BDNF and psychotic disorder: Despite ongoing uncertainty regarding the reliability of peripheral tissues, such as blood and saliva, as biomarkers for neuropsychiatric disorders, a study using blood samples from individuals experiencing their first episode of psychosis identified a connection between elevated levels of TET1, neuregulin 1 (NRG1), brain-derived neurotrophic factor (BDNF), and DNMT1, and the onset and progression of schizophrenia.105