C9orf72 and amyotrophic lateral sclerosis: However, both studies chose to measure poly(GP) for several reasons: (i) poly(GP) is one of the most frequent DPRs in C9FTD/ALS central nervous system (CNS) tissue; (ii) it is more soluble than poly(GA), which is the most frequent DPR; (iii) it appears to be a highly stable DPR, as demonstrated by its persistence in cultured iPSC‐derived neurons (Gendron et al, 2017); and (iv) it is produced from both sense and antisense C9orf72 transcripts, although it is worth noting that ASO studies suggest sense transcripts are the major origin.