SP4 and bipolar disorder: In particular, we have shown reduced immunoreactivity of SP4 in the postmortem cerebellum and prefrontal cortex of subjects with bipolar disorder [11]; a negative association of SP4 immunoreactivity with negative symptom severity in the cerebellum of patients with schizophrenia [12]; and altered SP4 levels in the postmortem hippocampus of subjects with schizophrenia and in a mouse model of acute psychosis [13].