Mental retardation

There are four levels of mental retardation - mild, moderate, severe, and profound. Based on the 1990 U.S. Census, an estimated 6.2 to 7.5 million people have mental retardation. Causes of mental retardation range from genetic disorders to lead poisoning, but The Arc states that the three major causes are Down Syndrome, Fetal Alcohol Syndrome, and Fragile-X.
Down Syndrome - Down Syndrome, the most common cause of mental retardation, is a condition caused by a chromosomal abnormality in which, for some unexplained reason, cell development results in 47 instead of 46 chromosomes. This extra chromosome affects the orderly development of the brain and body. Fetal Alcohol Syndrome - Fetal Alcohol Syndrome (FAS) is the name given to a group of physical and mental birth defects that are the direct result of a woman's drinking alcohol during pregnancy. These mental and physical birth defects can include mental retardation, growth deficiencies, central nervous system dysfunction, craniofacial...