Testing the causal impact of amyloidosis on total Tau using a genetically informative sample of adult male twins.

Abstract

INTRODUCTIONThe amyloid cascade hypothesis predicts that amyloid-beta (A{beta}) aggregation drives tau tangle accumulation. We tested competing causal and non-causal hypotheses regarding the direction of causation between A{beta}40 and A{beta}42 and total Tau (t-Tau) plasma biomarkers. METHODSPlasma A{beta}40, A{beta}42, t-Tau, and neurofilament light chain (NFL) were measured in 1,035 men (mean = 67.0 years) using Simoa immunoassays. Genetically informative twin modeling tested the direction of causation between A{beta}s and t-Tau. RESULTSNo clear evidence that A{beta}40 or A{beta}42 directly causes changes in t-Tau was observed; the alternative causal hypotheses also fit the data well. In contrast, exploratory analyses suggested a causal impact of the A{beta} biomarkers on NFL. Separately, reciprocal causation was observed between t-Tau and NFL. DISCUSSIONPlasma A{beta}40 or A{beta}42 do not appear to have a direct causal impact on t-Tau. In contrast, A{beta} aggregation may causally impact NFL in cognitively unimpaired men in their late 60s.