The DSM-IV-TR includes diagnostic criterion sets to assist clinicians in making the accurate diagnosis, as well as a section devoted to differential diagnosis when persons fulfill diagnostic criteria for more than one illness. The four major categories of disorders include mental illnesses, developmental disabilities, substance use disorders, and behavioral syndromes. Mental illnesses are conditions characterized by abnormal thoughts, emotions, or behaviors that cause significant distress or impairment in social functioning. Examples include anxiety disorders, attention-deficit/hyperactivity disorder (ADHD), bipolar disorder, depression, and schizophrenia. Developmental disabilities are chronic conditions that affect brain development. They can be physical, such as cerebral palsy, or cognitive, such as intellectual disability or autism. Substance use disorders are patterns of behavior marked by excessive use of alcohol or other substances that result in negative effects for the user. Behavioral syndromes are long-term problems that affect a person's mood, behavior, and ability to function daily life tasks. They often begin in childhood and continue into adulthood. Examples include obsessive-compulsive disorder (OCD) and tic disorders. Each mental illness and developmental disability has its own set of symptoms and treatment guidelines. However many people suffer from more than one mental illness at a time. For example, someone may have symptoms of depression and also have ADHD. When this occurs, it is called comorbidity.