Hippocampal volume and serotonin transporter polymorphism in major depressive disorder

The main aim of the present study was to replicate a previous finding in major depressive disorder (MDD) of association between reduced hippocampal volume and the long variant of the di- and triallelic serotonin transporter polymorphism in SLC6A4 on chromosome 17q11.2. Secondarily, we also hypothesised that 5-HTTLPR may be a risk factor for MDD.

Quantitative magnetic resonance imaging (MRI) of the hippocampus was studied in 23 inpatients suffering from MDD and in 33 healthy controls. Normalised volumetric MRI data of hippocampus were assessed with adjustment for total brain volume and tensor-based morphometry was used to elucidate structural brain differences. A triallelic genetic marker resulting from two SLC6A4 promoter region polymorphisms, 5-HTTLPR and rs25531, was analysed for association with MDD and quantitative traits.

Healthy controls had a smaller relative hippocampal volume (relative to brain size) but a larger total brain volume compared with patients with MDD. For patients compared with healthy controls, atrophy was found in the right temporal lobe and pons medulla. Allele and genotype frequencies were strikingly different from the previous study that we aimed to replicate, and no significant associations with the serotonin transporter polymorphism were found.

The present quantitative and morphometric MRI study was not able to replicate the previous finding of association between reduced hippocampal volume in depressed patients and the serotonin transporter polymorphism.