Intellectual disability (ID), also called intellectual development disorder (IDD) or general learning disability, and formerly known as mental retardation (MR) is a generalized neurodevelopmental disorder characterized by significantly impaired intellectual and adaptive functioning. It is defined by an IQ score below 70 in addition to deficits in two or more behaviors that affect every day, general living.
Pathophysiology: Sometimes disability is caused by abnormal genes inherited from parents, errors when genes combine, or other reasons eg. Down syndrome, Klinefelter's syndrome, Fragile X syndrome (common among boys), neurofibromatosis, congenital hypothyroidism. Intellectual disability can result when the fetus does not develop properly.
Diagnosis: The three criteria must be met for a diagnosis of intellectual disability: deficits in general mental abilities, significant limitations in one or more areas of adaptive behavior across multiple environments and evidence that the limitations became apparent in childhood or adolescence. In general, people with intellectual disability have an IQ below 70, but clinical discretion may be necessary for individuals who have a somewhat higher IQ but severe impairment in adaptive functioning.
The proportion of the population who have had a disorder in the last 12 months ranges from approximately 10 per cent to 33 per cent. The highest international figures are from the most reputable international studies, NCR and NEMESIS. More women than men suffer from mental illness, but the gender differences vary between the different types of disorders. Eating disorders occur almost exclusively among women, and there is also a much higher incidence of anxiety and depression among women than among men.