Behavioural phenotypes and mental disorders

Genetic disorders account for a sizeable proportion of learning disabilities. Several disorders are associated with mental ill-health. The commonest examples of psychiatric morbidity include psychosis, depression and dementia. Here, three examples of chromosomal abnormalities that have significant research evidence are used to discuss the origins and management of mental disorders. Adults with Down syndrome may suffer from mood disorders and dementia, which has a prevalence rate of 32% by 59 years of age. Personality changes and behavioural disorders can signal the onset of dementia. Prader–Willi syndrome (PWS) has a complex genetic aetiology. A characteristic behavioural phenotype has been described for the syndrome, which includes psychiatric and psychological manifestations. PWS has been found to be associated with affective disorder. People with fragile X syndrome–the most common identifiable cause of learning disabilities–experience a wide range of developmental and psychological challenges throughout their lifespan. In all three syndromes, understanding of the endophenotypic neuropsychological difficulties facilitates the development of rational and, where possible, syndrome-specific supports and therapies.