In patients with active (symptomatic) MM, fluorescence-activated cell sorting (FACS) analysis on freshly isolated BM mononuclear cells revealed higher percentages of CD68+ macrophages (a glycoprotein expressed only by human macrophages) than in patients with nonactive disease (i.e., in partial/complete remission, or in plateau phase) or those with monoclonal gammopathies of undetermined significance (MGUS). This evidence concerns the gene CD68 and Miyoshi myopathy.