We selected plasma p-tau217 because previous findings in sporadic AD have suggested that CSF and plasma levels of p-tau217 might more accurately reflect AD pathology than p-tau181.17,19,20,21 We further measured plasma glial fibrillary acidic protein (GFAP), a marker of astrogliosis, which like p-tau217 has not been previously studied in DS. The gene discussed is GFAP; the disease is Alzheimer disease.