APOE and Parkinson disease: In the other study, epistasis analysis was performed between APOE haplotypes and haptoglobulin gene (HP) functional polymorphisms, with HP *1/*1 genotype protecting APOE ε4-carriers from age-related negative selection; in light of these results, the authors called for further research on APOE/HP interactions in age-related diseases such as Alzheimer’s and Parkinson’s disease [24].