1. mental retardation
1.1. levels
1.1.1. severe
1.1.1.1. IQ of 20 to 34
1.1.2. moderate
1.1.2.1. IQ of 35 to 49
1.1.3. mild
1.1.3.1. IQ of 50 to 70
1.1.4. profound
1.1.4.1. IQ below 20
1.2. origins
1.2.1. down syndrome
1.2.1.1. occurs when an abnormality during conception results in an extra twenty-first chromosome
1.2.2. inherited cause
1.2.2.1. fragile X syndrome
1.2.2.2. williams syndrome
1.2.3. environmental causes
1.2.3.1. exposure to German measles
1.2.3.2. alcohol or other toxins before birth
1.2.3.3. oxygen deprivation during birth
1.2.3.4. head injuries
1.2.3.5. brain tumors
1.2.3.6. infectious diseases in childhood
1.2.4. familial
1.2.4.1. 30 to 40 percent in which there is no obvious genetic or environmental causes
1.2.4.2. retardation appears to result from a complex interaction between heredity and environment that researchers are continuing to explore.
2. Giftedness
2.1. high IQs
2.1.1. gifted people can display at least 7 different combinations of the analytic, creative, & practical skills
2.1.2. an extremely high IQ doesn't guarantee special distinction
3. learning disabilities
3.1. dyslexia
3.1.1. difficult to understand the meaning of what they read; sounding out and identifying written words
3.2. dysphasia
3.2.1. difficulty with understanding spoken words or with recalling words
3.3. dysgraphia
3.3.1. problems with writing
3.4. dyscalculia
3.4.1. difficulty with arithmetic