DMD and Duchenne muscular dystrophy: To assess whether our new non-invasive in vitro assay could be applied to other DMD patients with various mutations in the DMD gene in a hotspot region, specifically from exon 45 to 55 where DMD-causing deletion mutations accumulate21–23, we collected urine and cultured primary UDCs from three DMD patients with exon 50, 51, or 54 deletions (DMD-3, 4, and 5 in Table 1).