CHAPTER 6
MENTAL RETARDATION: ETIOLOGY AND PREVENTATIVE EFFORTS
Chapter Outline
I. Terminology
II. Genetic Disorders
III. Genetic Transmission
A. Dominant Transmission
B. Recessive Transmission
IV. Chromosomal Deviations
A. Down Syndrome
B. Prader-Willi Syndrome
C. Williams Syndrome
D. Sex Chromosomal Differences
V. Cranial Malformations
VI. Other Congenital Factors
A. Maternal Disorders
IX. Prevention
A. Preconception
B. During Gestation
C. At Delivery
D. Early Childhood
Key Terms
amniocentesis
autism
autosomes
chromosomes
deletion
dominant inheritance
Down syndrome
fetal alcohol syndrome
fragile X syndrome
genes
genetics
neurofibromatosis
nondisjunction
phenylketonuria (PKU)
polygenetic inheritance
Prader-Willi syndrome
recessive inheritance
Tay Sach’s
teratogens
translocation
trisomy
Chapter Objectives
Upon completion of this chapter the student will be able to:
1. provide an overview of causation.
2. discuss the basic principles of genetics.
Suggested Activities
1. Invite a genetic counselor to speak to the class.
2. Invite a qualified medical doctor or nurse to speak to the class about different
medications, prescribed and unprescribed, and the affects these medications can have on
a fetus.
4. Contact centers for women who abuse drugs or alcohol and obtain pamphlets and other
literature on how to prevent or treat such disorders. Create a bulletin board using the
materials that you collected.
Evaluation Questions
Multiple Choice
1. In what percentage of all cases can the causes of intellectual disabilities be specified?
A. 5%
B. 20%
C. 30%
D. 50%
2. Traditionally causes of mental retardation and related developmental disorders have been
divided into how many categories?
A. 2
B. 5
C. 7
D. 10
3. Why are mild cases of intellectual disabilities less likely to have an identifiable cause than
severe cases?
A. biological causes are more prevalent among individuals with severe intellectual
disabilities and are easier to determine
B. mild mental retardation is usually the result of multiple unspecifiable
environmental events
C. a & b
D. none of the above
4. J. Langdon Down originally ascribed the term mongolism to the condition now known as
Down syndrome because
A. he observed inaccurately that one frequent characteristic of the
syndrome was facial similarities to Asians.
B. the term mongol means a variety of associated conditions.
C. most cases of the syndrome came from the country of Mongolia.
D. he considered the term mongoloid less stigmatizing than other terms in use at that
time.
5. Neurofibromatosis, the disorder that is characterized by light brown patches on the skin, and
fibrous swellings or tumors growing on the nerves producing severe physical deformities
affects approximately
A. 1 in 6000 newborns
B. 1 in 3000 newborns
C. 1 in 1000 newborns
D. 1 in 500 newborns
6. A condition characterized by a saclike mass on the spinal cord containing membrane tissue of
the central nervous system and cerebrospinal fluid but no spinal nerves on the spinal cord is
