For instance, levels of two inflammatory mediators - platelet-derived growth factor BB, which is crucial for skeletal muscle regeneration through the stimulation of satellite cells and myoblasts (Scully et al., 2018; Scully et al., 2019), and neutrophil-derived myeloperoxidase-are significantly decreased in the serum of patients with physical frailty and sarcopenia, indicating immunosenescence and reduced muscle regenerative capacity (Calvani et al., 2020). The gene discussed is MPO; the disease is sarcopenia.