Common Multifactorial Disorders and Traits

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Questions and Answers

What is a characteristic of multifactorial disorders in terms of inheritance patterns?

  • They are solely influenced by environmental factors.
  • They usually result from alleles at a single locus.
  • They follow Mendelian inheritance strictly.
  • They involve complex interactions of multiple genetic variants. (correct)

Which of the following describes a qualitative trait?

  • Body mass index value.
  • Presence or absence of rheumatoid arthritis. (correct)
  • Height of an individual.
  • Blood pressure measurement.

What percentage of individuals experience morbidity or premature mortality due to common diseases in their lifetimes?

  • Almost all individuals.
  • One in two.
  • Nearly two out of every three. (correct)
  • Less than one in ten.

What term is used to describe the inheritance pattern of multifactorial disorders?

<p>Complex inheritance. (C)</p> Signup and view all the answers

How do family members share genetic information compared to individuals chosen at random in the population?

<p>They share a greater proportion of genetic information. (D)</p> Signup and view all the answers

Which of the following best describes quantitative traits?

<p>They are measurable quantities that vary among individuals. (B)</p> Signup and view all the answers

Which of the following disorders is an example of a multifactorial disease?

<p>Diabetes. (B)</p> Signup and view all the answers

Why might distinguishing between individuals with a qualitative trait sometimes be difficult?

<p>Some manifestations may be subtle and require detailed examination. (C)</p> Signup and view all the answers

What defines a disease diagnosis such as short stature or hypertension?

<p>Values falling outside the normal range of a quantitative trait. (A)</p> Signup and view all the answers

Which relatives share 50% of their alleles on average?

<p>Siblings, including fraternal twins. (C)</p> Signup and view all the answers

How are alleles shared among siblings characterized?

<p>The allele sharing among siblings can vary. (C)</p> Signup and view all the answers

What is the implication of familial aggregation in diseases?

<p>Affected individuals typically have more affected relatives than expected. (C)</p> Signup and view all the answers

How can you measure the familial aggregation of a disease?

<p>By comparing the frequency of disease in relatives of the affected proband with the general population. (D)</p> Signup and view all the answers

What happens to the sharing of alleles as family members become more distantly related?

<p>They share less alleles. (D)</p> Signup and view all the answers

What is the average number of alleles shared by a pair of siblings at any one locus?

<p>1 allele. (D)</p> Signup and view all the answers

What best represents the relationship between the risk of disease and genetic relatedness?

<p>Risk increases with closer genetic relatedness. (A)</p> Signup and view all the answers

What is the primary cause of dementia in older adults?

<p>Alzheimer disease (D)</p> Signup and view all the answers

Which age group shows a significant increase in the risk of developing Alzheimer's disease?

<p>65 years and older (C)</p> Signup and view all the answers

Which factor is NOT considered a significant risk factor for Alzheimer's disease?

<p>Low physical activity (D)</p> Signup and view all the answers

What is a key challenge in understanding complex diseases such as Alzheimer's disease?

<p>Determining the role of environmental factors (C)</p> Signup and view all the answers

What is the anticipated outcome of research in population-based genetic epidemiology?

<p>Development of preventive and therapeutic measures (A)</p> Signup and view all the answers

What does a positive correlation between cholesterol measurements in patients and their relatives indicate?

<p>Higher cholesterol levels in patients are associated with higher levels in relatives. (C)</p> Signup and view all the answers

What does the heritability value (H²) of a trait signify?

<p>It indicates how much of the variability in a trait is due to genetic differences. (B)</p> Signup and view all the answers

If heritability (H²) is calculated to be 0, what does this imply about the influence of genotype on the trait?

<p>Genotype contributes nothing to the trait's variability. (B)</p> Signup and view all the answers

What is the approximate frequency of congenital heart malformations (CHDs) at birth?

<p>4 to 8 per 1000 births. (A)</p> Signup and view all the answers

How are congenital heart malformations typically classified?

<p>Some are genetic while others result from environmental impacts such as teratogens. (D)</p> Signup and view all the answers

What percentage of the global population is affected by schizophrenia?

<p>1% (A)</p> Signup and view all the answers

What is the estimated annual cost of mental illnesses in medical care and social services in the United States?

<p>$150 billion (D)</p> Signup and view all the answers

What is a characteristic of mental illnesses like schizophrenia and bipolar disorder?

<p>They are some of the most common and severe human diseases. (B)</p> Signup and view all the answers

What is a primary characteristic of schizophrenia?

<p>Abnormalities in thought and emotion (A)</p> Signup and view all the answers

What is the range of MZ concordance for schizophrenia?

<p>40% to 60% (C)</p> Signup and view all the answers

How has the nomenclature of the HLA system changed?

<p>It has shifted to include DNA sequence variants. (A)</p> Signup and view all the answers

Why is the study of familial aggregation important in complex traits?