A. hydrocephalus
B. phenylketonuria (PKU)
C. fragile X syndrome
D. myelomeningocele
7. The study of heredity and variation is called
A. chromosomes
B. trisomy
C. genes
D. genetics
8. How can the Human Genome Project address intellectual disabilities?
A. through research on gene mapping and DNA sequencing
B. uniparental disomy
C. meiosis
D. through the study of environmental factors
9. What is the relationship between Trisomy 21 and Mosaic Down syndrome?
A. both disorders encounter abnormalities on chromosome 21
B. each disorder makes up 50% of Down syndrome cases
C. both disorders are rare among individuals with intellectual disabilities
D. both disorders are a form of Down syndrome
10. Threadlike bodies containing genes occupying specific loci are
A. teratogens
B. autosomes
C. genes
D. chromosomes
11. How many pairs of chromosomes are there in a cell?
A. 2
B. 23
C. 25
D. 44
12. Twenty-two matched pairs of chromosomes are
A. genetics
B. dominant inheritance
C. recessive inheritance
D. autosomes
13. How many sex chromosomes are there?
A. 2
B. 23
C. 25
D. 44
14. Genes carrying the same trait are called
A. heterozygous.
B. homozygous.
C. recessive.
D. dominant.
15. If both parents carry the same trait, the child’s gene will be described as
A. heterozygous.
B. homozygous.
C. recessive.
D. dominant.
16. An individual gene that has control or can mask the other gene in the pair is called
A. recessive inheritance
B. dominant inheritance
C. deletion
D. translocation
17. In what case would a recessive gene be expressed?
A. in a child with blue eyes
B. in several disorders capable of producing severe disabilities
C. in such health impairments as sickle-cell anemia and cystic fibrosis
D. all of the above
18. An inherited metabolic disease resulting from the absence of an enzyme for digestion
which causes a toxic buildup of substances in the blood and urine is called
A. Fragile X
B. Phenylketonuria (PKU)
C. Tay-Sach’s Disease
D. Down Syndrome
19. The interaction of multiple genes and networks which influences individual
intellectual functioning is called
A. Human Genome Project
B. mosaicism
C. polygenetic inheritance
D. meiosis
20. Which of the following is more likely to occur?
A. a chromosomal disorder occurring in a child when the mother is over age 35
B. a chromosomal disorder occurring in a child when the mother is over age 32
C. a chromosomal disorder occurring in a child when the mother is under age 20
D. none of the above
21. The use of abnormal chromosome arrangements present from conception but most
often not the product of hereditary exchange is known as
A. innate
B. autosomes
C. mosaicism
D. mutation
22. The division and pairing of gametes to form the genetic formation for an embryo is
A. nondisjunction
B. chromosomes
C. mosaicism
D. meiosis
23. The most common cause of Down syndrome is
A. inheritance.
B. mosaicism.
C. translocation.
D. Trisomy 21.
24. The failure of one pair of chromosomes to split correctly at meiosis resulting in a
trisomy is
A. deletion
B. homozygous
C. nondisjunction
D. mosaicism
25. The exchange of a fragment of chromosomal material within the same chromosome
is called
A. genetics
B. variable expressivity
C. translocation
D. uniparental disomy
26. The chromosomal abnormality that has been associated with mild to moderate retardation,
learning disabilities, and insatiable appetite is
A. Fragile X syndrome.
B. Klinefelter syndrome.
C. Prader-Willi syndrome.
D. Turner syndrome.
27. A disorder resulting from blockage of cerebrospinal fluid in the cranial cavity that causes
an enlarged head and undue pressure on the brain is termed
A. anoxia
B. Tay Sach’s
C. hydrocephalus
D. Prader-Willi syndrome
28. Which of the following gestation periods is most likely to be associated with birth
defects?
A. 24–28 weeks.
B. 37–41 weeks.
C. 42–46 weeks.
D. 52 weeks.
29. Oxygen deprivation severe enough to cause permanent brain damage and retardation
is called.
A. anoxia
B. hydrocephalous
C. deletion
D. amniocentesis
30. An intervention that assists a child who has a disability is a
A. pre-natal prevention.
B. primary prevention.
C. secondary prevention.
D. tertiary prevention
True or False
Directions: If the statement is true, simply mark True. If the statement is false, mark
False and rewrite the statement so that it is true.
1. Approximately10% of pregnancies have beginnings with some chromosomal imbalance
which usually abort spontaneously during the first trimester of pregnancy.
a. True
b. False
________________________________________________________________________
________________________________________________________________________
2. Adequate nutrition, fetal monitoring, and protection from disease are the foundations of
prenatal care.
a. True
b. False
________________________________________________________________________
________________________________________________________________________
3. Recessive inheritance is associated with the production of severe disabilities and serious
health problems, such as sickle-cell anemia and cystic fibrosis.
a. True
b. False
________________________________________________________________________
________________________________________________________________________
4. Genetic screening is a measure used to identify unknown carriers of recessive traits.
a. True
b. False
________________________________________________________________________
________________________________________________________________________
5. Individuals with Prader-Willi syndrome are often of tall stature with large features.
a. True
b. False
________________________________________________________________________
________________________________________________________________________
6. Congenital syphilis is a maternal disease resulting in damage to the central nervous
system which causes severe disabilities in the developing fetus.
a. True
b. False
________________________________________________________________________
________________________________________________________________________
7. Chromosomal problems are the product of hereditary exchange.
a. True
b. False
________________________________________________________________________
________________________________________________________________________
8. In the majority of cases where amniocentesis was used its primary purpose has been to
detect the gender of the fetus.
a. True
b. False
________________________________________________________________________
________________________________________________________________________
9. Research has yet to be accumulated that may identify educational and psychological
intervention strategies that are etiology-specific.
a. True
b. False
________________________________________________________________________
________________________________________________________________________
10. Tay-Sach’s disease is inherited as an autosomal recessive trait.
a. True
b. False
________________________________________________________________________
________________________________________________________________________
Discussion
1. Discuss in detail the syndromes of mental retardation affected by metabolic factors.
2. Discuss the three methods of genetic transmission.
3. Discuss recessive and dominant inheritance.
4. Discuss the disorders associated with Down syndrome.
5. Imagine you are a parent of one child with an intellectual disability, and you and your
spouse are making plans to give birth to a second child. Utilize Graham and Scott’s
(1988) tri-level prevention strategies to determine the appropriate measures to take to
ensure the development of a healthy baby.
6. Discuss the ethical concerns of withholding medical treatment from infants when the
decision is based upon the diagnosis of intellectual disabilities.
7. Why is Fragile X syndrome only diagnosed in males?.
8. Discuss the tests commonly used for prenatal screening discussed in the text.
Answer Sheet
Multiple Choice True or False