Recent years several studies have attempted to examine the associations between polymorphisms of COMT, DRD4, DRD2, DAT1, MAOA, 5-HTTLPR, and executive functions. These studies have never been...Show moreRecent years several studies have attempted to examine the associations between polymorphisms of COMT, DRD4, DRD2, DAT1, MAOA, 5-HTTLPR, and executive functions. These studies have never been combined in a meta-analysis. In this thesis a meta-analysis is carried out for each gene separately. This leads to a central research question: Do people with risk variants of dopamine genes or the risk variant of 5-HTTLPR perform worse on executive function tasks than people without these risk variants? Several databases were searched for relevant studies relating the polymorphisms of COMT, DRD4, DRD2, DAT1, MAOA, and 5-HTTLPR to executive functions. This resulted in 23 studies in the meta-analysis of COMT, 10 studies for DRD4, 6 for DRD2, 9 for DAT1, 4 for MAOA, and 9 for 5-HTTLPR. The meta-analyses only included studies with a non-clinical sample. Significant associations between polymorphisms of COMT and DRD4 and performance on executive function tasks were found. Both set of studies were however not homogene, so these results must be interpreted carefully. Also, a moderator analysis for COMT was carried out to examine whether a difference could be found between the effect size of cognitive flexibility and the effect size of other executive functions. The results showed that the polymorphism of COMT was significantly more associated with cognitive flexibility than with other executive functions. Despite several limitations of this study regarding the overlap between executive functions and the disadvantages of meta-analytic techniques, this study contributes to more understanding of the association between genes and executive functions.Show less
