Blood phosphorylated tau elevation as a biomarker in immunoglobulin light chain and transthyretin amyloidosis.

Elevated blood levels of phosphorylated tau (p-tau) are diagnostic of Alzheimer disease and are associated with the deposition of amyloid-β in the cerebral neuropil. Elevated p-tau levels have also been associated with cerebral deposition of Danish amyloid and prion protein amyloid. Here we analyzed p-tau in serum from four different cohorts of people with the most common types of systemic amyloidosis, transthyretin (ATTR) amyloidosis and immunoglobulin light chain (AL) amyloidosis. We found higher levels of serum p-tau181 in the AL and ATTR groups than in controls. Subsequent analyses revealed that these effects were more pronounced in the presence of polyneuropathy (PNP) and in AL compared to ATTR amyloidosis. Individuals with different forms of PNP that were not due to amyloidosis did not exhibit elevated p-tau181 levels. In cases of presymptomatic (genetic) ATTR, p-tau181 levels increased as a function of predicted years from symptom onset. Additional measurement of p-tau217 in one cohort revealed similar increases, and discriminated people with AL and those with ATTR from controls equally as well as p-tau181. These findings suggest that elevated serum p-tau levels are not specific to Alzheimer disease and may also serve as a diagnostic tool of ATTR and AL amyloidosis, with potential utility in distinguishing amyloidosis-related PNP from PNP of other etiologies.