Intellectual Disability

Intellectual disability involves problems with general mental abilities that affect functioning in two areas:

• Intellectual functioning (such as learning, problem solving, judgement)
• Adaptive functioning (activities of daily life such as communication and independent living)

The international definition for intellectual disability has three criteria:

• Significant limitations in intelligence (classified as an IQ level of 70 or below)
• 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 are evident in the developmental period (i.e. before the person is aged 18 years)

Intellectual disability affects about one percent of the population, and of those about 85 percent have mild intellectual disability. Males are more likely than females to be diagnosed with intellectual disability.

Some mental health, neurodevelopmental, medical and physical conditions frequently co-occur in individuals with intellectual disability, including cerebral palsy, epilepsy, ADHD, autism spectrum disorder and depression and anxiety disorders. Identifying and diagnosing co-occurring conditions can be challenging, for example recognizing depression in an individual with limited verbal ability. However, accurate diagnosis and treatment are important for a healthy and fulfilling life for any individual.

What Are the Most Common Causes?

The most common causes of intellectual disabilities are:

• Genetic conditions. Sometimes an intellectual disability is caused by abnormal genes inherited from parents, errors when genes combine, or other reasons. Examples of genetic conditions are Down syndrome, Fragile X syndrome, and phenylketonuria (PKU).

• Complications during pregnancy. An intellectual disability can result when the baby does not develop inside the mother properly. For example, there may be a problem with the way the baby’s cells divide. A woman who drinks alcohol or gets an infection like rubella during pregnancy may also have a baby with an intellectual disability.

• Problems during birth. If there are complications during labor and birth, such as a baby not getting enough oxygen, he or she may have an intellectual disability.

• Diseases or toxic exposure. Diseases like whooping cough, the measles, or meningitis can cause intellectual disabilities. They can also be caused by extreme malnutrition, not getting appropriate medical care, or by being exposed to poisons like lead or mercury.