ACVRL1 and Alzheimer disease: Although arteriolar wallsin the hippocampal leptomeninges seem to exhibit weakened ALK1 immunoreactivity in ADpatients (BBIV-V, CDR1–2) versus non-AD subjects (BBIII, CDR0-0.5) (Fig. 3E,F), quantitativecomparison showed that only parenchymal and not leptomeningeal arteriolar walls undergosignificant reduction in ALK1 signal in AD patients (Fig.4C,D).