PSMB9 and dermatomyositis: Similarly, in idiopathic inflammatory myopathies (IIMs), such as polymyositis and dermatomyositis, disorders characterized by immune-mediated muscle damage, akin in part to sarcopenia, there is constitutive overexpression of IMP subunits β1i (LMP2), β2i (MECL1), and β5i (LMP7) in affected muscle tissue [28,29].