DS cohorts with available CSF are scarce and current biofluid markers for AD in the DS population are restricted to surrogate markers of amyloidosis (CSF Aβ1–42 or amyloid PET tracers) and tau-mediated neurodegeneration (CSF p-tau and t-tau) combined with neuropsychological assessment, which can be confounded by substantial inter-individual variation in intellectual disability. Here, MAPT is linked to amyloidosis.