Chapter 5: Genes, Environment-Lifestyle, and Common Diseases

relative risk

A common measure of the effect of a specific risk factor is this risk ratio: increase rate of disease among individuals exposed -------------------------- incidence rate of the disease among those not exposed

Which gene is linked with breast cancer?

BRCA1

Which of the following are congenital diseases? (Select all that apply.) Hydrocephaly Clubfoot Cleft lip Obesity

Hydrocephaly Clubfoot Cleft lip NOT obesity

Which statement regarding coronary heart disease is true?

It is the leading killer of Americans.

Several criteria are used to define multifactorial inheritance:

(a) the recurrence risk becomes higher if more than one family member is affected; (b) if the expression of the disease in a proband is more severe, the recurrence risk is higher; (c) the recurrence risk is higher if the proband is of the less commonly affected sex; (d) the recurrence risk for the disease usually decreases rapidly in more remotely related relatives; and (e) if the prevalence of the disease in a population is f, the risk for offspring and siblings of probands is approximately the square root of f .

empirical risks

(i.e., risks based on direct observation of data)

For most multifactorial diseases, empirical risks

(risks based on direct observation of data) have been derived.

phocomelia

(severely shortened limbs) in babies. thalidomide, a sedative used during pregnancy in the early 1960s caused this

quantitative traits

(those, such as blood pressure, that are measured on a continuous numeric scale) are multifactorial.

BRCA1 is located on chromosome 17. BRCA2 is located on chromosome ???

13

Alzheimer disease affects approximately

5% to 10% of the population, age 65 years and older

Which statement is true regarding Alzheimer disease?

Alzheimer disease is characterized by progressive dementia and memory loss.

Dizygotic or fraternal rates are the same among populations. T or F

FALSE: Dizygotic or fraternal rates vary among populations.

discordant trait

If both members of a twin pair do not share the trait

Concordant trait

If both members of a twin pair share a trait (e.g., a cleft lip), it is said to be a

1) What is the definition of incidence rate?

Number of new cases of a disease reported during a specific period, divided by the number of individuals in the population

Which statement regarding hypertension is true?

One of the most important factors affecting blood pressure is sodium intake.

Which statement is true regarding the risks of developing a disease?

Recurrence risk is higher if more than one family member is affected.

Monozygotic twins have the same rate across populations. T or F

TRUE

Which statement is true regarding type II diabetes?

These individuals experience insulin resistance.

liability distribution

Those individuals who are on the "low" end of the distribution have little chance of developing the disease in question (i.e., they have few of the alleles or environmental factors that would cause the disease). Individuals who are closer to the "high" end of the distribution have more of the disease-causing genes and environmental factors and are more likely to develop the disease.

polygenic

Traits in which variation is thought to be caused by the combined effects of multiple genes ("many genes")

Which statement describes a monozygotic twin?

Twins who share all traits Monozygotic twins divide from one embryo and actually share traits.

multifactorial trait

When environmental factors are also believed to cause variation in the trait, which is usually the case

Relative risk is

a common measure of the effect of a specific risk factor. It is expressed as a ratio of the incidence rate of the disease among individuals exposed to a risk factor divided by the incidence of the disease among individuals not exposed to a risk factor.

Dizygotic twins are the result of

a double ovulation followed by the fertilization of each egg by a different sperm.

factors that influence the risk of acquiring a common disease:

age, gender, diet, exercise, and family history of the disease.

ADH is aldehyde dehydrogenase, which is responsible for

alcohol metabolism.

For diseases that have a threshold of liability,

an individual usually does not have the disease below the threshold of liability.

Few traits are influenced only by genes or only by environment. Most

are influenced by both.

Congenital diseases

are present at birth.

Dizygotic (DZ, fraternal) twins

are the result of a double ovulation followed by the fertilization of each egg by a different sperm. Thus dizygotic twins are genetically no more similar than siblings.

Congenital diseases are those present

at birth. Most of these diseases are multifactorial in etiology.

Many factors can influence the risk of acquiring a common disease, such as

cancer, diabetes, or hypertension.

It is incorrect to assume that the presence of a genetic component means that the course of a disease

cannot be altered—most diseases have both genetic and environmental aspects.

In contrast to most single-gene diseases, recurrence risks for multifactorial diseases can

change significantly from one population to another because gene frequencies, as well as environmental factors, can differ among populations.

Many of the common adult diseases, such as hypertension, coronary heart disease, stroke, diabetes mellitus (types 1 and 2), and some cancers, are caused by

complex genetic and environmental factors and are thus multifactorial diseases.

If both members of a twin pair share a trait, they are said to be

concordant.

Multifactorial diseases in adults include

coronary heart disease, hypertension, breast cancer, colon cancer, diabetes mellitus, obesity, AD, alcoholism, schizophrenia, and bipolar affective disorder.

If both members of a twin pair do not share the same trait, they are

discordant.

Twins from double ovulation are

dizygotic and may not share traits

Those diseases, however, that do not follow a bell-shaped distribution appear to be

either present or absent in individuals. They do not follow the inheritance patterns of single-gene disease. Instead, such diseases may follow an underlying liability distribution. It is thought that a threshold of liability must be crossed before the disease is expressed.

The term multifactorial is used when

environmental factors also are believed to cause variation in the trait.

When a disease has a relatively larger genetic component, as in breast cancer, examination of WHAT should be emphasized?

family history in addition to lifestyle modification.

Family members share genes and a common environment; therefore, resemblance in traits, such as high blood pressure, reflects both

genetic and environmental factors (nature and nurture, respectively).

Recurrence risk is higher if

more than one family member is affected and usually decreases rapidly in more remotely related relatives.

Many quantitative traits (e.g., blood pressure) are

multifactorial.

threshold of liability

must be crossed before the disease is expressed. Below the threshold, an individual appears normal; above it, he or she is affected by the disease.

incidence rate

number of new cases of a disease reported during a specific period (typically 1 year) divided by the number of individuals in the population.

Empiric risks are based on

observation (not assumptions)

Monozygotic (MZ, identical) twins

originate when, for unknown reasons, the developing embryo divides to form two separate but identical embryos. Because they are genetically identical, MZ twins are an example of natural clones.

Traits in which variation is thought to be caused by the combined effects of multiple genes are

polygenic.

The proportion of the population affected by a disease at a specific point in time is the

prevalence rate

Examples of diseases that correspond to the liability model include

pyloric stenosis, neural tube defects, CL/P, and some forms of congenital heart disease.

The effect of a specific risk factor is the

relative risk.

Because traits are caused by the additive effects of many genetic and environmental factors, they

tend to follow a normal or bell-shaped distribution in populations.

Monozygotic twins originate when

the developing embryo divides to form two separate but identical embryos.

Studies of adopted children also are used to estimate

the genetic contribution to a multifactorial trait.

The incidence rate is

the number of new cases of a disease reported during a specific period (typically 1 year) divided by the number of individuals in the population.

The prevalence rate is

the proportion of the population affected by a disease at a specific point in time. This rate, and the incidence rate, can be used to compare population variations in disease frequency.

A genetic predisposition may interact with an environmental-lifestyle factor to increase

the risk of disease; this is called a gene-environment interaction.

Two research strategies often are used to estimate the relative influence of genes and environment-lifestyle:

twin studies and adoption studies.

Polygenic genes cause

variation

prevalence rate,

which is the proportion of the population affected by a disease at a specific point in time.

example of gene-environment interaction

α1-antitrypsin deficiency, a genetic condition that causes pulmonary emphysema and is greatly exacerbated by cigarette smoking