A condition of arrested or incomplete development of the mind, which is especially characterised by impairment of skills, manifested during the developmental period, which contribute to the overall level of intelligence, i.e. cognitive, language, motor, and social abilities

Aetiology

Co-morbidities

• People with ID are 3 x more likely to experience another psychiatric disorder than the general population

Clinical features

Severity of ID

Borderline ID - IQ 70-84

• Mental age 12 to under 15 years

Mild ID - IQ 50-69

• Mental age 9 to under 12 years
• Most common
• Delayed speech - able to use everyday speech
• Full independence - self care, practical and domestic skills
• Difficulties in reading and writing
• Capable of unskilled or semi-skilled work
• Problems if social or emotional immaturity
• Rarely organic aetiology

Moderate ID - IQ 35-49

• Mental age 6 to under 9 years