The effect of smoking amount is not evident among African Americans, where the increased lung cancer risk associated with two of the three SNPs was independent of smoking dose. Results were most significant in African Americans for rs1051730, which is in a LD block encompassing CHRNA3/CHRNA5. Although variant alleles were less frequent in African Americans, risk in this group was similar if not greater than that in whites. Reasons underlying the racial difference in the genotype/smoking amount associations are unknown. It is possible that cigarettes per day do not adequately measure nicotine dependence in African Americans. It is also possible that a marker linked to the SNPs studied is the causal variant, and the frequency of that marker and its association with number of cigarettes smoked varies by race.
