APOE and Alzheimer disease: No significant differences were found between any subgroups, for any comparisons: we analyzed age, gender, expanded disability status scale (EDSS) and disease duration when looking at PPMS outliers in AD or HA; age, gender, APOE4 and MMSE score when looking at HA outliers in PPMS; age, gender, years of education, MMSE, ADAS-Cog, APOE4, CDRSB, AV45, when looking at AD outliers in PPMS.