The prevalence of Clock T3111C and Per2 C111G polymorphisms did not significantly differ between SCD and MCI (Clock T3111C: 51.2% in SCD and 40.7% in MCI; Per2 C111G: 19.5% in SCD and 18.5% in MCI); moreover, there were not any differences in the prevalence of both Clock C and Per2 G carriers in SCD and MCI groups. This evidence concerns the gene PER2 and Schnyder corneal dystrophy.