section_path: Pathophysiology
section_name: Pathophysiology
paragraph_text: Pathophysiology
  
  There is no known unifying underlying pathophysiology for suicide; it is believed to result from an interplay of behavioral, socio-economic and psychological factors.
  
  Low levels of brain-derived neurotrophic factor (BDNF) are both directly associated with suicide and indirectly associated through its role in major depression, post-traumatic stress disorder, schizophrenia and obsessive–compulsive disorder. Post-mortem studies have found reduced levels of BDNF in the hippocampus and prefrontal cortex, in those with and without psychiatric conditions. Serotonin, a brain neurotransmitter, is believed to be low in those who die by suicide. This is partly based on evidence of increased levels of 5-HT2A receptors found after death. Other evidence includes reduced levels of a breakdown product of serotonin, 5-hydroxyindoleacetic acid, in the cerebral spinal fluid. However, direct evidence is hard to obtain. Epigenetics, the study of changes in genetic expression in response to environmental factors which do not alter the underlying DNA, is also believed to play a role in determining suicide risk.