HNMT and Parkinson disease: The present systematic review and meta-analysis, which included 4 studies involving 2108 patients with PD and 2158 controls, showed a significantly lower frequency of patients carrying the minor allele of the HNMT rs11558538 SNP in patients with PD than in controls, both in the allele positivity analysis and in the comparison of minor allele frequencies, whereas the association of HNMT rs11558538TT homozygosity with PD risk did not reach statistical significance because of the low frequency of the homozygous genotype.