This result was somewhat surprising given the strong correlations between drinking and smoking behaviors (Miller and Gold, 1998). Twin studies suggest that common genetic influences are partially responsible for the observed correlation (Swan et al., 1997; True et al., 1999), though disorder-specific genetic influences have been identified as well (Kendler et al., 2007; Volk et al., 2007). Nonetheless, previous family-based samples selected for alcohol dependence have identified genetic loci that confer risk to alcohol and tobacco use phenotypes. For example, loci on chromosomes 2 (Bierut et al., 2004), 4 (Ehlers and Wilhelmsen, 2006), 7 (Loukola et al., 2008; Sullivan et al., 2008), and 18 (Sullivan et al., 2008) have been shown to contribute jointly to alcohol and nicotine dependence The lack of such findings in the present study suggest that unique genetic influences contributed to nicotine and alcohol dependence in the UCSF Family Alcoholism Study.
