Altered expression and coregulation of dopamine signalling genes in schizophrenia and bipolar disorder.

INTRODUCTION: signalling through dopamine receptors is of critical importance in the brain and is implicated in schizophrenia and bipolar disorder, but its underlying molecular mechanisms remain poorly understood.
MATERIALS AND METHODS: using a yeast two-hybrid approach, we previously identified 11 novel dopamine receptor-interacting proteins. Here we compare gene expression levels for 17 genes [including all 11 dopamine receptor interacting proteins, all 5 dopamine receptors (DRD1-DRD5) and DARPP-32] by real-time polymerase chain reaction, using prefrontal cortex post mortem brain samples from 33 schizophrenic, 32 bipolar disorder and 34 control subjects.
RESULTS: the expression of C14ORF28, GNB2L1, MLLT3, DRD2 and DARPP-32 genes was altered in schizophrenia and/or bipolar disorder samples relative to controls (P < 0.05). Hierarchical clustering analysis revealed the expression of these five genes (C14ORF28, GNB2L1, MLLT3, DARPP-32, DRD2) is closely correlated in patients. However, in controls, DRD2 expression in relation to the other genes appears to be very different, suggesting abnormal DRD2 activity is an important trigger in the pathophysiology of schizophrenia and bipolar disorder.
CONCLUSIONS: our data suggest: (i) C14ORF28, GNB2L1, MLLT3, DRD2 and DARPP-32 are important in the pathogenesis of schizophrenia and bipolar disorder; (ii) these two disorders share common disease-related mechanisms linked to dopamine signalling; (iii) the expression of these genes is closely correlated; and (iv) DRD2 provides the initial trigger in the pathogenesis of these disorders.