There has been extensive research concerning the role of the serotonin transporter gene (SLC64A) in depression. The STin2 VNTR polymorphism in the second intron has been found to influence the transcriptional activity of the gene, however, its relationship to major depressive disorder (MDD) has so far been less widely investigated.

71 MDD patients and 99 healthy controls participated in a case-control study. In case of the two populations STin2 allele frequencies were compared. The subjects also completed several tests to establish neurocognitive endophenotypes related to MDD.

A significantly higher frequency of the STin2 10/10 homozygous genotype in the MDD patients’ group was found compared to controls (X2=6,01, df=2, P<0.05). The results of neurocognitive tests indicated cognitive dysfunctions in case of MDD patients compared to controls. The clinical subgroup with at least one copy of the 10-repeat allele showed a decreased interference threshold in attention and cognitive interference as compared to patients without the 10-repeat allele. Average performance of the clinical subgroup without the 12-repat allele proved to be significantly weaker in the verbal learning memory and recall tasks compared to patients having at least one copy of the 12-repeat allele.

After further confirmation our results suggest that the presence of STin2.10 and absence of STin2.12 allele may be considered a possible genetic endophenotype for cognitive dysfunctions detected in MDD.