APOE and synucleinopathy: Genome-wide association studies (GWAS) and meta-analyses have exposed the ε4 allele variant of the APOE gene (APOE ε4) as a contributing risk factor for increased rate of cognitive decline, worsened cognitive impairment and/or earlier onset of dementia in synucleinopathies with cognitive features [4, 9, 18, 21, 30, 34, 37–39, 41, 48, 49].