The Genetics of Mental Retardation

Mental retardation(MR) was defined by the World Health Organisation as an intelligent quotient (IQ)<70 that is accompanied by adaptive limitations in two or more key skills areas, before the age of 18. General intellectual functioning is expressed by IQ. Typically, in chil‐ dren younger than 5 years old who present delays in the attainment of developmental mile‐ stones at the expected age, the term of "developmental delay" is used. Also, developmental delay is used before the age of 5,when IQ testing is reliable and valid and it takes into con‐ sideration learning and adaptive deficits which predict later intellectual disability.

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