Lecture 3

Question 1

Why Study Genetics?

Answer 1

Affects the medical decisions made by - patients, families, and their medical team • Can simplify the diagnosis, prognosis, recurrence risk, and treatment decisions

Question 2

Prevalence of congenital HL is __ in 1000 births •
By adolescence - __ in 1000
• Genetic causes contribute to the HL in __% of cases

Answer 2

• 2 in 1000
• 3.5 in 1000
• 50%

Question 3

• -% of childhood HL is genetic • In most cases, no family hx hearing loss

Answer 3

50-60

Question 4

_______- that which is inherited

________ - that which is expressed

Answer 4

• Genotype

- Phenotype

Question 5

______ when something happens to a gene to change it into a new variant - genetic condition is a result of a variant in a gene that alters the body’s instructions from the way they normally work

Answer 5

mutation

Question 6

Chromosome Abnormalities

• How? - Usually from an error in cell division. There are two kinds of cell division - name them

Answer 6

mitosis and meiosis.

• Mitosis results in two cells that are duplicates of the original cell. One cell with 46 chromosomes divides and becomes two cells with 46 chromosomes each. This kind of cell division occurs throughout the body, except in the reproductive organs. This is the way most of the cells that make up our body are made and replaced.
• Meiosis results in cells with half the number of chromosomes, 23, instead of the normal 46. This is the type of cell division that occurs in the reproductive organs, resulting in the eggs and sperm.

Question 7

________ _______a genetic condition that arises when only one copy of a gene is altered

Answer 7

dominant condition

Question 8

_______ ______- both copies of a gene are the same variant

Answer 8

recessive condition

Question 9

_______- passed on from one or both parents to the child

Answer 9

inherited

Question 10

Genetic condition is the result of a mutation/change in a gene that alters the body’s instruction. What does this include?

Answer 10

• Autosomal Dominant Inheritance
• Autosomal Recessive Inheritance
• X-Linked Inheritance
• Mitochondrial inheritance

Question 11

Autosomal dominant with 1 affected parent and 1 unaffected parent. What are the odds of passing down the gene with 4 children?

Answer 11

50% chance of child inheriting it. 50% unaffected, 50% affected

Question 12

What are the hallmarks of autosomal dominant inheritance?

Answer 12

There is a 50% chance of inheritance per offspring
Failure of trait to be displayed is caused by variable expressivity
Those who display the disorder are typically heterozygous for the trait

Question 13

Huntington’s disease is an autosomal ______ disease.

Answer 13

dominant

Question 14

Autosomal dominant with 1 affected parent and 1 unaffected parent. What are the odds of passing down the gene with 4 children?

And, those who display the disorder/disease are _______.

Answer 14

• 25% chance of offspring getting disease
• 25% chance of offspring having two normal genes
• 50% chance of offspring being carriers
• homozygous

Question 15

Phenylketonuria is an example of an autosomal ________ disease.

Answer 15

-recessive

Question 16

What are the hallmarks of X-Linked recessive inheritance?

Answer 16

• Caused by gene alteration on the x chromosome
• Males have only one X chromosome and will therefore develop the condition
• Females need both copies of the deviant gene to display the phenotype
• Typically females are carriers and males exhibit the trait
• With a female (mother) carrier:
• 50% chance of each daughter inheriting the gene and being a carrier
• 50% chance of each son inheriting the gene and inheriting the condition
• When a male (father) has the condition:
• sons will not be affected
• daughters will be carriers without the condition

Question 17

Lesch-Nyhan Syndromeis an example of an ______ ______ disease

Answer 17

X-linked recessive

Question 18

X-Linked Dominant Inheritance - describe what it is and how it affects offspring

Answer 18

• Caused by gene alteration on the x chromosome
• Males and females with the altered gene will display the
phenotype
• Affectedmother:
50% of offspring are unaffected 50% of offspring have the disorder
• Affectedfather:
100% of daughters have the disorder No sons will have the disorder

Question 19

Alport syndrome is an example of an ______ ________ disease

Answer 19

X-linked dominant

Question 20

_______ genes are passed on by the mother only
Referred to as “maternal inheritance”
If all ______ are affected, likely the embryo won’t survive
otherwise likely inherited two types of _______ from mom (some with working copy of the gene, and some with mutation)

Answer 20

• Mitochondrial
• mitochondria
• mitochondria

Question 21

With mitochondrial inheritance, can it occur in every generation of family (even if mother is asymptomatic)?
Can it affect both males and females Threshold effect?

Answer 21

yes and yes

Question 22

Mitochondrial inheritance:

1. If the father has the disease. will the children?
2. if the mother has the disease (all mitochondria mutant) will the children have the disease?
3. If the mother has the disease (some mitochondria normal, others mutant) will the children have the disease?

Answer 22

1. no
2. yes - assuming complete penetrance
3. children may or may not have the disease (and severity may vary)

Question 23

Process of providing individuals and families with information on the nature, inheritance and implications genetic conditions.

Answer 23

genetic counseling

Question 24

What are the reasons for seeking counseling?

Answer 24

- after child is first 
 diagnosed
   -understand the    
    condition, prognosis 
    and help make 
    decisions
- as part of 
  family planning
     -recurrence risks, 
     preimplantation 
     genetic diagnosis, 
    prenatal diagnostic 
     testing

Question 25

when is genetic counseling is recommended?

Answer 25

• any family with a child with HL
• Complex family history, pregnancy, birth, and medical history
• Physical exam of child and family members -Laboratory work-up
• Following exam, the family is given the diagnosis and prognosis

Question 26

Definition: The examination of an individual’s chromosomes, genes, proteins and/or other analytes for alterations associated with genetic disorders or conditions

Answer 26

genetic testing

Question 27

Why genetic testing?

Answer 27

Might provide a definitive diagnosis of a genetic disorder, identify one’s risk for developing a particular genetic disorder, or determine whether an individual is at risk for having a child with a particular genetic disorder
Can sometimes help predict the severity of a disorder or determine the best course of treatment for a patient
If negative, may rule out a particular genetic disorder in a patient or allow for recalculation of the risk that a particular genetic disorder might occur in an individual or their children

Question 28

Limitations of Genetic Testing?

Answer 28

Most medical genetic tests are specific for a particular disorder and cannot identify disorders not directly tested.
Although medical genetic tests can often help with the diagnosis of a genetic disorder, they may not always be able to predict the age of onset or severity of a disorder, or determine the best course of treatment for a patient.
If negative, medical genetic tests may offer limited information leaving the doctor, patient, and family knowing little more than they did before the test.

Question 29

Risks of Genetic Testing

Answer 29

• The physical risks typically small, especially if the test being ordered requires only a blood or urine sample, or a cheek swab.
• If tissue samples or biopsies are required, the physical risks may be higher and will depend on the type of sample that is required and how it must be obtained.
• In the case of prenatal testing, some tests such as chorionic villus sampling (CVS), amniocentesis, or fetal blood sampling (cordocentesis) have a small risk of miscarriage, while other tests such as fetal ultrasonography do not
• Possible emotional and social consequences: feelings of anger, guilt, anxiety, or depression.
• Concerns about financial consequences of genetic testing and the potential for discrimination in or loss of employment or insurance.