PMP22 and depressive disorder: Microarray analysis of post-mortem tissues from patients with depression has shown significant downregulation of myelination or oligodendrocyte lineage-related transcriptional genes, particularly those crucial for myelin structure, such as 2′,3′-cyclic-nucleotide 3′-phosphodiesterase (CNP), myelin-associated glycoprotein (MAG), myelin and lymphocyte protein (MAL) [86], myelin oligodendrocyte MOG, myelin-associated oligodendrocytic basic protein (MOBP), peripheral myelin protein-22 (PMP22), and PLP, as depression severity increases [71, 87].