SPP1 and muscular dystrophy: Genetic modifiers on the DBA/2 genetic background, including osteopontin (Spp1), synonymous variant in Annexin A6 (Anxa6) exon 1, and polymorphisms in the coding region of the latent TGF-β-binding protein 4 gene (Ltbp4), generate a more severe muscular dystrophy mouse model (Heydemann et al., 2009; Quattrocelli et al., 2017; Swaggart et al., 2014).