Intellectual Disability and Developmental Disorders
What the exam tests
This domain tests definition, developmental assessment, genetic causes, communication and capacity. You must not diagnose intellectual disability from an IQ score alone.
Core rules
- Intellectual disability requires deficits in intellectual function and adaptive behaviour, with onset during the developmental period.
- Severity is based on adaptive functioning, not IQ alone: mild, moderate, severe and profound.
- Common genetic causes include Down syndrome, fragile X syndrome and tuberous sclerosis; prenatal, perinatal and postnatal causes also matter.
- Autism and ADHD commonly co-occur with intellectual disability; assess communication, sensory needs and challenging behaviour.
- Psychiatric illness may present as behaviour change; do not attribute all distress to the disability, known as diagnostic overshadowing.
- Assess capacity in a communication-accessible way; intelligence does not equal capacity.
Worked example
A 10-year-old has a full-scale IQ of 62, adaptive deficits in self-care and social communication, and no regression. This supports mild intellectual disability. The reasoning is that both intellectual and adaptive deficits are present from early development. Look for a cause, screen hearing and vision, assess epilepsy and autism, and plan educational and family support; do not rely on the IQ number alone.
Traps that cost marks
Do not equate intellectual disability with mental illness. Do not miss depression, pain, constipation or abuse behind new aggression. Do not assume incapacity because of a low IQ. Do not overlook dementia in adults with Down syndrome, where decline may present as behaviour change.