IGFBP2 and major depressive disorder: The numbers of IGFBP2‐positive cells decreased in the hippocampus of a mouse model of amyotrophic lateral sclerosis, and serum IGFBP2 levels were lowered in patients with bipolar disease and depression.2 IGFBP2 plays a key role in neurite outgrowth and the early induction of spines, as well as SPAR cytoskeletal construction and NR2B expression.