Statistical significance was not found between the Parkin heterozygotes and Parkin homozygotes/compound heterozygotes due to the small number of heterozygotes, but the mean olfaction score of heterozygotes was lower than that of the patients in group II, which was consistent with previous reports that heterozygous Parkin mutations is regard as risk factors of PD (Alcalay et al., 2011; Malek et al., 2016). This evidence concerns the gene PRKN and Parkinson disease.