SSPN and sarcoglycanopathy: To investigate the effect of SSPN overexpression in the sarcoglycanopathies, we crossed α-, β-, and γ-SG–deficient mice with C57BL/6J WT SSPN transgenic mice in which the SSPN transgene is expressed under control of the human skeletal α-actin promotor (61), resulting in skeletal muscle–specific overexpression at threefold normal levels (Supplemental Figure 1; supplemental material available online with this article; https://doi.org/10.1172/JCI187868DS1).