Mental Retardation is a condition that affects 1-3% of the population, in which a person has a below-average intellectual function and a lack of skills nessecary for everyday living.  If someone's IQ score is below 70, they are categorized as having an intellectual disability or mental retardation.  Symptoms include struggling in school, decreased learning ability, lack of curiosity, quietness, and infantile behavior.  Causes of mental retardation include trauma, infection, chromosomal abnormalities, genetic abnormalities, toxins, nutritional deficits, and environment.  However, most cases do not have a specific cause.  Treatment methods are special education and training. Cases can be diagnosed as mild, moderate, severe, or profound. The map below shows mental retardation rates by state in the US.