Tetrasomy X and pentasomy X syndrome affect a small number of girls worldwide, while boys may be affected by 49, XXXXY, or 49, XYYYY. 47, XYY is not associated with significantly lowered IQ though affected individuals may have slightly lower IQs than non-affected siblings on average. Problems during pregnancy. Intellectual disability can result when the fetus does not develop properly. For example, there may be a problem with the way the fetuss cells divide as it grows. A pregnant woman who drinks alcohol (see fetal alcohol spectrum disorder) or gets an infection like rubella during pregnancy may also have a baby with an intellectual disability. Problems at birth. If a baby has problems during labor and birth, such as not getting enough oxygen, he or she may have a developmental disability due to brain damage. The group of proteins known as histones have an essential part in gene regulation, and sometimes these proteins becomes modified and are prevented from working properly. When the genes responsible for the development of neurons are affected, it affects the brain and behavior in the individual. Exposure to certain types of disease or toxins. Diseases like whooping cough, measles, or meningitis can cause intellectual disability if medical care is delayed or inadequate. Exposure to poisons like lead or mercury may also affect mental ability. Iodine deficiency, affecting approximately 2 billion people worldwide, is the leading preventable cause of intellectual disability in areas of the developing world where iodine deficiency is endemic.
It is not specific to congenital disorders such as Down syndrome.The American Association on Mental Retardation changed its name to the American Association on Intellectual and Developmental Disabilities (AAIDD) in 2007, and soon thereafter changed the names of its scholarly journals to reflect the term "intellectual disability". In 2010, the AAIDD released its 11th edition of its terminology and classification manual, which also used the term intellectual disability. United Kingdom
In the UK, mental handicap had become the common medical term, replacing mental subnormality in Scotland and mental deficiency in England and Wales, until Stephen Dorrell, Secretary of State for Health for the United Kingdom from 1995 to 1997, changed the NHSs designation to learning disability. The new term is not yet widely understood, and is often taken to refer to problems affecting schoolwork (the American usage), which are known in the UK as "learning difficulties". British social workers may use "learning difficulty" to refer to both people with intellectual disability and those with conditions such as dyslexia.