A statistically significant difference in APOE ε4 allele distribution was found between groups (MCI vs AD β=-2.442 p=0.015; SCD vs AD β=-3.163 p=0.002, not between SCD vs MCI, p=0.214), as AD patients showed a higher ε4 allele percentage (33.3%) than MCI (23.6%) and SCD (15.4%). The gene discussed is APOE; the disease is Alzheimer disease.