NOS1 and Parkinson disease: This is not unreasonable because the key benefit of the meta-analysis from the aggregation of information is to increase the estimator accuracy, shorten the CIs, and thus improve the statistical power to provide a better estimation, which may depart from the assessment acquired from any included study.[51] However, more studies with large sample sizes are required to verify the association of NOS1 exon18 variant, especially the heterozygous TC genotype with PD risk in the future.