Quantitative genetic studies Gene–environment and its significance

 Journal of Pharmacology and Therapeutic Research is an open access, peer reviewed journal that focuses on the interdisciplinary research offering therapeutic solutions to various neurological, genetics, psychological, and respiratory issues affecting the human beings.

Gene–environment correlations (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. The 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.

Quantitative genetic studies

Twin and adoption studies have provided much of the evidence for gene–environment correlations by demonstrating that putative environmental measures are heritable. For example, studies of adult twins have shown that desirable and undesirable life events are moderately heritable as are specific life events and life circumstances, including divorce, the propensity to marry, marital quality and social support. Studies in which researchers have measured child-specific aspects of the environment have also shown that putative environmental factors, such as parental discipline or warmth, are moderately heritable. Television viewing, peer group orientations and social attitudes have all been shown to be moderately heritable. There is also a growing literature on the genetic factors influencing behaviors that constitute a risk to health, such as the consumption of alcohol, tobacco and illegal drugs, and risk-taking behaviors. Like parental discipline, these health related behaviors are genetically influenced, but are thought to have environmentally mediated effects on disease. To the extent that researchers have attempted to determine why genes and environments are correlated, most evidence has pointed to the intervening effects of personality and behavioral characteristics.

Environments are heritable because genotype influences the behaviors that evoke, select, and modify features of the environment. Thus, environments less amenable to behavioural modification tend to be less heritable. 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 behavior (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).

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. 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)

With Kind Regards,
Mark Orwell
Managing Editor
Journal of Pharmacology and Therapeutic Research

Email:  pharmacology@alliedresearch.org