Pedigrees of the Arctic AD families (a and b) and basic pathology in Sw2 patient (c-e). a and b: Pedigrees of the Swedish and American families with the Arctic AβPP gene mutation. Diagonal lines indicate deceased individuals; filled symbols indicate affected and open symbols unaffected members. The patients examined in this study in Family a are: IV:10 = Sw1, IV:29 = Sw2 and in Family b: III:1 = Am1, IV:1 = Am2. c: Sw2 patient’s brain weighed 1490 g. The gyri are only mildly atrophic, whereas the atrophy of hippocampus (arrow) and the dilatation of the ventricular system (asterisks) are obvious. d and e: Semi-consecutive sections from Sw2 patient’s frontal cortex: d: The plaques (five marked with an arrow) are discernible already with H&E staining. They are rounded, compact, eosinophilic structures with homogeneous texture, reminiscent of so called cotton wool plaques . Inset in d: Both pial and penetrating arteries are strongly Congo positive, but no plaques are visible. e: In a Bielschowsky silver impregnated section several plaques are vaguely ring formed (four marked with an arrow). No prominent dystrophic neurites are seen, only short, thin stubs. Inset (the square in e): Occasional plaques harbour somewhat coarser dystrophic neurites (arrow). Open arrow points to a neuron with neurofibrillary tangle. (bar in d 100 μm for d and e; bar in inset of e 40 μm).