BDNF and major depressive disorder: Examples are links: between polymorphism in solute carrier family 6 member 4 (SLC6A4) gene with defect in facial emotion recognition in schizophrenia (7), between polymorphism in 2’3’-cyclonucleotide 3’-phosphodiesterase (CNP) gene with psychopathological symptoms including catatonia, depression, anxiety, and autism manifestations (8) and polymorphism in a brain-derived neurotrophic factor (BDNF) gene with symptoms of insertion and withdrawal of thoughts, verbal hallucinations, and delusions (9).