C9orf72 and frontotemporal dementia: We next investigated poly-PG, which is less toxic than poly-PR (Wen et al., 2014; Lee et al., 2016; Mizielinska et al., 2014; Freibaum et al., 2015), and has been proposed as a biomarker for C9ORF72-ALS/FTD (Gendron et al., 2017; Lehmer et al., 2017).