Gene–environment interaction
Gene–environment interaction (GxE) is a critical concept in understanding how both genetic predispositions and environmental factors influence health and well-being. Researchers investigate how different genotypes respond to the same environmental conditions and how the same genotypes fare in varied environments. This interaction is significant in predicting the risk of diseases such as cancer, diabetes, and asthma, as well as in psychological conditions. Environmental risk factors include a wide range of influences, from exposure to chemicals and injuries to lifestyle choices like diet and exercise.
Studies on GxE often involve family histories, as well as animal models that allow for controlled experimentation. Notably, prenatal factors can have lasting effects on health, potentially influencing individuals across multiple generations. In psychology, GxE research highlights how genetic vulnerabilities, such as those affecting serotonin transport, can be exacerbated by environmental stressors, leading to conditions like depression. Overall, understanding GxE interactions is essential for developing effective prevention strategies and treatments for various health issues.
Gene–environment interaction
Medically speaking, both genes and environment affect well-being. Researchers work to understand both influences and how they interact. They study people with different genotypes (the genetic makeup of an individual or group) in the same environment and people with the same genotypes in different environments to find similarities and differences. This gene–environment interaction is represented as "GxE." These factors affect how studies are constructed and interpreted, and help researchers predict risk of disease in individuals and the population. Study of GxE in cancer, obesity, asthma, diabetes, and other conditions and in psychology is ongoing.
Overview
The study of genetics is complicated. Even in close relatives, genes vary greatly. Many diseases tend to show up in families but remain difficult to predict. Environmental factors influence genetic predisposition, and researchers work to understand this impact. Genes also influence a predisposition to disease. As gene research advances—for example, the human genome project—experts increasingly are able to pinpoint genetic influences. Medical researchers are interested in which genes predispose individuals to disease and to what degree. Since the waning years of the twentieth century, epidemiology, the science of studying and treating disease, has increasingly focused on this genetic component and environmental effects.
Researchers study three variables: environmental risk factors, high-risk genotypes, and disease. Environmental risk factors include exposures, behavior patterns, and life events—for example, chemicals, exercise, foods, injuries, mold, nicotine, radiation, and viruses. High exposure to ultraviolet (UV) radiation, for example, increases everyone's risk of skin cancer. Those with an autosomal recessive disorder called xeroderma pigmentosum, however, produce less of an enzyme that helps repair DNA damaged by UV radiation. These individuals are at greater risk of developing skin cancer, as long as they are exposed to UV radiation. If they were protected from all exposure, however, their risk would be the same as others' risk.
Studying Gene–Environment Interaction
Many studies of gene–environment interaction involve taking histories of families in which a genetic predisposition has been found. Even within a family, many environmental factors will be inconsistent. Studies may take many years, and the familial link may be broad—extending from parents and offspring to extended branches of the family. In addition, not all members of a family may be willing to participate, which leaves gaps in the data.
Animal studies are able to introduce and control specific environmental factors; successive generations of mice and rats, for example, may be examined in a comparatively short period of time. Scientists are able to genetically modify the animals to more closely resemble human physiology.
The National Institute of Environmental Health Sciences reports that prenatal environmental exposures may be more influential than previously believed. Studies indicate a connection between prenatal malnourishment and diseases later in life, including diabetes and heart disease. Scientists believe both the types and timing of influences are important factors in disease development. Fetuses are exposed to chemicals and other elements of the mother's environment. They lack immune systems and are growing cells and forming tissues that may be affected by these factors. Fetal exposure to environmental factors may persist for as many as four generations, affecting the health of an individual's great-grandchildren. Such information may help scientists find new ways to prevent disease.
Psychology
Researchers are studying the gene–environment connection in psychology and psychopathology. For example, some individuals are genetically predisposed to a condition that slows serotonin transfer in the brain. Such individuals are more likely to experience depression brought about by stress, which is an environmental risk factor.
A 1958 study demonstrated the gene–environment interaction. Researchers bred rats for a maze-running experiment. One group, called maze bright, performed well in the maze. A second group, called maze dull, made many mistakes. Once the rats' skills were measured, their environments were changed. Some were kept in highly stimulating cages full of items they could move and explore. Others were in plain cages without toys. Maze bright rats in the enriched environment performed the same as before in the maze. Maze dull rats in the stimulating environment performed better, matching the maze bright rats' performance. Maze dull rats kept in barren cages performed the same in the maze, but maze bright rats kept in the same dull environment performed poorly—they made as many mistakes as the maze dull rats.
Human studies are much more complicated because of ethical concerns. To compensate, researchers have studied families, adoptees, and twins. A 1990 Danish study compared high-risk children of schizophrenic mothers who were raised in institutional settings to other children in institutional settings. Researchers found a higher risk of schizophrenia in the children of schizophrenic mothers. The same study found these children to be at greater risk for developing an enlarged heart, while children of two schizophrenic parents were at even greater risk for developing an enlarged heart.
Adoption studies compare adoptees with their biological (genetic) relatives and their adoptive (environment) families. In many cases, adoptees developed disorders found in their genetic backgrounds—such as alcoholism and personality disorders—more often when they were raised in stressful family environments, indicating the strong influence of environment.
Some twin studies compare monozygotic, or identical, twins, while others look at dizygotic, or fraternal, twins. Identical twins share their genetic variations, but fraternal twins share only about half their genetic structure. Several famous studies have examined identical twins raised apart to determine the influence of genes versus environment.
Bibliography
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