Second, gene-environmental interactions are central to understanding the role of genetics in disease. Even in the cases of single gene disorders, the severity and timing of genetic expression are affected by environmental triggers, and known genetic risks can be exacerbated or become protective because of specific environmental exposures.138, 145 Intriguing patterns of interaction between genetic factors and psychosocial risk factors have been identified that could shed light on the patterning of disease by race.146 A recent study of 590 participants from the 2004 Florida Hurricane Study found that two aspects of the macro-social environment (county level crime rate and unemployment rate) both interacted with a specific genetic trait (5-HTTLPR) in predicting PTSD risk.147 Similarly, analysis of data for adolescents in the Add Health Study found that genetic traits interacted with family processes (e.g., daily family meals), school processes (e.g., repeating a grade) and friendship network variables (e.g., friend delinquency) to predict delinquency and violence among male adolescents.148