<p>It helps understand the interaction of genotype and environment. (D)</p> Signup and view all the answers

What does a higher concordance rate in MZ twins compared to DZ twins suggest about schizophrenia?

<p>It indicates a strong genetic contribution. (B)</p> Signup and view all the answers

What is the approximate number of HLA alleles that have been defined sequenced at the DNA level?

<p>1300 (D)</p> Signup and view all the answers

What is one way modifier genes can impact single-gene disorders?

<p>They might change the phenotypic expression of the disorder. (C)</p> Signup and view all the answers

What does the term 'multifactorial traits' refer to?

<p>Traits influenced by multiple genetic and environmental factors. (C)</p> Signup and view all the answers

What characterizes disorders determined by digenic inheritance?

<p>Determined by the additive effect of genotypes at multiple loci (A)</p> Signup and view all the answers

In retinitis pigmentosa, what is true about individuals who are heterozygous for mutations at each of the two loci?

<p>They are double heterozygotes and affected. (D)</p> Signup and view all the answers

Which of the following factors increases the risk for conditions in hypercoagulability states?

<p>Environmental factors combined with genetic factors (B)</p> Signup and view all the answers

What is a consequence of the aganglionic colon in Hirschsprung disease?

<p>Total absence of intrinsic ganglion cells (C)</p> Signup and view all the answers

Which form of diabetes represents approximately 10% of all cases?

<p>Type 1 Diabetes Mellitus (A)</p> Signup and view all the answers

What is the definition of familial aggregation in the context of diabetes?

<p>One type emerges in families while the other does not (A)</p> Signup and view all the answers

Which of the following describes peripherin and Rom1 in relation to retinitis pigmentosa?

<p>They encode photoreceptor membrane proteins critical to vision (A)</p> Signup and view all the answers

What primary issue arises from the aganglionic condition in Hirschsprung disease?

<p>Severe constipation and intestinal obstruction (B)</p> Signup and view all the answers

Flashcards

Multifactorial disorders

Diseases resulting from complex interactions of multiple genes, environmental exposures, and chance events.

Complex inheritance

The inheritance pattern of multifactorial disorders, characterized by familial clustering.

Qualitative trait

A trait (like a disease) that is either present or absent; easily categorized as 'yes' or 'no'.

Quantitative trait

A measurable trait that varies continuously in a population.

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Congenital Birth Defects

A defect present at birth from genetic or environmental causes.

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Myocardial Infarction

A heart attack.

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Neuropsychiatric Disorders

Conditions affecting the brain and/or mental state, like depression or schizophrenia.

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Common Diseases

Diseases frequent and prevalent amongst the population.

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Normal Range

An arbitrary interval around the population average for a trait, used to define disease diagnoses.

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Allele Sharing (Relatives)

Close relatives share more alleles inherited from common ancestors.

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Monozygotic Twins

Identical twins with identical alleles at every locus.

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First-Degree Relatives

Close relatives like parents, children, siblings.

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Familial Aggregation

Affected individuals have more affected relatives than expected based on disease frequency.

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Relative Risk Ratio

Compares disease frequency in relatives with general population, measuring familial aggregation.

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Qualitative Trait Disease

Disease diagnoses based on whether a trait falls outside a defined normal range.

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Alzheimer's Disease (AD)

A fatal brain disorder causing memory loss and cognitive decline, affecting 1-2% of the US population, most common cause of dementia in older adults.

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Multifactorial Disease

Diseases caused by complex interactions of multiple genes, environmental factors, and chance events.

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Genetic Epidemiology

The study of how genes and environment interact to influence the occurrence and distribution of diseases in populations.

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Risk Factors for Alzheimer's Disease

Age, sex, and family history are the main factors that increase the chance of developing Alzheimer's disease.

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Challenge of Complex Inheritance

Understanding the complex interplay of genes and environmental factors for multifactorial diseases is a major challenge in medical genetics.

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Heritability (H²)

The proportion of a trait's variation within a population that can be attributed to genetic differences.

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High Heritability

A high heritability value (closer to 1) means that genetic factors account for a large proportion of the variation in a trait.

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Low Heritability

A low heritability value (closer to 0) means that genetic factors account for a small proportion of a trait's variation.

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Multifactorial Congenital Malformations

Conditions caused by a combination of genetic and environmental factors, often occurring as isolated defects.

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Congenital Heart Defects (CHDs)

A group of birth defects affecting the heart, often with a multifactorial cause.

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Schizophrenia

A severe mental illness affecting approximately 1% of the global population.

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Positive Correlation (Cholesterol)

Higher levels of a patient's cholesterol are proportionally linked to higher levels in their relatives.

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Digenic Inheritance

A type of inheritance where a disorder is caused by the combined effect of mutations at two different genes. Individuals must have mutations in both genes to develop the disorder.

