Human iPSC lines derived from individuals with DM1 and controls have been previously characterized elsewhere (10 (link), 11 (link)). DM1 iPSCs were provided as a gift from the Gottesfield laboratory at the Scripps Institute, whereas control lines were a gift from the Goldstein laboratory at University of California San Diego (UCSD). iPSC colonies were expanded on Matrigel-coated dishes (BD Biosciences) with mTeSR1 medium (STEMCELL Technologies). The cells were routinely checked by karyotype and copy number variation (CNV) arrays to avoid genomic alterations in the culture. Human embryonic kidney 293T cells were purchased from the American Type Culture Collection.