The genetics of smoking initiation and quantity smoked in Dutch adolescentand young adult twins

Not much is known about the genetic and environmental determinants of vario us aspects of substance use in adolescents. This study examined whether the inheritance of initiation of tobacco use in adolescents is independent of the inheritance of the number of cigarettes smoked. Alternative multifactor ial threshold models were applied to data on tobacco use in 1676 Dutch adol escent twin pairs. The three models that were considered are (i) the single liability dimension model, (ii) the independent liability dimension model, and (iii) the combined model (CM), The results showed that there is not on e underlying continuum of liability to smoking. The CM was the best-fitting model. This model postulates that there are separate initiation and quanti ty dimensions but allows for the possibility that there are some individual s who are so low on the liability to level of consumption that they are not using tobacco. There were no differences between males and females in the magnitude of the genetic and environmental influences on individual differe nces in smoking initiation and quantity smoked. Smoking initiation was infl uenced by genetic factors (39%) and shared environmental influences (54%), Once smoking is initiated genetic factors determine to a large extent (86%) the quantity that is smoked.