A-F Proliferation assays examined proliferating (PAX7+MyoD+, arrows), self-renewing (PAX7+ MyoD−, open arrows), and differentiating (PAX7− MyoD+, arrowheads) cells from D233E patients (n = 2), healthy controls (n = 3) and disease controls (n = 3) at 1, 4, and 8 days growing in proliferation medium. (A) shows representative images from day 8. The number of patientmyoblasts is lower than that of controls at all three time points, indicating a slower proliferation rate in patientmyoblasts (B), and accordingly, the percentage of proliferating cells (C) is smaller in the patient. (D) The percentage of self-renewing cells is small in patient´s culture, reflecting a poor capacity for maintaining the pool of quiescent SCs. In addition, the percentage of PAX7+ cells (E) is smaller in patient´s culture, similarly to what was found in adult D233E muscle (shown in Fig 5D). (F) The percentage of differentiating cells is higher in the patient. We examine proliferation capturing 7-12 randomly fields per day and condition (mean ± SEM is shown; Kruskal-Wallis with Dunn´s multiple comparisons test; Scale bar, 50 µm). 