Common variants have been associated with altered cholinesterase activity in samples drawn from the community [36]. The SNP rs1803274 is a common variant in BCHE, and the A allele leads to a point mutation at nucleotide 1615 that changes codon 539 from GCA (ala) to ACA (thr) [38]. In carriers of the A allele, serum BChE levels are reduced by 30%. Decreased BChE activity increase the amount of cocaine that reaches the reinforcing brain areas, thereby augmenting its propensity to lead to dependence. Most cocaine users in Brazil have equal access to crack and powder cocaine, and the AA genotype can, in part, explain the fact that some users prefer to use crack cocaine exclusively. It is likely that the enzymatic changes interact with other known predisposing factors for crack dependence and account for part of the genetic vulnerability to this route of administration.
