Genetic analyses of smoking initiation, persistence, quantity, and age-at-onset of regular cigarette use in Brazilian families: the Baependi Heart Study

The data set consisted of 1,694 individuals enrolled in the Baependi Heart Study. The heritability and the heterogeneity in genetic and environmental variance components by gender were estimated from variance components approaches, using the SOLAR (Sequential Oligogenic Linkage Analysis Routines) computer package. The mixed-effects Cox model was used for the genetic analysis of the age-at onset of regular cigarette use.The heritability estimates were high (> 50%) for smoking initiation and were intermediate, ranging from 23.4 to 31.9%, for smoking persistence and quantity. Significant evidence for heterogeneity in variance components by gender was observed for smoking initiation and age-at-onset of regular cigarette use. Genetic factors play an important role in the interindividual variation of these phenotypes in females, while in males there is a predominant environmental component, which could be explained by greater social influences in the initiation of tobacco use.Significant heritabilities were observed in smoking phenotypes for both males and females from the Brazilian population. These data add to the literature and are concordant with the notion of significant biological determination in smoking behavior. Samples from the Baependi Heart Study may be valuable for the mapping of genetic loci that modulate this complex biological trait.Annually, tobacco smoking is responsible for 5.4 million deaths worldwide [1], with more than 200,000 occurring in Brazil alone. Although smoking prevalence is decreasing as a result of public policies for the prevention and control of the tobacco epidemic, approximately 15.1% of Brazilian adults continue to smoke, with prevalence higher among males (17.9%) than females (12.7%) [2].The natural history of addiction to nicotine can be characterized in stages. An individual first tries a puff or two, and eventually smokes a whole cigarette. Those who experience particular reinforcing biological or psycho-social influences will con