Chen et al. have recently reviewed the evidence for the involvement of DNA methylation in depression, demonstrating particularly how brain-derived neurotrophic factor (BDNF) and solute carrier family 6 member 4 (SLC6A4) genes are implicated and that changes in methylation in several other genes emerging from whole-genome methylation studies have been reported 13. This evidence concerns the gene SLC6A4 and depressive disorder.