MAPT and early-onset autosomal dominant Alzheimer disease: Diagnosis and evaluation of patients with Niemann–Pick disease type C rely on clinical manifestations, family history and genetic analysis.3,26 However, easily accessible and reliable blood-based biomarkers that could be used to support diagnosis and monitoring of patients with Niemann–Pick disease type C are lacking.3,27 Moreover, understanding the complex interplay between tau pathology in Alzheimer’s disease and Niemann–Pick disease type C offers opportunities to gain new insights into the underlying mechanisms and potential strategies for lysosome and tau-targeting therapies.1,28-31