SPP1 and Duchenne muscular dystrophy: To date, DNA polymorphisms encoding two components of the TGFβ cell repair and fibrosis pathway (osteopontin [SPP1 gene], latent TGFβ-binding protein 4 [LTBP4 gene]), an inflammatory protein (CD40) and a loss-of-function polymorphism of α-actinin 3 (ACTN3 gene) have been found to be associated with DMD severity and response to steroids (5–9).