Many individuals have co-existing morbities, compounding their difficulties:
Physical:
- defects of vision and hearing
- cerebral palsy
- difficulty with speech and communication
Epilepsy:
- occurs in 30% of children with severe intellectual developmental disorders
- seizures may be poorly controlled, producing disturbed behaviour or additional brain damage
- anticonvulsant medication may produce side-effects or toxic effects
- social rejection is often increased
Psychiatric disorder:
- occurs in 30% of children with intellectual developmental disorders, threefold higher than the general population
- the incidence of psychiatric disorder increases with the degree of intellectual retardation
- the distribution of disorder (e.g. emotional, antisocial, developmental) is the same in children of average intelligence
The following conditions are more common in patients with intellectual developmental disorders:
- autism
- hyperkinetic syndrome
- stereotyped movements
- pica