Rhythm Pharmaceuticals Inc. said its investigational drug setmelanotide helped patients with certain rare genetic disorders of obesity lose weight in midstage trials.

Setmelanotide works by activating the melanocortin 4 receptor, or MC4R, a protein that plays a role in regulating energy expenditure and appetite.

The phase 2 basket studies evaluated setmelanotide in patients with rare genetic obesity disorders such as Bardet-Biedl syndrome, or BBS; Alström syndrome; pro-opiomelanocortin, or POMC, and other MC4 heterozygous deficiency obesities; and proopiomelanocortin epigenetic disorders.

For the five patients with BBS, the drug helped them achieve an average of 18.5% weight loss and cut their average hunger score by 74.2% after 40 to 60 weeks of treatment. The company noted that one pediatric patient with type 1 diabetes had no body weight change but had an average hunger score decrease of 53.3% and improved average blood sugar level to 7.6% from 10.1%.

For the Alström syndrome patient group, one patient achieved 23.2% weight loss and had 45.5% reduction in hunger score after 38 weeks of treatment.

In the POMC and other MC4 heterozygous deficiency obesity group, two patients lost weight by 15.4% and 6.5%, respectively. The first patient's hunger score decreased by 80%, while the second patient was at 20%.

Furthermore, the patient with POMC epigenetic disorder showed a 60% decrease in hunger score in the titration phase and withdrew from the treatment after a four-week vacation. The patient has resumed treatment and lost weight by a total of 9.2% over the trial.

The Boston-based biopharmaceutical intends to hold discussions with the U.S. Food and Drug Administration regarding the final design, protocol and goals of a combined phase 3 study for setmelanotide in patients with BBS and Alström syndrome, which it plans to conduct by the end of 2018.