3.2. Overall and subgroup analysis
A meta-analysis of 6 SNPs was performed, as can be seen in Table 2. Apart from rs894278, remaining 5 SNPs were statistically significant (rs356186, rs2736990, rs3822086, rs7684318, and rs3857059). Of these five SNPs, three added the risk of PD (rs2736990, rs3822086, and rs3857059), and two reduced the susceptibility to PD (rs356186 and rs7684318) in the total populations. Regarding the six SNCA SNPs, we investigated the contributions of allele, dominant, recessive, heterozygote and homozygote concerning each variant using five models. In the whole population, rs2736990 polymorphism augmented the PD susceptibility by five models (OR=1.28-1.64, P=0.000), while rs7684318 polymorphism decreased the risk of PD under all genetic models (OR=0.47-0.70, P=0.000). Rs3857059 aggrandized the risk of PD under allelic (OR=1.28, 95% CI: 1.01–1.63, P=0.044) and recessive model (OR=1.49, 95% CI: 1.11–2.00, P=0.008).
A cross-ethnic analysis was further conducted. In the East Asian group, the carrier rs3822086 was significantly related with PD under the allelic (OR=1.25, 95% CI :1.11–1.41, P=0.000), homozygous (OR=1.50, 95% CI: 1.18–1.89, P=0.001), heterozygous (OR=1.30, 95% CI: 1.06–1.59, P=0.012), dominant (OR=1.36, 95% CI: 1.12–1.65, P=0.002) and recessive model (OR=1.42, 95% CI: 1.03–1.97, P=0.032). Rs2736990 was significantly related with the high-risk PD under allelic(OR=1.22, 95% CI: 1.11–1.35, P=0.000) and homozygous models (OR=1.54, 95% CI: 1.25–1.89, P=0.000), while weak correlation with PD susceptibility under the recessive (OR=1.25, 95% CI: 1.09–1.43, P=0.001), dominant (OR=1.41, 95% CI: 1.21–1.63, P=0.001) and heterozygous model(OR=1.30, 95% CI: 1.06–1.60, P=0.012). In the East Asian group, there was no relationship between rs3857059 and PD susceptibility under all models(P>0.05). European carrying rs356186 reduced risk of PD under the allelic (OR=0.78, 95% CI :0.71–0.86, P=0.000), homozygous (OR=0.66, 95% CI: 0.49–0.88, P=0.006), heterozygous (OR=0.78, 95% CI: 0.64–0.95, P=0.012), dominant (OR=0.76, 95% CI: 0.67–0.85, P=0.000) and recessive model (OR=0.71, 95% CI: 0.53–0.96, P=0.025). Rs3857059 was significantly relevant with the greater risk under allelic, dominant and heterozygous models (OR=1.47-1.50, P=0.000), while weak correlation with PD susceptibility under the recessive (OR=2.09, 95% CI: 1.08–4.03, P=0.028) and homozygous model (OR=2.22, 95% CI: 1.15–4.28, P=0.018). Rs2736990 was significantly associative with the larger PD susceptibility under five models (OR=1.27-1.66, P=0.000). In the Latino group, rs2736990 augmented the risk of PD under allelic (OR=1.74, 95% CI: 1.17–2.60, P=0.007), recessive (OR=2.54, 95% CI: 1.39–4.64, P=0.000) and homozygous model (OR=2.66, 95% CI: 1.44–6.20, P=0.024), while no correlation with PD susceptibility under dominant and heterozygous models (P>0.05). Rs3857059 added the risk of PD under allelic (OR=1.52, 95% CI: 1.06–2.19, P=0.023), dominant (OR=1.79, 95% CI: 1.01–3.16, P=0.046) and homozygous model (OR=2.40, 95% CI: 1.12–5.14, P=0.024), while no interrelation with PD susceptibility under recessive and heterozygous models (P>0.05).