Interestingly, in the study by Ferrer et al. (2019), patients with major depressive disorder (MDD) showed an association between BDNF promoter IV methylation at CpG sites 5, 9, and 10 and poorer cognition in several cognitive domains (verbal and visual learning and memory, working memory, processing speed, and executive functioning). This evidence concerns the gene BDNF and major depressive disorder.