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Retinitis Pigmentosa (RP)

A genetic eye disorder that can cause progressive vision loss, often due to problems with the photoreceptor cells in the retina.

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Hypercoagulability

A state of increased blood clotting tendency, leading to a greater risk of developing blood clots (thrombi) in veins or arteries.

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Gene-Environment Interaction

When the effect of a gene on a disease is modified or influenced by environmental factors. These factors can increase or decrease the risk.

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Hirschsprung Disease (HSCR)

A congenital condition where part or all of the colon lacks nerve cells (ganglion cells) needed for proper bowel function, causing severe constipation.

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Type 1 Diabetes Mellitus (T1D)

A chronic autoimmune disease where the body's immune system attacks and destroys insulin-producing cells in the pancreas, leading to high blood sugar levels.

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Complex Disease

A disease caused by a combination of multiple genetic and environmental factors, making it difficult to predict and treat.

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MZ Concordance

The percentage of identical twins who both develop schizophrenia if one twin has the disorder.

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DZ Concordance

The percentage of fraternal twins who both develop schizophrenia if one twin has the disorder.

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HLA System

A complex set of genes responsible for the immune system's ability to recognize and fight foreign invaders.

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Allele Nomenclature

The system used to name and categorize different versions of a gene (alleles).

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Modifier Genes

Genes that can influence the severity or expression of a disease caused by a mutation in another gene.

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Mendelian Disorders

Diseases caused by mutations in a single gene, following simple inheritance patterns.

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Multifactorial Traits

Traits influenced by a combination of multiple genes and environmental factors.

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Study Notes

Common Multifactorial Disorders

  • Common diseases like birth defects, heart attacks, cancer, neurological/psychiatric issues, diabetes, and Alzheimer's cause significant morbidity and mortality.
  • These diseases often cluster in families, but their inheritance doesn't follow Mendelian patterns (like single-gene disorders)
  • They result from complex interactions among multiple genes, environmental factors, and chance events, making them "multifactorial."
  • Family members share more genetic information and environmental exposures than unrelated individuals, explaining the clustering.
  • Identifying the gene variants predisposing to these common diseases is a significant challenge.

Qualitative and Quantitative Traits

  • Qualitative traits are either present or absent (e.g., lung cancer).
  • Quantitative traits are measurable physiological or biochemical values (e.g., height, blood pressure).
  • Certain quantitative traits are diagnosed when their values fall outside the "normal" range (defined by the population average ± 2 standard deviations).

Familial Aggregation

  • Family members sharing alleles increases their likelihood of sharing the same disease risks.
  • Relative risk ratio (λ) compares the disease prevalence in relatives with the general population.
  • Family history case-control studies compare affected individuals with matched controls to assess familial aggregation.

Relative Risk Ratio (λ)

  • λr = (Prevalence of the disease in relatives) / (Prevalence of the disease in the general population)
  • A value of λr greater than 1 indicates increased familial aggregation.

Twin Studies

  • Monozygotic (MZ) twins share 100% of their alleles.
  • Dizygotic (DZ) twins share approximately 50% of their alleles.
  • MZ twin concordance rates for a disease are compared to DZ rates to estimate the genetic contribution.
  • Concordance is the proportion of twin pairs where both twins have the disease.
  • The higher the concordance rate in MZ twins compared to DZ twins, the stronger the genetic influence.
  • Twin studies are used to separate genetic and environmental influences.

Heritability

  • Heritability (H²) measures the proportion of phenotypic variance attributable to genetic variation.
  • Correlation coefficients (r) measure the similarity of a trait among relatives.
  • Comparing correlations in MZ and DZ twins can provide an estimate of heritability (H²). H² = 2 x (rMZ - rDZ).
  • Heritability varies depending on the population and environment.

Multifactorial Congenital Malformations

  • Examples include cleft lip and palate, congenital heart defects, etc.
  • These defects often demonstrate familial aggregation but without clear Mendelian patterns.

Neuropsychiatric Disorders

  • Mental illnesses ("disorders") like schizophrenia and bipolar disorder are common, complex, and have high societal costs.
  • Family studies and twin studies consistently show a considerable genetic contribution to these disorders.
  • Genetic contribution is complex, involving multiple genes, often including areas of the MHC locus.

Type 1 Diabetes

  • Type 1 diabetes is an "autoimmune" disorder, often affecting young adults.
  • Strong genetic predisposition (MZ concordance significantly greater than DZ concordance).
  • Major histcompatibility complex (MHC) is a significant genetic factor and plays a critical role.

Alzheimer's Disease

  • Alzheimer's disease is a neurodegenerative disease, typically affecting older adults.
  • Genetic factors, particularly variants in the APOE gene, contribute to the disease risk.
  • The presence of the APOE e4 allele increases the risk and strongly influences age-of-onset.

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