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.
A hypotonic-hyporesponsive episode (HHE) is defined as sudden onset of poor muscle tone, reduced consciousness, and pale or bluish skin occurring within 48 hours after vaccination, most commonly pertussis vaccination. An HHE is estimated to occur after 1 in 4,762 to 1 in 1,408 doses of whole cell pertussis vaccine, and after 1 in 14,286 to 1 in 2,778 doses of acellular pertussis vaccine. == References ==