The term learning disability covers a variety of clinical presentations, syndromes and underlying pathologies. About 1% of the population have a learning disability and most studies have found that the risk of mental-health problems is higher in people with a learning disability. However, identifying mental health problems in people with a learning disability is difficult. An Australian study used a register of people with learning disabilities and a register of people with mental-health problems to look at people with a 'dual diagnosis' of learning disability and mental illness. The study showed that 31.7% of people with an intellectual disability had a psychiatric disorder, while 1.1% of people with a psychiatric illness had an intellectual disability. Schizophrenia was most closely linked to learning disabilities and 3.7-5.2% of those with intellectual disabilities had co-occuring schizophrenia. Pervasive developmental disorder was much more common among people with 'dual diagnosis' while Down Syndrome was much less common. Individuals with a learning disability and mental health problems were more disabled than those with psychiatric illness alone.
Morgan, Vera A. ... [et al] - Intellectual disability co-occuring with schizophrenia and other psychiatric illness: population-based study British Journal of Psychiatry November 2008, 193(5), 364-372