Association of Dopamine Beta-Hydroxylase Polymorphisms with Alzheimer’s Disease, Parkinson’s Disease and Schizophrenia: Evidence Based on Currently Available Loci

BACKGROUND/AIMS: The neuropathies Alzheimer's disease (AD), Parkinson's disease (PD), and schizophrenia (SCZ) have different pathological mechanisms but share some common neurodegenerative features, such as gradual loss of neuronal structure and function. Dopamine beta-hydroxylase (DBH), a gene located in the chromosomal region 9q34, plays a crucial role in the process of converting dopamine into norepinephrine (NE). Several case-control studies have reported this pathway in the pathogenesis of AD, PD and SCZ. However, the results are controversial. METHODS: We conducted a meta-analysis to estimate the associations between polymorphisms in this gene and AD, PD and SCZ. Seven databases (PubMed, Embase, Web of Science, China National Knowledge Infrastructure (CNKI), Wan Fang, SZ Gene and AD Gene) were searched to identify eligible studies. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to evaluate the associations of DBH variants with AD, PD and SCZ susceptibility. RESULTS: A total of 41 studies involving 10506 cases and 15083 controls were included in our meta-analysis. The analysis results indicated that a lack of association (P > 0.05) was observed between most of the currently available DBH polymorphisms and the neurological diseases AD, PD and SCZ; however, the DBH rs1611131 (allelic model: OR = 0.889, 95% CI: 0.815 - 0.969; dominant model: OR = 0.868, 95% CI: 0.778 - 0.968), rs2283123 (allelic model: OR = 0.285, 95% CI: 0.095 - 0.862; dominant model: OR = 0.290, 95% CI: 0.094 -0.897) and rs2007153 (allelic model: OR = 2.196, 95% CI: 1.506 - 3.200; dominant model: OR = 2.985, 95% CI: 1.465 - 6.084; recessive model: OR = 2.729, 95% CI: 1.548 - 4.812) variants were shown to be significantly associated with the risk of AD (the former variant) and SCZ (the latter two variants). CONCLUSION: On the one hand, most DBH polymorphisms from the currently available loci showed no linkage to AD, PD or SCZ, indicating the lower possibility of these loci serving as genetic markers of the risks of diseases with neurodegenerative characteristics. On the other hand, the DBH rs2283123 and rs2007153 polymorphisms could have opposite effects on SCZ development in Caucasians and be more specific in Croatians, while the DBH rs1611131 minor variant might have a protective effect on AD risk in Caucasians; however, these results require further study.