SSPN and limb-girdle muscular dystrophy: Consistent with these clinical observations, SSPN is absent from the sarcolemma of four different sarcoglycan-deficient murine models of LGMD (types R3, R4, R5, and R6) caused by mutations in genes encoding any one of the four canonical sarcoglycan proteins (α-, β-, γ-, and δ-sarcoglycan) [7,9,10,11].