Because exosomal clusterin is elevated in tauopathies, the ratio of α‐synuclein to clusterin improved the diagnostic value of the test specifically in differentiating neuronal synucleinopathy from tauopathy across cohorts with an AUC of 0.98 versus 0.99, sensitivity of 0.93 versus 1, and specificity of 0.98 versus 0.95 when using a cutoff of (α‐Syn/Clu) × 1000 = 1.1. This evidence concerns the gene CLU and tauopathy.