The endoplasmic reticulum stress marker GORASP2 increased over time in DMD-COs, while ARCN1 was more prominent in DMD-COs, but they were not co-localized with NKX2.5, suggesting other cell type than differentiating cardiomyocytes experienced high ER stress within the generated DMD-COs and DMD-Iso-COs. The gene discussed is DMD; the disease is Duchenne muscular dystrophy.