Gene–environment correlation
Gene–environment correlation (or genotype–environment correlation) is said to occur when exposure to environmental conditions depends on an individual's genotype.
Definition
Gene–environment correlations (or rGE) is correlation of two traits, e.g. height and weight, which would mean that when one changes, so does the other. Gene–environment correlations can arise by both causal and non-causal mechanisms.[1] Of principal interest are those causal mechanisms which indicate genetic control over environmental exposure. Genetic variants influence environmental exposure indirectly via behavior. Three causal mechanisms giving rise to gene–environment correlations have been described.[2]
- (i) Passive gene–environment correlation refers to the association between the genotype a child inherits from their parents and the environment in which the child is raised. Parents create a home environment that is influenced by their own heritable characteristics. Biological parents also pass on genetic material to their children. When the children's genotype also influences their behavioral or cognitive outcomes, the result can be a spurious relationship between environment and outcome. For example, because parents who have histories of antisocial behavior (which is moderately heritable) are at elevated risk of abusing their children, a case can be made for saying that maltreatment may be a marker for genetic risk that parents transmit to children rather than a causal risk factor for children’s conduct problems.[3]
- (ii) Evocative (or reactive) gene–environment correlation happens when an individual's (heritable) behavior evokes an environmental response. For example, the association between marital conflict and depression may reflect the tensions that arise when engaging with a depressed spouse rather than a causal effect of marital conflict on risk for depression.
- (iii) Active gene–environment correlation occurs when an individual possesses a heritable inclination to select environmental exposure. For example, individuals who are characteristically extroverted may seek out very different social environments than those who are shy and withdrawn.
Gene–environment correlation can also arise from non-causal mechanisms, including evolutionary processes and behavioral 'contamination' of the environmental measure. Evolutionary processes, such as
In this way, HbS genotype has become associated with the malarial environment.Evidence
Quantitative genetic studies
Environments are heritable because genotype influences the behaviours that evoke, select, and modify features of the environment. Thus, environments less amenable to behavioural modification tend to be less heritable.[1] For example, negative life events that are beyond the control of the individual (e.g., the death of a loved one, losing one’s home in a natural disaster) have lower heritability than negative life events that may be dependent on an individual’s behaviour (e.g., getting a divorce, getting fired from a job). Similarly, personal life events (i.e., events that occur directly to an individual) are more highly heritable than network life events (i.e., events that occur to someone within an individual’s social network, thus affecting the individual indirectly).
Molecular genetic studies
Evidence for the existence of gene–environment correlations has recently started to accrue from
A polygenic score (PGS; also called a polygenic risk score), which is a number assigned to individuals based on variation in multiple genetic loci and their associated regression weights from genome-wide association studies, can also be used to demonstrate gene–environment correlation. This effect, often referred to as "genetic nurture", is suggestive of passive gene–environment correlation when parental polygenic score independently predicts offspring outcome beyond the offspring's own PGS, and has been demonstrated for educational attainment in humans.[8][9][10]
Significance
Doctors want to know whether exposure to environmental risk causes disease. The fact that environmental exposures are heritable means that the relationship between environmental exposure and disease may be confounded by genotype. That is, the relationship may be spurious (not causal), because the same genetic factors might be influencing both exposure to environmental risk and disease. In such cases, measures aimed at reducing environmental exposure will not reduce the risk for disease. On the other hand, heritability of exposure to environmental conditions itself does not mean environmental factors are not responsible for disease and so exposure reduction would benefit individuals with genetic predisposition to risk behavior.
For example, a study of children born to twin sisters investigated whether the relationship between parental divorce and offspring alcohol and emotional problems was causal or confounded by parental genotype.[11] The study found that the offspring of twin sisters who were discordant for divorce had equally high levels of emotional problems, suggesting that genetic factors which made twin siblings divorce-prone also increased their children’s risk for depression and anxiety. This finding suggests that preventing the parents’ divorce would have had little impact on offspring risk for emotional problems (although the findings for alcohol problems in the children were consistent with a causal role for divorce).
See also
- Behavioral genetics
- Gene–environment interaction
- Genetic predisposition
- Nature versus nurture
- Niche picking
- Psychiatric genetics
- Epigenetics