Overall, this meta-analysis displays that the frequency of the APOE ε4 allele is higher in AD than in the healthy controls and established a statistically significant association among risk factor APOE ε4 allele carriers and AD in the Italian population (OR = 3.60, 95% CI [2.90–4.47], p < 0.0001) (Figure 5). The gene discussed is APOE; the disease is Alzheimer disease.