There are many different possible causes of mental retardation, otherwise referred to as impaired mental development, impaired intellectual development, impaired social development, impaired...
Could be a number of things....
1. Enviromental Toxins
2. In Utero Drug and Alcohol Exposure
3. Malnutrition
4. Brain Damage (Head Injury)
5. Poverty
6. In Utero Exposure to Diabetes
7....
Hyperthyroidism, whooping cough, chickenpox, measles, and Hib disease (a bacterial infection) may cause mental retardation if they are not treated adequately.