8/27/14 - Genetics of Complex Diseases Flashcards
Familial aggregation of a disease provides evidence of what?
A genetic component to a disease.
What major environmental factor is associated with neural tube defects?
Folic acid deficiency
What is discorance?
The presence of a certain trait in only one member of a twin pair.
What is a monozygotic twin?
Identical twin; one zygote splits into two shortly after fertilization
How would you interpret a relative risk ration
When
How would you interpret a relative risk ratio >1?
When >1, there is likely a genetic component to the disease
What is a modifier gene?
One gene that can modify the expression of another.
How might a modifier gene influence incomplete penetrance?
It may completely silence a disease-causing gene, in which case the individual would not have clinical symptoms of the disease.
Diseases where greater concordance is seen in monozygotic twins than dizygotic twins suggest what?
There is a genetic component to the disease.
Why might there exist a complex and Mendelian form of Hirschprung disease?
Locus heterogeneity; either the loss/mutation of a single gene or a number of genes can lead to the same phenotype.
What is a quantitative or continuous trait?
A trait with a variable phenotype; it is not simply present or absent (e.g. height).
What is the most common mode of inheritance of retinitis pigmentosa?
Dominant
How is the heritability of complex traits determined and why?
Empirical risk tables, since they can’t be predicted based on the principles of Mendelian inheritance.
How might young women be at an increased risk for idiopathic cerebral vein thrombosis?
Oral concentrations increases blood plasma levels of factor X and prothrombin. Combined with mutations in the genes encoding Factor V and prothrombin, there is a 20-fold increase in susceptibility
What were the findings in concordance studies between monozygotic twins reared together and apart?
They have similar concordance, suggesting that genetic factors are more important than environmental factors to a specific disease.
What is the definition of relative risk?
A quantitative measure of the degree of familial aggregation of a disease.
What is a qualitative or dichotomous trait?
A trait that is either present or absent, and is almost always attributable to different alleles of single genes.
What is concordance?
The presence of a certain trait in both members of a twin pair.
What is a dizygotic twin?
Fraternal twin; two eggs are fertilized by two sperm
What is the relationship between variance and the contributions of genes and environment to quantitative traits?
Values near 0 imply that variability for a specific measurement is almost exclusively due to environmental factors. Values near 1 imply that variability is almost exclusively due to genetic factors.
What gene is most commonly mutated in Hirschprung disease?
RET
What is familial aggregation of a disease?
The occurence of a disease in more members of a family than can be explained by chance.
Qualitative traits almost always follow the principles of which type of inheritance?
Mendelian
How might a modifier gene influence variable expressivity?
It may reduce or increase expression of a disease-causing gene, leading to less or more severe symptoms, respectively.
