Thirty-seven patients (34.25%) were APOE ε4 carriers: SCD were less frequently APOE ε4 carriers (18.18%) when compared to MCI (46.15%, χ2 6.91, p = 0.009, Cramer’s V 0.285) and to AD (60.86%, χ2 10.75, p = 0.001, Cramer’s V 0.438). The gene discussed is APOE; the disease is Schnyder corneal dystrophy.