Plasma amyloid beta ratios in autosomal dominant Alzheimers disease: the influence of genotype
In-vitro studies of autosomal dominant Alzheimers disease (ADAD) implicate longer A{beta} peptides in pathogenesis, however less is known about the behaviour of ADAD mutations in-vivo. In this cross-sectional cohort study, we used liquid chromatography-tandem mass spectrometry to analyse 66 plasma samples from ADAD family members who were at-risk of inheriting a mutation or were already symptomatic. We tested for differences in plasma A{beta}42:38, 38:40 and 42:40 ratios between Presenilin1 (PSEN1) and Amyloid Precursor Protein (APP) carriers. We examined the relationship between plasma and in-vitro models of A{beta} processing and, among PSEN1 carriers, tested for associations with parental age at onset (AAO). 39 participants were mutation carriers (28 PSEN1 and 11 APP). Age- and sex-adjusted models showed marked differences in plasma A{beta} between APP and PSEN1: higher A{beta}42:38 in PSEN1 versus APP (p<0.001) and non-carriers (p<0.001); higher A{beta}38:40 in APP versus PSEN1 (p<0.001) and non-carriers (p<0.001), while A{beta}42:40 was higher in APP and PSEN1 compared to non-carriers (both p<0.001). A{beta} profiles were reasonably consistent in plasma and cell lines. Within PSEN1, sex-adjusted models demonstrated negative associations between (i)A{beta}42:40 (ii)A{beta}42:38 and parental AAO. In-vivo differences in A{beta} processing between APP and PSEN1 provide insights into ADAD pathophysiology which can inform therapy development.