Possible association between DBH 19 bp insertion/deletion polymorphism and clinical symptoms in schizophrenia with tardive dyskinesia
Overactivity of dopaminergic neurotransmission is a putative mechanism of tardive dyskinesia (TD). Previous studies have found dysfunction in plasma dopamine beta-hydoxylase (DBH) in schizophrenia with TD. Moreover, DBH, whose activity and levels are strongly controlled by the DBH gene, is a key enzyme in the conversion of dopamine (DA) to norepinephrine (NE) associated with excited behavior. This study examined whether the DBH5′-insertion/deletion (Ins/Del) polymorphism was associated with excited behavior in schizophrenia with TD. The presence of the DBH5′-Ins/Del polymorphism was determined in 741 schizophrenia with TD (n = 345) and without TD (n = 396). The Abnormal Involuntary Movement Scale and Positive and Negative Syndrome Scale were used to assess the severity of TD and psychopathology of schizophrenia. There was no significant difference in the allelic and genotypic frequencies of the DBH5′-Ins/Del polymorphism between schizophrenia with and without TD (both p > 0.05). However, the excited symptoms score was significantly different to the DBH5′-Ins/Del genotypic groups in schizophrenia with TD (p < 0.05) but not in the two groups of non-TD and total patients (both p > 0.05). The excited symptoms score was higher in TD patients with the Del/Del genotype than those with Ins alleles (p = 0.015). Our findings suggest that the DBH5′-Ins/Del polymorphism may not contribute directly to the development of TD in schizophrenia, but it may be involved in the excited behavior of TD patients.