Neurobiological disorder: An illness of the nervous system caused by genetic, metabolic, or other biological factors. Many illnesses categorized as psychiatric disorders are neurobiological, including autism, bipolar disorders, obsessive-compulsive disorders, schizophrenia, and Tourette syndrome Neurobiological brain disorder (NBD), (or neurobiological disorder (NBD)) refers to disease or other biological processes affecting the brain. Any condition that affects the functioning of the brain and may be caused by genetics, metabolic, endocrinological, auto-immune, infectious agents, agents, extreme environmental factors triggering biological changes, or other biological factors are included.