A number of neuritic plaques with Alzheimer disease are seen here. They have an amyloid core as seen here with Congo red stain. Small peripheral cerebral arteries may also be involved. The Aß may be deposited in cortical vessels, principally small arteries and arterioles, leading to an amyloid angiopathy. These small vessels are prone to bleed. It is interesting to note that the gene coding for cerebral amyloid precursor protein (APP) is on chromosome 21--and persons with trisomy 21 living to age 40 invariably develop Alzheimer disease.