Information about intellectual disability, diagnosis, causes, effects and support for people with intellectual disability.
About intellectual disability
Intellectual disability is a developmental disorder. People with intellectual disability have significantly more difficulty than others in learning new things, understanding concepts, solving problems, concentrating and remembering. Consequently, they require extra support to learn and achieve their full potential.
The international definition of intellectual disability has three criteria:
- significant limitations in intelligence—that is an intelligence quotient (IQ) of about 70 or less as measured on a standardised intellectual assessment test
- significant limitations in the skills needed to live and work in the community, including difficulties with communication, self-care, social skills, safety and self-direction
- limitations in intelligence and living skills that are evident before the person is 18 years of age.
All three criteria must be present for a person to be considered as having intellectual disability.
For some people, intellectual disability occurs alongside other disabilities (for example, sensory impairment, physical impairment and/or medical conditions). Some people may have dual disability—that is intellectual disability and mental illness. These other disabilities and conditions are not a result of intellectual disability, but are issues to be considered when supporting a person with intellectual disability.
A formal assessment by a psychologist or other appropriately qualified professional is required to diagnose intellectual disability. An assessment of the person's living skills may also be required. This is usually done by interviewing a parent, teacher or someone else who knows the person well.
Causes of intellectual disability
In many cases the reasons for a person's intellectual disability are not known or cannot be determined. However, some of the most common known causes are:
- genetic conditions (for example, Down syndrome, fragile X syndrome or Rhett syndrome)
- problems during pregnancy (for example, infections or exposure to toxins)
- problems at birth (for example, not getting enough oxygen)
- health problems (for example, whooping cough, measles or meningitis)
- environmental factors (for example, extreme malnutrition, inadequate medical care or exposure to poisons such as lead or mercury).
How many people have intellectual disability?
About one per cent of the population is thought to have intellectual disability. Approximately 6500 people are registered in South Australia with Disability SA as having intellectual disability.
Effects of intellectual disability
Intellectual disability cannot be cured but support can help people with intellectual disability to achieve their potential and lead happy, fulfilling lives.
Some people will be mildly affected in their ability to learn new information and skills. Others may be moderately to severely affected. Early intervention, education, training and support all contribute to people with intellectual disability leading full and satisfying lives.
Support for people with intellectual disability
Find out about more about supports available for people with intellectual disability and how to access them on our main pages:
Preschool children with disability
School-aged children with disability
Adolescents with disability
Adults with disability
Ageing with disability
Aboriginal people with disability
The following approved organisations also specialise in information and support for people with intellectual disability. You may be able to book in by calling them directly (there may be fees) or they will advise you where to go for a referral.
Individual support to people with intellectual disabilities to achieve full community inclusion.
Provides on-job and accredited training, employment, residential and recreational opportunities for people with disability.
Down Syndrome Society of SA Inc
Provides support and services to people with Down syndrome and their families.
Support for people with intellectual disabilities, including accommodation support, skills development, employment support and recreation.
Training and employment support for people with intellectual disabilities.
Child and Youth Health
see intellectual disability
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