or an allele specific TaqMan single nucleotide polymorphism genotyping assay (Applied Biosystems)
and real-time polymerase chain reaction. Individuals were genotyped for CYP2A6*2,
CYP2A6*4, CYP2A6*9, and CYP2A6*12 alleles, which were selected based on their
known role in decreasing nicotine metabolism [3]. Subjects were categorized as normal,
intermediate, or slow CYP2A6 genotype metabolizers based on the metabolic impact of
CYP2A6 genotype [3]. Normal metabolizers (NM) had no variant alleles (100% CYP2A6
activity), while intermediate metabolizers (IM) had 1 copy of a decreased-function variant
allele (CYP2A6*9 or CYP2A6*12; ~80% CYP2A6 activity), and slow metabolizers (SM)
had 2 copies of a decreased-function allele or 1 or 2 copies of a loss-of-function variant
allele (CYP2A6*2 or CYP2A6*4; ≤50% CYP2A6 enzymatic activity).