This contributes to a mild DMD phenotype due to a lower sensitivity to proteolysis and a reduced activation of TGF-β as it occurs in the human IAAM haplotype [16]; D2.B10-Dmdmdx/J (hereafter referred to as D2.B10) have a 12-amino-acid deletion in the same Ltbp4 region and functionally resemble the human VTTT haplotype (severe DMD phenotype due to increased sensitivity to proteolysis and increased TGF-β activity) [16]. The gene discussed is LTBP4; the disease is Duchenne muscular dystrophy.