Of the studies included in this narrative review, Alzheimer’s disease pathology, including greater burden of amyloid plaques and neurofibrillary tau tangles, have been associated with greater loneliness even after controlling for other markers such as age, sex, and apolipoprotein E ε4, the genetic risk marker of Alzheimer’s disease [10,28,30]. This evidence concerns the gene APOE and early-onset autosomal dominant Alzheimer disease.