Association between 5-HTTLPR polymorphism and Parkinson's disease: a meta analysis

To investigate the genetic association of 5-HTTLPR polymorphism and Parkinson's disease (PD) or depression in PD by using meta analysis. Published association studies on genotype or allele frequencies of the 5-HTTLPR in patients with or without PD or in PD patients with or without depression in all ethnic groups were included. A biallelic meta-analysis, including biallelic frequency model, biallelic dominant model (BDM) and biallelic recessive model, was performed using the Cochrane Review Manager (RevMan, version 5.2) to calculate the pooled odds ratio and its corresponding 95 % CI with a random-effect model. Six studies met the criteria for the meta-analysis of association of 5-HTTLPR and three studies were included for the association of 5-HTTLPR and depression in PD. The meta-analysis results did not show significant association between 5-HTTLPR and PD or depression in PD, except for a moderate negative association between 5-HTTLPR and PD in Asian subgroup (2 studies) using the BDM approach. Our meta-analysis result does not support a direct primary effect of 5-HTTLPR on PD or depression in PD. Further association studies with larger sample sizes preferably taking into consideration factors such as additional allelic variants in the 5-HTTLPR, ethnic variation of the 5-HTTLPR distribution and gene-gene interaction are necessary to reach a more definite conclusion.