According to the results of a study reported in 2017 (Ullrich et al. 2018), upregulated expression and functioning of the brain derived neurotrophic factor (BDNF)/receptor tyrosine kinase B (TrkB)/ERK-MAPK system (Guiton et al. 1994; Huang and Reichardt 2001, 2003)⁠ especially in the circuits of the thalamo-amygdala region, might be responsible for the observation of obsessive-compulsive disorder-like behaviors (OCD). The gene discussed is BDNF; the disease is obsessive-compulsive disorder.