Stratification analysis was used to find the genetic interaction between these two VNTRs in nicotine dependence as they may synergistically regulate the SLC6A4 expression.
Previous studies have implicated genes encoding the 5-HT3AB receptors (HTR3A and HTR3B) and the serotonin transporter (SLC6A4), both independently and interactively, in alcohol (AD), cocaine (CD), and nicotine dependence (ND).
A serotonin transporter gene, SLC6A4, is thought to be related to nicotine dependence and depression, one of the comorbidities of chronic obstructive pulmonary disease (COPD).
Our data suggest that a decreased expression of the gene encoding the 5-HTT transporter, due to "S" promoter polymorphism, may be associated with smoking behavior among adolescents and increased risk to develop nicotine dependence, possibly in relationship to personality traits, temperamental characteristics, and school under-achievements.