The 3′ UTR gene conversion defining the CYP2A6*1B allele is believed to stabilize the mRNA transcript, leading to higher CYP2A6 protein levels [35] and faster in vivo nicotine metabolism [27]. When we repeated the comparison based on the limited genotyping described by Mwenifumbo et al. [27](i.e. comparing *1B homozygotes to all other diplotypes excluding *1B,*2,*4,*7,*9,*10,*12 and *14 carriers) we also found a significant difference in metabolism efficiency (91% vs. 86%, p=0.0002)). However, this difference is due overwhelmingly to the *1A(51A) allele which constituted 34% (35/102) of alleles in our sample termed “*1A” by Mwenifumbo et al. according to their restricted genotyping and subject selection [27]. Based on our comparison of the *1B and *1D haplotypes (Table 4), which are identical except for the 3′ UTR conversion (Table 1 and [24]), we conclude that any effect of the 3′ UTR conversion on in vivo nicotine metabolism is negligible.
