Genetics and Disease: Guyton & McCance Chapters

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Questions and Answers

What is a significant factor that makes recurrence risk estimation difficult for multifactorial diseases?

Clear distinction between polygenic and single gene diseases

Complex interactions of various genes and environmental variables (correct)

Constant recurrence risk among all family members

High penetrance of the genes involved

Which of the following correctly describes the relationship between disease severity in probands and recurrence risk?

Higher severity is associated with higher recurrence risk (correct)

Severity is irrelevant in determining recurrence risk

Higher severity leads to lower recurrence risk

Higher severity has no impact on recurrence risk

In the context of twin studies, what is the main difference between monozygotic (MZ) and dizygotic (DZ) twins regarding genetic similarity?

Neither type of twins shares any genetic similarity

Both types of twins are genetically identical

MZ twins are genetically identical, DZ twins are not (correct)

DZ twins are genetically identical, MZ are not

What does the term 'discordant' mean in the context of twin studies?

Twins do not share the trait (A) Signup and view all the answers

Which of the following statements is true regarding the occurrence of twins in different populations?

Twins occur more frequently in black populations than in white populations (B) Signup and view all the answers

In the study of adoption and disease, what conclusion can be drawn if adopted children born to diseased parents develop the disease more often than the control population?

Genetic factors likely play a role in disease causation (D) Signup and view all the answers

Which of the following statements about recurrence risk in relation to affected family members is correct?

The recurrence risk does not change with multiple affected members (C) Signup and view all the answers

What is the significance of concordance rates in the study of diseases in twins?

Concordance rates help in estimating the environmental impact on traits (B) Signup and view all the answers

What percentage of adopted children of a schizophrenic parent is expected to develop schizophrenia?

8 to 10% (C) Signup and view all the answers

What is the heritability estimate for obesity based on twin studies?

0.6 to 0.8 (D) Signup and view all the answers

Which type of diabetes has a higher concordance rate among monozygotic twins?

Type 2 diabetes (B) Signup and view all the answers

Which of the following factors significantly increases the risk of developing breast cancer?

Positive family history (C) Signup and view all the answers

What genetic characteristic is linked to susceptibility to alcoholism?

Presence of the ALDH2*2 allele (D) Signup and view all the answers

What is the proportion of the population affected by Alzheimer's disease over the age of 85?

30 to 40% (D) Signup and view all the answers

Among children with a parent suffering from schizophrenia, which risk dramatically increases if both parents are affected?

50% (B) Signup and view all the answers

Which is a key environmental risk factor for hypertension?

Smoking (D) Signup and view all the answers

Which statement about type 1 diabetes is true?

It is an autoimmune disorder (D) Signup and view all the answers

Which cancer has the strongest family correlation, particularly linked with the BRCA1 and BRCA2 genes?

Breast cancer (C) Signup and view all the answers

What is the concordance rate for schizophrenia among monozygotic twins?

47% (B) Signup and view all the answers

Which major therapeutic drugs are primarily used to treat schizophrenia?

Dopamine receptor antagonists (C) Signup and view all the answers

What does the prevalence rate of a disease reflect?

The total number of existing cases at a specific time (B) Signup and view all the answers

How do environmental factors contribute to disease incidence?

They can significantly influence disease rates across different populations. (A) Signup and view all the answers

Which of the following best describes multifactorial inheritance?

The interaction of multiple genes and environmental factors. (C) Signup and view all the answers

What role does 'threshold of liability' play in the understanding of certain diseases?

It allows for a clear determination of disease presence or absence. (B) Signup and view all the answers

Which of the following best illustrates a polygenic trait?

Height influenced by multiple genes and environment. (D) Signup and view all the answers

What does a relative risk of 24 for heavy smoking indicate?

Heavy smokers are at a significantly increased mortality risk from lung cancer. (C) Signup and view all the answers

In comparing the incidence and prevalence rates of a disease, what does a longer survival period indicate?

Prevalence can exceed incidence due to longer survival of cases. (D) Signup and view all the answers

Study Notes

Genes, Environment, Lifestyle, and Common Diseases

The presentation discusses how genes, environment, and lifestyle influence common diseases.
Module 2 focuses on describing gene influence on bodily structure and function, and how defects in genes can lead to recognizable genetic diseases. (Guyton chapter 3, McCance chapters 4, 5, and 6)
Further study from chapter 5 in McCance is recommended.

Incidence of Disease in Populations

Incidence rate: the number of new cases of a disease reported during a specific period (typically one year).
Prevalence rate: the proportion of the population affected by a disease at a specific point in time.
Prevalence rate of diseases like AIDS is often higher than incidence rates due to the survival periods of those with the disease.
The prevalence of diseases varies in different populations (e.g., cystic fibrosis is more common in Europeans than Asians, sickle cell disease is more common in African Americans).
Environmental factors play a role in the incidence of diseases like colon and stomach cancer.

