PAX7 and osteogenesis imperfecta: In OI versus CTRL males, PAX7 staining showed a reduction in the number of MuSCs per mm2 in the TA at 10 days (−30%, p = 0.0134), 4 weeks (−43%, p = 0.0075) and 16 weeks (−56%, p < 0.0001) in the OI groups (Figure 1A).