Although no connection was found in the heterozygous model (TC vs CC: OR = 1.11, 95%CI: 0.92–1.35, P = 0.27), NOS1 exon18 polymorphism was observed to be statistically significantly associated with the development of PD in other 4 genetic models (allelic T vs C: OR = 1.25, 95%CI 1.09–1.44, P = 0.001; homozygous TT vs CC: OR = 1.79, 95%CI 1.32–2.45, P < 0.001; recessive TT vs TC + CC: OR = 1.70, 95%CI 1.26–2.28, P < 0.001; dominant TT + TC vs CC: OR = 1.22, 95%CI 1.02–1.46, P = 0.03) (Table 3). Here, NOS1 is linked to Parkinson disease.