Modified amyloid variants in pathological subgroups of β‐amyloidosis

Objective: Amyloid β (Aβ) depositions in plaques and cerebral amyloid angiopathy (CAA) represent common features of Alzheimer's disease (AD). Sequential deposition of post‐translationally modified Aβ in plaques characterizes distinct biochemical stages of Aβ maturation. However, the molecular composition of vascular Aβ deposits in CAA and its relation to plaques remain enigmatic. Methods: Vascular and parenchymal deposits were immunohistochemically analyzed for pyroglutaminated and phosphorylated Aβ in the medial temporal and occipital lobe of 24 controls, 27 pathologically‐defined preclinical AD, and 20 symptomatic AD cases. Results: Sequential deposition of Aβ in CAA resembled Aβ maturation in plaques and enabled the distinction of three biochemical stages of CAA. B‐CAA stage 1 was characterized by deposition of Aβ in the absence of pyroglutaminated AβN3pE and phosphorylated AβpS8. B‐CAA stage 2 showed additional AβN3pE and B‐CAA stage 3 additional AβpS8. Based on the Aβ maturation staging in CAA and plaques, three case groups for Aβ pathology could be distinguished: group 1 with advanced Aβ maturation in CAA; group 2 with equal Aβ maturation in CAA and plaques; group 3 with advanced Aβ maturation in plaques. All symptomatic AD cases presented with end‐stage plaque maturation, whereas CAA could exhibit immature Aβ deposits. Notably, Aβ pathology group 1 was associated with arterial hypertension, and group 2 with the development of dementia. Interpretation: Balance of Aβ maturation in CAA and plaques defines distinct pathological subgroups of β‐amyloidosis. The association of CAA‐related Aβ maturation with cognitive decline, the individual contribution of CAA and plaque pathology to the development of dementia within the defined Aβ pathology subgroups, and the subgroup‐related association with arterial hypertension should be considered for differential diagnosis and therapeutic intervention