Recent studies suggest that it is vital researchers overcome barriers to designing effective risk prevention and treatment programs for various diseases (Milunsky, 2001). One way to achieve this is via more genetic research, providing researchers more data and information regarding the manifestation of illness. Four such studies exploring the link between genes and disease states in humans are described below. .

             Overview.

             Crabbe (2002) provides a Meta analysis and comprehensive overview of the literature that focuses on genetic effects on disease and studies exploring the effects of genetics on disease in human and in animal models. The author reviews traditional studies and studies exploiting "new molecularly based technologies" in an attempt to identify the role genetics plays in addiction related diseases and in an attempt to identify future directions for genetic testing and use of animal and human models to help understand disease and brain "dysregulations" that may contribute to addictions in humans (Crabbe, 435). .

             The author first works to define addiction, assuming that genetic studies can help clarify addiction by providing evidence of a physiological basis for addictive behaviors. The author concentrates his investigation on drug abuse in particular, and characterizes addiction as a "craving" and physiological altering of the metabolism and expulsion of certain drugs. The author highlights multiple studies providing a "neurobiological foundation" for drug addiction, suggesting that historical evidence suggests that "dysregulation in brain circuits" serve as the underlying contributor to most addictions, and that various hypothesis also support gene involvement including one's natural tendency to efficiently metabolize and excrete certain drugs (Crabbe, 2002). Genetic variation, according to the author, may give rise "to individual behavioral differences due to DNA sequence differences" that ultimately predispose someone to addictive tendencies and help regulate the body's ability to metabolize certain drugs efficiently or inefficiently (Crabbe, 2002).