Fig. 2

a Intron 1-retaining transcripts contain the G₄C₂ repeat sequence. PCR using primers spanning the G₄C₂ repeat region was performed on cDNA reversed transcribed from polyadenylated C9orf72 RNA from control and expansion carrier lymphoblasts. The two products of slightly different sizes detected in cells from normal individuals correspond to the two alleles; the single product generated from expansion carrier cells corresponds to the wild-type allele. b Intron 1-retaining transcripts are produced from both wild-type and mutant alleles. Sequence traces of C9orf72 overlapping the intron 1-exon 2 boundary and the rs10757668 SNP in cDNA (top panels) and genomic DNA (gDNA, bottom panels) prepared from lymphoblasts from two control individuals and two expansion carriers heterozygous for rs10757668. One of the control cases (top trace) is heterozygous for rs10757668. The sequence of the reverse strand is shown; the position of rs10757668 is indicated by the grey box. Intron 1-retaining transcripts contain both the C and T alleles showing that intron 1 retention occurs in RNA transcribed from the wild-type as well as the expanded allele. C9⁻, controls; C9⁺, expansion carriers