To our knowledge, only a few adolescent twin studies of depression and smoking have been carried out, all of which were conducted in U.S. and European settings. A study of Finnish adolescent twin pairs who were discordant for depressive disorders found that history of depressive disorder occurring prior to age 14 predicted use of smokeless tobacco by age 17.5 increased risk www.selleckchem.com/products/AP24534.html for daily smoking, but did not predict smoking initiation (Sihvola et al., 2008); this study did not utilize genetic modeling approaches. In a genetic modeling study of U.S. adolescent twins, Silberg, Rutter, D��Onofrio, and Eaves (2003) found that early experimental smoking and depression were genetically correlated in girls but environmentally correlated among boys. Finally, in U.S.

adolescent twin pairs, McCaffery, Papandonatos, Stanton, Lloyd-Richardson, and Niaura (2008) found that nonshared environmental factors explained the relation between level of depressive symptoms and smoking involvement and that there was a common genetic source of depression�Csmoking covariation in girls. Given the substantial public health burden of smoking in Asian countries, such as China (Qian et al., 2010), it is important to understand influences on smoking initiation in Chinese adolescents. A sizeable number of Chinese begin smoking in adolescence, with evidence that for boys, the hazard of smoking initiation is very low (<2%) before 7 years of age, increases rapidly after age 10 years, and peaks at 14�C15 years, whereas the hazard for girls is low (<1%) until 12 years of age before it increases by age 15 years, but the overall prevalence of smoking is higher in boys than in girls (Chen et al.

, 2001). The cultural characteristics of Asia are different from western societies, which may modulate the expression of genetic vulnerabilities on depressive symptoms, smoking initiation, and their association (Unger et al., 2011). For example, although most Asian countries have laws restricting Entinostat youth access to tobacco, enforcement of these policies is inconsistent, and it is common for adults to offer cigarettes to adolescents on special occasions or as a rite of passage into adulthood (Okamoto et al., 2010). Adolescents in China often report high levels of academic stress because admission to prestigious high schools is very competitive, and they tend to report smoking to cope with stress while studying for stressful exams (Booker et al., 2007; Okamoto et al., 2010). Also, Asian populations also have different allele frequencies for genetic variants implicated in depression and smoking (e.g., Kang, Palmatier, & Kidd, 1999).