The point prevalence of a major depressive illness in people with learning disability is between 2 and 7%, which means that depression can be twice as common in this group as in the general population (Reference PrasherPrasher, 1999).

Collishaw et al (Reference Collishaw, Maughan and Pickles2004) present strong evidence for directing strategies of primary prevention towards socio-economic deprivation and ill health in people with mild learning disabilities. However, these results should be viewed with caution as the study did not control for certain important factors. Certain groups of people with learning disability are shown to be at a risk of developing a depressive illness, for example those with Down's syndrome, fragile-X syndrome or epilepsy (Reference PrasherPrasher, 1999).

Down's syndrome and fragile-X syndrome are among the most common genetic causes of learning disabilities, and epilepsy is 10 times more common in people with mild learning disability than in the general population (Reference Bird and RussellBird, 1997).

This implies that factors other than socio-economic deprivation could have contributed to the depressed mood in those with mild learning disability.