The etiology of primary dystonia remains unclear. Recent genetic studies suggest that the Val66Met polymorphism of the BDNF gene is a genetic modifier in cranial-cervical dystonia in Caucasians. However, the finding is not consistent.

Inconclusive results have been reported in studies investigating the association between the brain-derived neurotrophic factor (BDNF) rs6265 polymorphism and migraine. In the present study, we conducted a systematic review and meta-analysis on the published data in order to quantitatively estimate the relationship between rs6265 and migraine susceptibility. A comprehensive search was performed through PubMed, Web of Knowledge, and Cochrane databases up to October 2016. The pooled odds ratio (OR) with the corresponding 95% confidence interval (CI) was calculated to estimate the strength of the association with rs6265 under an additive, dominant, or recessive model of inheritance. A total of five studies including 1,442 cases and 1,880 controls were identified for the meta-analysis. The pooled data showed an increased risk of migraine for the allelic (OR: 1.17, 95% CI: 1.03-1.34, p=0.014) or the dominant model of rs6265 (OR: 1.22, 95% CI: 1.05-1.41, p=0.011). Statistical significance of rs6265 was lost when one single study was excluded from the analysis (dominant OR: 1.17, 95% CI: 1.00-1.38, p=0.054; allelic OR: 1.14, 95% CI: 0.99-1.31, p=0.067), suggesting lack of robustness of pooled estimates. When stratified by migraine type, a similar trend of association was detected with both MA and MO, but a statistically significant association of rs6265 was reached only with the MA subtype in the dominant model (OR: 1.22, 95% CI: 1.00-1.47, p=0.047). The present meta-analysis supports that BDNF rs6265 may act as a genetic susceptibility factor for migraine. Nevertheless, large-scale studies are required to confirm our findings and to assess potential modifiers of the relationship between rs6265 and migraine.

Parkinson's disease (PD) is a complex neurodegenerative disorder. Although the p.G2385R allele of leucine-rich repeat kinase 2 (LRRK2) has been recently reported as a common genetic variant that increases the risk for typical PD exclusively among Asian population, its genetic modifiers is yet to be studied. Brain-derived neurotrophic factor (BDNF) has been shown to play an important role in the survival of dopaminergic neurons and its genetic polymorphism was associated with an increased risk for PD at an older age onset. The current case-control study was performed to investigate the interaction between LRRK2 p.G2385R and BDNF p.V66M in a Chinese PD cohort. A total of 464 PD patients and 549 controls were involved in this study.LRRK2 p.G2385R variant (odds ratio [OR]=3.2; 95% confidence interval [CI]=1.96-5.15, p<0.0001), not BDNF p.V66M alone significantly increased the risk of PD. However, the simultaneous presence of bothLRRK2 and BDNF variants significantly enhanced the risk for PD (OR=4.033; 95% CI=2.188-7.435, p<0.0001), particularly in patients with an onset age of older than 60 (OR=6.439; 95% CI=3.096-13.389, p<0.0001). Our results further support that LRRK2 variants are an independent genetic risk factor for typical PD, but BDNF variants can greatly increase LRRK2-induced risk for patients with an onset age of older than 60 indicating an additive effect between the 2 genes, which might aid in studying the mechanism underlying LRRK2 parkinsonism and developing potential therapeutic strategies.