NEFL and Alzheimer disease: Positron emission tomography (PET) imaging studies have revealed that increased regional binding of Aβ and tau radiotracers is similar in both DS and AD.4,5,6 Cerebrospinal fluid (CSF) biomarkers of AD-related brain Aβ pathology (Aβ42/40), tau pathology (phosphorylated tau [p-tau]), and neurodegeneration (neurofilament light [NfL]) have shown promise as diagnostic and prognostic biomarkers of AD in DS.7,8 However, for implementation in clinical practice and drug trials, inexpensive, noninvasive, scalable, and easily accessible blood biomarkers are needed.