Consistent with an important role of denervation in COPD muscle, a recent study found significant correlations between circulating biomarkers of denervation (e.g., cleaved agrin fragment 22, brain derived neurotrophic factor) and the presence of muscle atrophy in male COPD patients (Karim et al., 2021). The gene discussed is BDNF; the disease is chronic obstructive pulmonary disease.