Intellectual Disability diagnosis may occur based
on many different factors such as:


  • Prenatal
    Chromosome disorders or disorders of brain formation before birth.  Down Syndrome
    is the most  common.  An individual with this disorder has an extra copy of Chromosome 21.
  • Perinatal
    During the birth process, premature birth or birth injury.
  • Postnatal
    Traumatic brain injury or infection after birth.

Risk Factors

  • Biomedical factors
    Genetic disorders or lack of nutrition before birth.
  • Social factors
    Lack of social stimulation or adult responsiveness.
  • Behavioral factors
    Dangerous activities during pregnancy, such as substance abuse.
  • Educational factors
    Lack of educational supports to promote development and adaptive skills

An intellectual disability is often diagnosed early in an individual’s life.
Two major characteristics are required in order to diagnose an
intellectual disability.

1.  Limitations in intellectual functioning:

  • Intelligence Quotient (IQ) score that is two or more standard deviations below the mean.
    55 – 70 is termed a mild Intellectual Disability.
  • Moderate Intellectual Disability is an IQ score of 40 – 55.
  • Severe Intellectual Disability is an IQ score of 25 – 40.
  • Profound Intellectual Disability is an IQ score of 25 or less.Additional challenges may include difficulty with short-term, working memory, and generalizing
    or applying skills to many different environments.

2.  Limitations in adaptive behavior:

An individual needs to demonstrate a lack of adaptive skills in at least one of the three domains of adaptive behavior.

  1. Conceptual skills
    Difficulty with language (expressive and receptive), reading, writing, money, and self-awareness
    or direction.
  2. Social skills
    Difficulty making and keeping age-appropriate relationships and following rules.  May be more susceptible to negative influences from others.
  3. Practical skills
    Difficulty with daily living, work skills, leisure skills, and community skills.