(ii) DMD patients treated with ACE-031, a soluble form of activin type IIB receptor, showed a very slight increase in total body lean mass (+4.1% compared with +2.6% in the placebo group) and a non-statistically significant trend for maintenance of 6 min walk test was observed in the ACE-031 treated group, although the study had to be interrupted after 12–16 weeks due to safety concerns9. Here, ACVR2B is linked to Duchenne muscular dystrophy.