from the 3′ end of the CYP2A6 gene to the 3′ end of the CYP2A7 gene (Figure S6), which is a region that encompasses all five CNP markers. Since the CYP2A6 gene encodes a nicotine-metabolizing enzyme [12], [13], it is reasonable to speculate that this common deletion may directly cause a loss of function of the CYP2A6 gene that would result in slow nicotine metabolism. Indeed, the estimated effect size of one copy of the CYP2A6 gene corresponding to approximately three cigarettes per day (Table S2 and Figure S7).
