E-final 3d
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- Heredity & Envmt
- Both can play a role in diseases occurrence, but how do we differentiate them? Historically we have looked at “family history†of a particular disease But how do we differentiate actual inheritable risk factors versus those shared due to shared behaviors or environmental exposures?
- Heredity & Exposure
- How do heredity factors play a role in disease occurrence in populations? Increased/decreased susceptibility to an agent or exposure some hereditary factors may be modified by intervention of various sorts degree of importance can vary in subgroups of the population
- Detecting heredity factors
- Assess associations and heterogeneity in cases Identification of genetic markers Examining age of onset patterns in cases Conducting family and twin studies
- Assess associations
- If a disease is associated with another that is known to have a strong genetic component, it is suggestive that genetics may play an important role identifying groups of cases that may reflect different causal pathways - hereditary and non-hereditary
- ID of genetic markers
- Based on phenotype expression - blood type, eye or hair color Direct or indirect analysis of the DNA itself laboratory testing for specific genes
- Examining age of onset patterns in cases
- Diseases with a strong hereditary etiology often have much earlier onset than non-hereditary forms or diseases Still requires describing a biologic mechanism for the difference in presentation
- Conducting family studies
- Must distinguish between blood relatives versus legally defined relatives, since families can share both genetic material and environmental exposure look at first degree relatives versus spouses Describe both phenotype and genotype pedigrees to identify possible inheritance patterns Can also assess linkages between genes that may be inherited together
- What is a twin?
- All twins are not the same Monozygote twins “Identical twinsâ€, resulting from the early division of a single fertilized egg Dizygote twins “fraternal twinsâ€, resulting from 2 eggs fertilized by 2 different sperm, effectively siblings born at the same time
- Conducting twin studies
- Must differentiate between monozygote and dizygote twins Concordance in monozygote twins is less informative than discordance when discordance exists it is highly suggestive of an environmental origin for the disease When mono- and dizygote twins are compared: a genetic disease should demonstrate less concordance in the dizygote twins than in the monozygote twins Sample size is always a potential problem for twin studies
- Adoption studies
- Examining both diseased and non-diseased adoptees for both their environmental and biologic risks can also help to delineate the respective roles for heredity and environment - “nature versus nurtureâ€
- Migrant studies
- Group-level “adoption†Can investigate if/how shifts from “normal†for country of origin to “normal†for destination country occur Many factors to consider - selection criteria, age at move, immersion in new culture
- Migrant study ex
- One of the classics in this area deals with the emigration and acculturation of ethnic Japanese in the US Disease experience in emigrant, 1st and 2nd generation US-born individuals demonstrated relative roles of heredity and environment on health status and disease occurrence
- Rarely all or nothing
- Possible genetic and environmental factors contributing to disease etiology all need to be examined Respective contributions of either can vary across sub-groups, and may be amenable to modification or remediation Improvements in technology will expand our understanding of the contribution of all of these factors