Thioflavin-S histochemistry of leptomeningeal vessels. Whole mounts of leptomeningeal vessels stained by thioflavine-S demonstrating amyloid angiopathy among the different PSEN mutations. A) PSEN1 M146L: moderate; B) PSEN1 V261I: severe; C) PSEN2 N141I: severe. D) PSEN1 V261F: severe; E) PSEN1 A431E: severe; F) PSEN1 Y115C: moderate; G) PSEN1 F105L: severe and H) PSEN1 A260V: moderate-severe. The remaining two PSEN1 mutations A79V and P264L had a mild amyloid deposition (data not shown). Scale Bars = 500 μm.