APP and cerebral amyloid angiopathy: Whit regard to HCHWA-D (a syndrome of primarily hemorrhagic strokes and dementia), it is caused by a mutation in the gene for amyloid precursor protein (APP) that causes abnormal deposition of amyloid in the walls of leptomeningeal arteries and cortical arterioles (a mpathological condition known as cerebral amyloid angiopathy [CAA]).