A form of hereditary cerebral hemorrhage with amyloidosis characterized by an age of onset of 45 years of age, progressive Alzheimer's disease-like dementia, and lobar intracerebral hemorrhage in some patients. This subtype is due to a mutation in the <i>APP</i> gene (21q21.2), encoding the beta-amyloid precursor protein. This mutation causes an increased accumulation of amyloid-beta protein in the walls of the arteries and capillaries of the meninges, cerebellar cortex and cerebral cortex, leading to the weakening and eventual rupture of these vessels. [from ORDO]