Intellectual disability (ID), also known as general learning disability, It is defined by an IQ under 70, Intellectual disability is subdivided into syndromic intellectual disability, in which intellectual deficits associated with other medical and behavioural signs and symptoms are present, and non-syndromic intellectual disability, in which intellectual deficits appear without other abnormalities. Down syndrome and fragile X syndrome are examples of syndromic intellectual disabilities.
Intellectual disability affects about 2–3% of the general population. 75 to 90 % of the affected people have mild intellectual disability. About a quarter of cases are caused by a genetic disorder, and about 5% of cases are inherited from a person’s parents. Cases of unknown cause affect about 1million people as of the 2018 census.