Plasma phosphorylated-tau217 is increased in Niemann-Pick disease type C.

Niemann-Pick disease type C and Alzheimer's disease are distinct neurodegenerative disorders that share the presence of neurofibrillary tangle pathology. In this multicentre study, we measured plasma phosphorylated-tau217 in controls (n = 60), Niemann-Pick disease type C (n = 71) and Alzheimer's disease (n = 30 positive for amyloid and negative for tau in CSF [A⁺T^-] and n = 30 positive for both [A⁺T⁺]). Annual Severity Increment Score and Lysotracker measurements were evaluated in the Niemann-Pick disease type C group to estimate the rate of progression and lysosomal enlargement, respectively. In the cross-sectional analysis, plasma phosphorylated-tau217 was increased in Niemann-Pick disease type C compared with controls (2.52 ± 1.93 versus 1.02 ± 0.34 pg/mL, respectively, P < 0.001) and inversely correlated with age at disease onset (R = -0.54, P < 0.001). In the longitudinal analysis, plasma phosphorylated-tau217 was associated with disease progression determined by Annual Severity Increment Score (R = 0.48, P < 0.001) and lysosomal enlargement (R = 0.26, P = 0.004). We found no differences between A⁺T^- Alzheimer's disease and Niemann-Pick disease type C (2.67 ± 1.18 versus 2.52 ± 1. 93 pg/mL, P = 0.31); however, A⁺T⁺ Alzheimer's disease had significantly higher levels than Niemann-Pick disease type C (3.26 ± 1.36 versus 2.52 ± 1.93 pg/mL, P = 0.001). Our findings suggest that plasma p-tau217 can increase in brain disorders with isolated tau pathology. Plasma p-tau217 associations with disease progression and severity make it a potential marker in Niemann-Pick disease type C.