While joint amyloid and tau pathology, like in A+T+ Alzheimer’s disease, seem to have a stronger effect on levels of this marker in plasma, we showed that isolated amyloid pathology (A+T− Alzheimer’s disease) and isolated tau pathology (Niemann–Pick disease type C) have a similar effect on levels of p-tau217 in blood, suggesting that the elevation of p-tau217 can be associated with amyloid and tau pathology, and the mechanisms behind these increases could be more in relation to the dysregulation in the shared pathways between amyloid and tau (e.g. lysosomal clearance and lipid metabolism). The gene discussed is MAPT; the disease is early-onset autosomal dominant Alzheimer disease.