About three months after taking the wraps off a $41 million mezzanine financing, Rhythm Pharmaceuticals Inc. is kicking off a pivotal trial of its lead candidate, setmelanotide, for an ultra-rare genetic obesity disorder. The melanocortin-4 (MC4) receptor agonist will be tested in an open-label, single-arm phase III study evaluating its efficacy for the treatment of pro-opiomelanocortin (POMC) deficiency obesity, a condition estimated to affect between 100 and 500 patients in the U.S.