and the nature of particular symptoms experienced when a smoker stops smoking (Pergadia et al., 2006).
Numerous studies have attempted to identify genes underlying nicotine addiction (Lessov-Schlaggar et al., 2008), but studies of the genetics of nicotine dependence and smoking behavior are problematic because such complex behaviors are determined by multiple genes and by environmental factors. Recent genomewide association studies have pointed to several genes that are promising signals for genetic determinants of nicotine dependence. Bierut et al. (2007) studied a phenotype that is thought to reflect susceptibility to nicotine dependence and showed a significant association with genes that code for components of nicotinic receptors found in the brain (Saccone et al., 2007). Other genomewide association studies have identified a number of genes that affect cell adhesion and extracellular matrix molecules. The genes are common among various addictions; this is consistent with the idea that neural plasticity and learning are key determinants of individual differences in vulnerability to nicotine and other drug addictions (Kauer and Malenka, 2007; Uhl et al., 2007).
Genetic studies have identified genes that encode parts of the receptors for the neurotransmitter gamma-aminobutyric acid (Grucza and Bierut, 2006). Those genes may be involved in the development of alcohol and nicotine dependence. Siblings of alcohol-dependent people had a 1.7 times higher risk of becoming habitual smokers than did siblings of nonalcoholics; if the alcohol-dependent people were habitual smokers, the siblings’ risk was a increased further by a factor of 1.8 (Bierut et al., 1998, 2000).
People who have mental illness or substance-abuse disorders have higher rates of smoking. Results of the National Comorbidity Survey (NCS) show that 41.0% of people who had a mental illness in the preceding month were current smokers, compared with 22% of those who did not, and 60% of those with a lifetime history of mental illness were smokers (Lasser et al., 2000). Moreover, people with mental illness consume over 44% of all cigarettes sold in the United States (Lasser et al., 2000). The 2001–2002 NESARC found that 12.8% of the US population was nicotine-dependent and consumed 57.5% of all cigarettes. Nicotine-dependent people who had a mental illness amounted to 7.1% of the US population but consumed 34.2% of all cigarettes (Grant et al., 2004).
Specifically, smoking prevalence is higher in people who have the following diagnosed disorders than in the general population: