Blood-based assay for diagnosing and treating based on site-specific tau phosphorylation

A method to diagnose a subject as having an increased risk for conversion to mild cognitive impairment due to Alzheimer's disease prior to the onset of Alzheimer's disease, the method comprising

• (a) providing an isolated tau sample obtained from the subject, wherein the isolated tau sample is produced by
• precipitating proteins from a blood sample using perchloric acid, thereby producing an acid soluble extract of blood;
• and
• concentrating soluble tau in the acid soluble extract by solid phase extraction using a reversed-phase sorbent and affinity-purification using one or more epitope binding agent, wherein at least one epitope binding agent specifically binds an epitope within the N-terminus of tau or within the mid-domain of tau, and
• measuring by mass spectrometry an amount of tau phosphorylation at (i) T217 and T205, (ii) T181 and T205, or (iii) T181, T205 and T217;
• (b) diagnosing the subject as having an increased risk for conversion to mild cognitive impairment due to Alzheimer's disease when
• (1) tau phosphorylation at T217 or T181 is about 1.5σ or above and tau phosphorylation at T205 is about 1.5σ or less above the mean of a control population, where o is the standard deviation defined by the normal distribution of tau phosphorylation at T217 and T205, T181 and T205, or T181, T205 and T217 measured in a control population without brain amyloid plaques as measured by PET imaging and/or Aβ42/40 measurement in CSF;
• (2) the ratio of tau phosphorylation at T217 or T181 to total tau is above 20 and the ratio of tau phosphorylation at T205 to total tau is below 2σ, where σ is the standard deviation defined by the normal distribution of total tau and tau phosphorylation at T217 and T205, T181 and T205, or T181, T205 and T217 measured in a control population without brain amyloid plaques as measured by PET imaging and/or Aβ42/40 measurement in CSF;
• or
• (3) tau phosphorylation at (i) T217 and T205, (ii) T181 and T205, or (iii) T181, T205 and T217 is about 1.50 or above, where o is the standard deviation defined by the normal distribution of tau phosphorylation at T217 and T205, T181 and T205, or T181, T205 and T217 measured in a control population without brain amyloid plaques as measured by PET imaging and/or Aβ42/40 measurement in CSF.