Reduced hippocampus volume and memory performance in bipolar disorder patients carrying the BDNF val66met met allele.

•BDNF val66met polymorphism was related to hippocampus and verbal memory in bipolar (BD) and major depressive disorder (MDD).•BDNF met allele carrier BD patients had smaller hippocampus and worse verbal memory compared to MDD patients and controls.•BDNF val66met polymorphism was a putative biological signature for the neuroanatomical and cognitive abnormalities in BD.