Kreek et al.’s review of the research on genes and addiction offered a three-domain model that included genetics, diverse environmental factors, and drug-induced effects. (Figure 1) (Kreek, Nielsen, & LaForge, 2004) In 1960, Kaij et al. conducted the first study of alcoholism in twins and in 1966, Partanen et al. conducted a similar twin study which further explored the associations between intelligence, personality, and alcohol consumption. These were the earliest studies proposing that specific addictions were heritable, or influenced by genes. (Kaij & Rosenthal, 1961; Partanen, Bruun, & Markkanen, 1966) An adoption study by Cloninger et al. concluded that genes influence alcohol abuse since adopted away probands had a greater resemblance…show more content… A large number of twin studies have reported significant heritability for tobacco addiction in different populations, regardless of sex or age. (Carmelli, Swan, Robinette, & Fabsitz, 1992; A. Heath, Kirk, Meyer, & Martin, 1999; A. C. Heath, Madden, Slutske, & Martin, 1995; Kendler, Thornton, & Pedersen, 2000; Koopmans, Slutske, Heath, Neale, & Boomsma, 1999) Mcgue et al., in a twin study, found that the heritability of tobacco use and nicotine dependence was 40% to 60%. (McGue, Elkins, & Iacono, 2000) ) A family study by Cheng et al. identified a major segregating factor for “ever-smoking”, or lifetime cigarette smoking. (Cheng, Swan, & Carmelli, 2000) With data from families in the Collaborative Study on the Genetics of Alcoholism (COGA), some linkage studies have reported that several specific chromosome sections are associated with smoking behaviors. Bergen et al. reported some linkage between smoking behaviors and chromosomes 6, 9 and 19. Additionally, linkage existed between several candidate gene regions and smoking pack-year history. (A. W. Bergen, Korczak, Weissbecker, & Goldstein, 1999) Duggirala et al. also found linkage between smoking pack-year history and a genetic region on chromosome 5q, suggesting that a variant or variants near this marker (D5S1354) on chromosome 5q might be the primary determinant of genetic variation in smoking. (Duggirala, Almasy, & Blangero, 1999) This site is also…show more content… Two twin studies estimate the heritability of alcohol addiction at 48% to 58% for males and 51% to 59% for females. (Kendler, Neale, Heath, Kessler, & Eaves, 1994; Prescott & Kendler, 1999) Due to the nearly ubiquitous exposure to the substance, alcohol offers a unique way of understanding the probability of/susceptibility to addiction since all “controls”, or non-dependent individuals, are likely to have been exposed. In 1989, the COGA began to identify genes implicated in alcoholism. (Edenberg, 2002) Investigators in the COGA study refined the definition of alcoholism beyond that in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IIIR).Using a family-based linkage study design, they found that drug and/or alcohol dependence are associated with a handful of identified “regions of interest” on human chromosomes 1, 2, 3, 4, 7, and 11. (Foroud et al., 2000; Long et al., 1998; T. Reich et al., 1998; Stallings et al., 2003) In the same way that certain genes make people more susceptible to addiction, other genes seem to make people less susceptible. Clinical observations of Asians with different phenotypes in metabolizing alcohol were the earliest studies on the genetics of vulnerability to addiction. Many Asians of the same ethnic descent exhibit a distinct facial flushing and experience severe hangover effects after consuming alcohol. As a result, many Asians in this population have an aversion to alcohol. Consequently,
