Clinical Manifestations

In autosomal dominant Alzheimer's disease (ADAD), mutations in APP, PSEN1 and PSEN2 alter amyloid-β processing, driving production of longer, aggregation-prone amyloid-β petides that deposit in parenchyma as plaques and blood vessel walls as cerebral amyloid angiopathy (CAA). However, different mutations vary in the amyloid-β isoforms produced, the type and severity of amyloid-β plaques and CAA, and clinical manifestations. As CAA is a risk factor for amyloid-related imaging abnormalities (ARIA) during anti-amyloid-β immunotherapy, investigating relationships between clinical, genetic and neuropathological heterogeneity may have relevance for understanding the natural history of the disease and responses to therapy.

50 individuals with ADAD underwent post-mortem brain donation to the Institute of Psychiatry or Queen Square Brain Bank (QSBB); 37 with PSEN1 mutations, 13 with APP. Clinical phenotype data were reviewed and frontal cortex sections stained immunohistochemically with a pan amyloid-β antibody. Blood vessel counts were used to determine the frequency and severity of CAA in leptomeninges and parenchyma. The 29 QSBB cases were also stained using a lecanemab-biosimilar antibody (lecanemab-BS), and immunofluorescence co-staining was carried out for lecanemab-BS, amyloid-β₄₀, amyloid-β₄₂ and amyloid-β₄₃. 10 of these individuals had undergone MRI including susceptibility-weighted imaging (SWI) sequences during life. Relationships between clinical, imaging and neuropathological features were explored.

Non-amnestic cognitive presentations and atypical clinical features (pyramidal, extrapyramidal and cerebellar signs) were more common with PSEN1 than APP mutations. All cases demonstrated end-stage AD pathology, however the frequency and severity of CAA varied considerably. Lecamemab-BS labelled amyloid-β plaques (diffuse and dense-core) in all cases, and extensively labelled amyloid-β in blood vessels when CAA was present. More severe CAA was associated with greater lecanemab-BS binding. Four of the 10 individuals with SWI had one to three microbleeds on MRI. These four all had moderate-severe CAA post-mortem, however, so did five of those without microbleeds.

Lecanemab-BS bound to amyloid-β plaques and CAA in cases of ADAD with a variety of mutations and clinical features. The increased lecanemab binding in blood vessels with more severe CAA highlights the need for more sensitive biomarkers of CAA during life and provides further incentive for treating early in the disease.