RFC1 and amyotrophic lateral sclerosis: To investigate whether AAGGG/CCCTT repeat expansions trigger RFC1 intron 2 stabilization as a circular lariat species, as may occur in C9orf72 FTD/ALS (44), we used whole-transcriptome RNA short read sequencing to map RFC1 mRNA splicing isoforms and identify the presence of intronic back-spliced reads indicative of circular mRNA species (circRNAs) arising from circular intronic lariats (50).