APOE and early-onset autosomal dominant Alzheimer disease: Indigenous ancestry and Alzheimer’s disease risk associations suggested some protective benefits,105 whereas African ancestry was associated with increased risk.103 Single-nucleotide polymorphisms and haplotypes in various genes were associated with Alzheimer’s disease risk and protection, with differences noted between Europeans and a Brazilian cohort.104 Although the APOE ε4 is a key risk factor for Alzheimer’s disease in various populations, the role of other genetic factors remains unclear.