Alzheimer’s disease (AD) is the most common form of dementia, affecting 50 million people worldwide1 In vivo AD diagnosis and monitoring of treatment response in clinical trials is based on changes in amyloid beta proteins (Abeta), measured by positron emission tomography (PET) or in cerebrospinal fluid (CSF)2–4 However, both methods are associated with major disadvantages in terms of high costs (PET) and invasiveness (lumbar puncture to collect CSF), which prohibit repetitive analysis. This evidence concerns the gene APP and early-onset autosomal dominant Alzheimer disease.