Second, the SNP score was not statistically significantly associated with cigarettes smoked per day at age 14 or 17, but was significantly associated at age 20 and 24. If replicable, this indicates that these genetic variants are less relevant during adolescence, when a large number of individuals begin experimenting with cigarettes and/or regularly using cigarettes. Differences in effect sizes at the different ages approached statistical significance, but requires replication. This suggests the possibility of a GxD effect, and that other mechanisms, such as behavioral disinhibition, play significantly larger roles during adolescence with CPD, consistent with literature cited in the introduction. In addition to significant associations with CPD at age 20 and 24, the longitudinal study allowed us to test whether the score accounted for stability in CPD across age. The score accounted for about 1% of the covariance between age 20 and age 24 smoking, and is thus relevant to the maintenance of CPD over this four year interval.
