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The Nature of the Shared Environment
Kenneth S Kendler1,2, Henrik Ohlsson3, Paul Lichtenstein4
1Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Box 980126, Richmond, VA, 23298-0126, USA. Kenneth.Kendler@vcuhealth.org.
Behavior Genetics
|December 12, 2018
Summary
Shared environment effects (c^2) on familial resemblance vary by estimation method. Twin studies yield higher shared environment estimates than step-sibling or half-sibling designs, highlighting the need to refine the definition of "shared environment".
Area of Science:
- Behavioral Genetics
- Quantitative Genetics
- Population Genetics
Background:
- Shared environment (c^2) is a standard component in twin modeling but its magnitude is infrequently compared across different estimation methods.
- Understanding the impact of shared environmental factors on familial resemblance is crucial for disentangling genetic and environmental influences on complex traits.
Purpose of the Study:
- To compare shared environment (c^2) estimates for 20 diverse phenotypes across three distinct familial designs: twins, step-siblings, and half-siblings.
- To investigate how different family structures influence estimates of environmental effects on resemblance.
- To clarify the range of environmental processes encompassed by the term 'shared environment'.
Main Methods:
- Utilized data from the Swedish general population.
- Estimated shared environment (c^2) for 20 phenotypes using monozygotic and dizygotic twins.
- Estimated c^2 using step-siblings and reared together/apart half-siblings.
Main Results:
- Mean c^2 estimates were higher in twins (0.18) compared to step-siblings (0.12) and half-siblings (0.09).
- Moderate correlations (ICC = +0.28) were observed between c^2 estimates across the three methods.
- Step-siblings from adoption-like families showed significantly lower resemblance than those from blended families.
Conclusions:
- The magnitude of shared environment effects on familial resemblance is dependent on the methodology employed.
- Current definitions of 'shared environment' may encompass diverse processes that yield varying estimates across different study designs.
- Further research is needed to refine the conceptualization and measurement of shared environmental influences in behavioral genetics.
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