Module 1: Intellectual Disabilities

Causes of Intellectual Disability

There are many factors that can cause intellectual disability, and in some cases, the cause is not determined. Causes are grouped based on a developmental timeframe into three broad categories.

Prenatal

Prenatal causes occur prior to birth in the developmental period during pregnancy or have a genetic origin.

Causes:

  • Brain malformations
  • Inherited disorders
  • Genetic abnormalities that result into a group of characteristics referred to as syndromes
  • Prenatal exposure to drugs, alcohol, or environmental toxins (teratogens)
  • Exposure to disease

Perinatal

Perinatal causes occur during and around birth.

Causes:

  • Complications during birth
  • Low birthweight
  • Exposure to disease, bacteria, or a virus

Postnatal

Postnatal causes occur after birth.

Causes:

  • Early childhood illnesses such as meningitis and measles
  • Acquired brain injury such as accident, injury, anoxia, and stroke
  • Variety of environmental factors

Severity of Intellectual Disability

Intellectual disability is commonly categorized according to severity: mild, moderate, and severe. The American Psychiatric Association continues the use of these categories in the DSM-V, using adaptive functioning across conceptual, social, and practical skills to determine severity level instead of the previously used IQ scores (APA, 2021).

Mild Intellectual Disability

Adaptive functioning is mildly impacted. This level of disability might not be identified until school-age when difficulties with academics emerge. Most developmental milestones are met, though they could take longer to achieve. Extra time and support could be required for skill development at home and in school. Most people with mild intellectual disabilities develop the skills required to lead independent adult lives.

Moderate Intellectual Disability

Adaptive functioning is moderately impacted. This level of disability is generally noted in the delayed achievement of developmental milestones such as sitting, walking, and talking. Children with moderate intellectual disabilities can take longer and require support to achieve milestones. Children with moderate intellectual disabilities can:

  • Learn basic literacy and numeracy skills
  • Independently access familiar places in the community
  • Make vocational contributions
  • Form meaningful relationships 

Adults with this level of intellectual disability might require ongoing support to live in the community.

Severe Intellectual Disability

Adaptive functioning is severely impacted. This level of disability could be known prior to birth and is identifiable by the level of difficulty in achieving developmental milestones. Most developmental milestones will not be met, and significant support will be required. Many areas of functioning can be impacted, including:

  • Cognition
  • Movement
  • Communication and social skills

Children with a severe intellectual disability, with the right supports, can lead meaningful, contributing lives as adults. Supports for individuals with intellectual disabilities must be specific and individualized to their needs.