In an initial attempt to find alternative exons that could serve as useful markers for splicing correction analyses in DM1 cells, we examined roughly 20 alternatively spliced transcripts known to be sensitive to MBNL level, and ∼20 transcripts regulated by other splicing factors either affected in DM1 (CUGBP1) or not affected in DM1 (PTBP1, PTBP2, NOVA1 and FOX2—used as the negative controls). The gene discussed is PTBP1; the disease is myotonic dystrophy type 1.