Genetic correlations between smoking initiation and smoking behaviors in a twin sample.

Early exposure to cigarettes is connected to increasing rate of regular use later in life. We examine genetic correlation between the age of first cigarette and later smoking related behaviors. The sample consisted of twin ages 25 to 75. Biometrical analysis was used to evaluate the heritabilities and a second analyses based on Cholesky decomposition determined the shared variance. The genetic variance ranged from 48% to 69%. Models comparing age of first cigarette to and smoking persistence, cessation, and number of cigarettes during year smoked most individually indicated a very small proportion of shared genetic variance (ranging from 0.004 to 0.056). These findings support separate genetic and unshared environmental processes for the age of first cigarette as compared to three other smoking related phenotypes. Research in substance abuse risk and prevention literature suggests that delaying initial exposure is a critical step reducing in the risk of later regular use. The interventional implications of the findings support the importance of a tailored approach to preventing smoking behavior and reducing harm in smokers.