On December 11, 2025, Rhythm Pharmaceuticals, Inc. (RYTM) disclosed positive preliminary results from a Phase 2 trial of its drug setmelanotide in patients with Prader-Willi syndrome (PWS). The 8-K filing reported that 6 out of 8 patients showed reductions in body mass index (BMI) from baseline after three months of treatment, according to the company's press release attached as Exhibit 99.1.

The company stated that David Meeker, Chairman, President & Chief Executive Officer, presented the results, which also included BMI reductions in patients after both three and six months of treatment. Rhythm Pharmaceuticals plans to complete the six-month data readout in 2026 and submit the full results for presentation at a medical conference, according to the filing.

In addition to the setmelanotide data, Rhythm Pharmaceuticals announced the initiation of Part D in a Phase 1 study to evaluate RM-718, another investigational drug for Prader-Willi syndrome. The company anticipates starting the first patient screening for RM-718 in December 2025, with the primary endpoint being evaluation of safety and tolerability.

The filing indicates that Jennifer Miller, Professor of Pediatric Endocrinology at the University of Florida, discussed the clinical results. Rhythm Pharmaceuticals' strategic plans include advancing setmelanotide into a Phase 3 registrational trial for Prader-Willi syndrome in 2026, based on the Phase 2 findings.