, 2010). Kessler et al. (2009) suggest that only nicotine dependence and not less severe smoking phenotypes remains significantly associated with suicide plans after adjusting for potential confounders. In addition to Y-27632 price diagnostic criteria for smoking, heaviness of smoking is associated with suicide with evidence of a dose�Cresponse relationship between cigarettes smoked per day and risk for suicide attempt and completed suicide (Beratis, Lekka, & Gabriel, 1997; Hemenway, Solnick, & Colditz, 1993; Hemmingsson & Kriebel, 2003; Iwasaki, Akechi, Uchitomi, & Tsugane, 2005). Multiple explanations for this association have been posited including lower serotonergic functioning and low monoamine oxidase activity (Malone et al., 2003; Whitfield et al., 2000).

In a review of the literature, Hughes (2008) presents both causal (smoking as a physiological/psychological toxin or that smokers self-medicate for depression) and noncausal (via a third correlated measure) hypotheses linking current smoking and smoking cessation to suicide. A potential noncausal influence is common familial vulnerability. Though we are not aware of twin studies that have estimated the common genetic contribution to smoking and suicide, we know that both behaviors are heritable. The estimates of the genetic contribution to regular smoking range between 58% and 74% (Heath & Martin, 1993; Madden, Pedersen, Kaprio, Koskenvou, & Martin, 2006; Pergadia, Heath, Agrawal, et al., 2006; Pergadia, Heath, Martin, et al., 2006; True et al., 1997, 1999).

Genetic factors have been found to account for 33%�C70% Entinostat of the variance in risk for developing nicotine dependence (Heath & Madden, 1995; Heath & Martin, 1993; Kendler et al., 1999; Lessov et al., 2004; Maes et al., 2004; True et al., 1999). The genetic contributions to suicidal ideation and suicide attempt range from 36% to 43% and from 30% to 55%, respectively (Glowinski et al., 2001; Fu et al., 2002; Statham et al., 1998). Furthermore, the risk of ideation and attempt is significantly higher in family members of patients who have committed suicide as compared with those who have not (Brent & Mann, 2005). In addition, given evidence that suicide and smoking ��run in families,�� it is possible that familial risk factors may partially account for the observation that smoking is a risk factor for suicide (Qin, Agerbo, & Mortensen, 2003). However, evidence that parental smoking is associated with offspring suicidal behavior is inconclusive (Hockenberry, Timmons, & Vander Weg, 2010). To our knowledge, no studies have simultaneously controlled for familial risk from parental suicidal behavior and parental smoking while estimating the relationship between suicide and smoking in the offspring generation.