Alcohol dependence (AD) is one of the most common and costly public health problems in the United States and throughout the world, affecting 4-5% of the United States population in a 12-month period (Kessler, 2005; Li et al., 2007), and 12.5% across the lifetime (Hasin et al., 2007). Family, twin, and adoption studies have provided convergent evidence for the role of genetic factors in AD (Goodwin et al., 1974; Heath et al., 1997). Approximately 40% to 60% of the total variance in risk for AD is due to heritable influences (Prescott et al., 2006; Schuckit et al., 2001).
