In order to be considered mentally retarded, you must have an IQ below 75, have
significant limitations in two or more adaptive skill areas, and the condition
is present from childhood (defined as age 18 or younger). People can be mentally
retarded as all different levels. About 78% of mentally retarded people will
only be a little slower than the average person, while in others it is very
apparent (Arc of New Jersey). There are many causes of mental retardation. One
cause of mental retardation is of genetic conditions. That includes; abnormal
gene mixes from parents, errors when genes combine, overexposure to x-rays, and
many more reasons. More than 500 genetic diseases are associated with mental
retardation. Down Syndrome is an example of a chromosomal disorder (Mental
Retardation Issues). Chromosomal disorders occur every once in a while, and are
caused by too many or too few chromosomes in the restructure of the chromosomes
(The Arc of New Jersey). Another cause is problems during pregnancy. It could
happen if the mother drinks or does drugs while pregnant with the baby. Other
risks include malnutrition, certain environmental contaminants, and the mother
could get ill during the pregnancy. Pregnant women who are infected with HIV may
pass it on to their child. Also very stressful and physical pregnancies and
births can cause damage to a child’s brain (Introduction to Mental
Retardation). Mental Retardation also occurs frequently after birth. Childhood
diseases such as big coughs, chicken pox, measles, and hip disease, which may
lead to meningitis and encephalitis, can damage the brain, as can accidents such
as being hit in the head, near drowning situations, and most other accidents
involving the head. Another that can be harmful to a child mentally is
environmental fumes, lead, mercury, and other dangerous toxins (Introduction to
An American History of Mental Retardation).

BibliographyIntroduction to An American History of Mental Retardation. 3-28-00. http://member.aol.com/MRandDD/introhx.htm.
Introduction to Mental Retardation. 2-25-00. http://thearc.org/faqs/mrqa.html
Mental Retardation Issues. 2-27-00. http://members.amaonline.com/nrogers/mr.htm
The Arc of New Jersey. What is MR. 2-27-00. http://www.arcnj.org/html/what_is_mr.html