Risk Factors

Relative risk: the increased rate of a disease among exposed individuals compared to non-exposed individuals.
Heavy smoking is a significant risk factor for lung cancer (24-fold increased risk of death).
Risk factors for developing diseases can be genetic or lifestyle-related (age, gender, diet, exercise, family history).
Genes involved in the metabolism of tobacco smoke components increase the risk of lung cancer for smokers.

Multifactorial Inheritance

Polygenic traits: traits in which variation is thought to be due to multiple genes.
Multifactorial trait: trait affected by more than one gene, where environmental factors also influence.
Examples of multifactorial traits include hypertension, coronary heart disease, type 2 diabetes, and some cancers.
Threshold of liability: a certain level of genetic susceptibility must be reached before a disease manifests.
This means some individuals have genes that predispose them to the disease, but the disease only manifests if certain environmental factors are present.

Recurrence Risk and Transmission Patterns

Risk estimation for multifactorial diseases is complex.
Recurrence risk is influenced by the severity of the disease in the affected individual, the sex of the affected individual, and the closeness of the relationship between the affected individual and the individual at risk.
Recurrence risk for single-gene diseases decreases by 50% with each degree of relationship, whereas it decreases more quickly in multifactorial diseases.

Twin Studies

Twins provide a natural laboratory for studying the interplay of genetic and environmental factors.
Monozygotic (MZ) twins are genetically identical.
Dizygotic (DZ) twins are fraternal, genetically different but raised in the same environment.
MZ twins are more concordant for traits determined by genes while DZ twins have similar concordance rates for traits determined by environmental factors.
Concordance rate: the percentage of twin pairs who both have a trait.
Twin studies help identify heritability estimates of specific traits.

Adoption Studies

Adopted children can help determine the influence of genetics and environment influence on disease.
The prevalence of developing a disease among adopted children whose biological parents had the disease may indicate a genetic component.
Adopted children may show a correlation with the genetic risk of their biological parents if raised in different environments.
Environmental factors can affect disease development irrespective of the biological parent's genetic predispositions.

Twins and Adoption Studies - Take Away

Common diseases are not solely determined by genetics or environment.
Genetic and non-genetic factors interact to influence the likelihood of developing a disease.

Genetics of Common Diseases

Some multifactorial disorders arise at birth, others in adolescents or adulthood.
Examples of multifactorial disorders include heart disease, cancer, diabetes, etc.
Risk factors for these disorders include obesity, cigarette smoking, hypertension, elevated cholesterol, and positive family history.

Worldwide Prevalence of Hypertension

Global prevalence of Hypertension is approximately 25-30%.
Genetic and environmental factors influence blood pressure regulation.
The renin-angiotensin system is a complex biological pathway involved in blood pressure regulation.

Cancer

The second leading cause of death in the United States.
Tobacco use is a significant risk factor for many types of cancer.
Breast Cancer is a common type, affecting a large proportion of women.
Genes like BRCA1 and BRCA2 are associated with increased risk of some types of cancer (breast and ovarian).
Several types of cancer have strong family correlations.
Colon and prostate are other prominent types of cancer.

Diabetes

Type 1 diabetes is an autoimmune disorder (0.3-0.5% risk in general population).
Type 2 diabetes is associated with insulin resistance and is frequently linked with obesity (90% of cases).
Genetic and environmental factors interact to affect risk for both type 1 and type 2 diabetes.

Obesity

Obesity is not a disease but a significant risk factor for many diseases.
Obesity is commonly linked with lifestyle behaviours and environmental components.
There is a strong familial correlation linking obesity to environmental factors in parents and offspring.

Alzheimer's Disease

Characterized by progressive dementia and memory loss.
Amyloid plaques and neurofibrillary tangles are formed in the brain.
Risk of Alzheimer's doubles in individuals with an affected first-degree relative.
Genetic predisposition and environmental factors contribute to Alzheimer's development.

Alcoholism

Diagnosed in 10% of adult males and 3-5% of adult females.
Risk increases significantly with affected parents, notably siblings.
Adoption studies highlight increased risk for offspring of alcoholic parents.
Genetic (alcohol dehydrogenase genes) and environmental factors play a role in alcoholism risk.

Psychiatric Disorders

Schizophrenia and bipolar disorder are complex psychological disorders.
Genetic factors play a significant role in risk for these disorders.
Affected first-degree relatives can greatly increase risk of schizophrenia.
Twin studies indicate a clear genetic component, and environments play a role.

Conclusions

More strongly inherited complex disorders generally have earlier onset.
Lifestyle modifications (diet, exercise, stress reduction) can significantly reduce risk.
Genetic lesion identification leads to more effective prevention and treatment.

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Description

Explore the complex interplay between genes, environment, and lifestyle factors in the development of common diseases. This quiz covers significant insights from Guyton's chapter 3 and McCance's chapters 4, 5, and 6, focusing on genetic influences and disease prevalence in various populations.