CD40 and Duchenne muscular dystrophy: To date, single nucleotide polymorphisms (SNPs) in four genes, osteopontin (SPP1) [16,17,18], α-actinin-3 (ACTN3) [19], latent transforming growth factor binding protein (LTBP4) [18,20] and CD40 [21] have been identified as disease modifiers in DMD.