C9orf72 and frontotemporal dementia: Frontotemporal dementia (FTD), a common form of early-onset dementia, has an autosomal dominant inheritance in 20%–30% of patients, most often due to mutations in granulin (GRN), chromosome 9 open reading frame 72 (C9orf72) or microtubule-associated protein tau (MAPT).1 Developing sensitive biomarkers to detect disease onset at an early, even preclinical stage is of utmost importance for upcoming therapeutic interventions.