MSTN and Atrophy: ACVR2B, for which we found the strongest evidence for gene-based association (P=0.0002), encodes the principal transmembrane receptor of myostatin: the target of BYM338, a monoclonal antibody-based inhibitor of ActRIIB, which has shown early promise in reversing muscle atrophy and promoting hypertrophy in phase I trials45, 46.