What is the cause of mental retardation?
There are various known causes of mental retardation, including genetic disorders, maternal infections, psychosocial conditions, drug exposure, and environmental chemical exposure. The established risk factors for MR include: 
- Various genetic disorders (e.g. Down’s Syndrome, phenylketonuria)
- Certain maternal infections during pregnancy (e.g. rubella)
- Mother who abuses substances such as alcohol during pregnancy
- Certain psychosocial conditions (e.g. problems with caregiving, low socioeconomic status, low parental education)
- Maternal exposure to various drugs (e.g. thalidomide, valproic acid)
- Maternal exposure to environmental chemicals (discussed in detail later)