond IQ scores to consider the individual’s ability to function effectively in their environment.
- Intellectual disability is classified into levels of severity—mild, moderate, severe, and profound—based on the degree of impairment in intellectual and adaptive functioning. Most individuals with ID fall into the mild category and can often achieve a degree of independence with proper support. Those with more severe forms may require lifelong assistance and intensive intervention across multiple domains of daily life.
- The causes of intellectual disability are numerous and diverse. Genetic conditions, such as Down syndrome, Fragile X syndrome, and Rett syndrome, are well-known contributors. Prenatal factors, including maternal infections (e.g., rubella, Zika virus), exposure to alcohol or drugs, malnutrition, and environmental toxins can also impair brain development. Complications during birth, such as oxygen deprivation, and postnatal injuries like traumatic brain injury, severe illness, or neglect and abuse can also lead to ID. In many cases, however, the exact cause remains unknown.
- Early diagnosis is crucial for optimizing outcomes. Pediatricians, psychologists, and developmental specialists play a vital role in identifying delays in language, motor, and social development. Once diagnosed, children with intellectual disability can benefit greatly from early intervention services, including speech therapy, occupational therapy, special education, and family support programs. These interventions aim to build skills, maximize independence, and enhance quality of life.
- The educational and social needs of individuals with ID vary considerably depending on the severity of the disability. Many children with mild to moderate ID can attend inclusive schools with appropriate accommodations and support services, such as individualized education programs (IEPs). Others may benefit more from specialized education settings. Transition planning in adolescence is essential to prepare individuals for adult life, including vocational training, employment support, and community living.
- While intellectual disability is a lifelong condition, many individuals can lead meaningful and fulfilling lives when provided with appropriate supports. The level of independence varies, with some living independently, maintaining jobs, and forming relationships, while others may need structured residential care and long-term assistance. Families often play a critical role in caregiving and advocacy, and access to community resources is essential for supporting both the individual and their caregivers.
- In recent years, societal perspectives on intellectual disability have shifted significantly. The disability rights movement has emphasized inclusion, dignity, and autonomy for people with ID. Legal protections in many countries, such as the Americans with Disabilities Act (ADA) and the UN Convention on the Rights of Persons with Disabilities, have reinforced the rights of individuals with intellectual disabilities to access education, healthcare, employment, and public services free from discrimination.
