C9 and frontotemporal dementia: To our knowledge, our study is the second to report on soluble and insoluble fractions of poly-GP and poly-GA [13] and the first one on soluble and insoluble poly-GR in different brain areas of human C9-FTD, providing insights into the solubility, distribution and abundance of the sense dipeptide repeat proteins poly-GA, poly-GP and poly-GR in relation to clinically affected and less affected areas.