PSEN1 and Alzheimer disease: For example, in the absence of a reliable family history, a retrospective cohort study of familial and non-familial early-onset Alzheimer's disease with the commonest PSEN1 mutation identified the following clinical characteristics as key features that may aid discrimination; an early and progressive age at onset, history of headaches, myoclonus, gait abnormalities and pseudobulbar affect.34