APOE and major depressive disorder: Our results imply that Parkinson’s disease patients with high genetic risk for Alzheimer’s disease, but excepting APOE, are more likely to develop a more aggressive form of Parkinson’s disease that includes dementia symptoms as indicated by Axis 1, which represents worsening non-tremor, motor phenotypes, anxiety and depression accompanied by a decline in cognitive function (Table 2 and Fig. 2).