Amyloid fibrils in FTLD-TDP are composed of TMEM106B and not TDP-43

Frontotemporal lobar degeneration (FTLD) is the third most common neurodegenerative condition after Alzheimer’s and Parkinson’s diseases¹. FTLD typically presents in 45 to 64 year olds with behavioural changes or progressive decline of language skills². The subtype FTLD-TDP is characterized by certain clinical symptoms and pathological neuronal inclusions with TAR DNA-binding protein (TDP-43) immunoreactivity³. Here we extracted amyloid fibrils from brains of four patients representing four of the five FTLD-TDP subclasses, and determined their structures by cryo-electron microscopy. Unexpectedly, all amyloid fibrils examined were composed of a 135-residue carboxy-terminal fragment of transmembrane protein 106B (TMEM106B), a lysosomal membrane protein previously implicated as a genetic risk factor for FTLD-TDP⁴. In addition to TMEM106B fibrils, we detected abundant non-fibrillar aggregated TDP-43 by immunogold labelling. Our observations confirm that FTLD-TDP is associated with amyloid fibrils, and that the fibrils are formed by TMEM106B rather than TDP-43.