These are adjustment disorder with depressed mood, major depressive disorder, dysthymia, and bipolar disorder. The symptoms of it mimic those of dysthymia or even major depressive disorder. Milder but still prolonged depression can be diagnosed as dysthymia. There is a high incidence of comorbid illness in those with dysthymia. RIMAs are used clinically in the treatment of depression and dysthymia. Positive antibody titers to "T. gondii" appear to be uncorrelated with major depression or dysthymia. A smaller hippocampus has been linked to depression and dysthymia. A "double depression" is the occurrence of episodes of major depression in addition to dysthymia. Dysthymia often co-occurs with other mental disorders. Psychotherapy is often effective in treating dysthymia. People with dysthymia have a higher-than-average chance of developing major depression. There is some evidence of a genetic basis for all types of depression, including dysthymia. Suicidal behavior is also a particular problem with persons with dysthymia. There is evidence that there may be neurological indicators of early onset dysthymia. In more severe cases of dysthymia, people may even withdraw from daily activities.