US FDA approves Regeneron's rare bone disorder drug. Regeneron's Pasatru has received US FDA approval for adults with FOP after clinical trials showed a significant reduction in abnormal bone formation. By Reuters August 20, 2026, 8:59:40 AM IST (Published) The US FDA on Wednesday (August 19) approved Regeneron's drug for a rare genetic disorder after it significantly reduced abnormal bone formation in certain soft tissues. New York-based Regeneron's shares rose 4%. The drug, garetosmab, branded as Pasatru, was approved to treat adults with fibrodysplasia ossificans progressiva (FOP) - a condition in which muscle, tendon and ligament tissue gradually turns into bone, leading to a "second skeleton" that causes progressive loss of mobility and reduced life expectancy. In a 56-week trial involving 63 participants, Pasatru reduced the development of new bone abnormalities by 94% in patients treated with a 3 mg per kg dose and by 90% in those given a 10 mg per kg dose, compared with a placebo. The drug works by blocking Activin A, a protein involved in triggering abnormal bone growth in patients with FOP. Susan Rhee, a member of Regeneron's clinical team, told Reuters last week that the company plans to start a trial for children later this year. The drug will compete with French drugmaker Ipsen's oral treatment Sohonos, which in 2023 became the only other treatment approved by the US Food and Drug Administration. Incyte and partner Mirum Pharma, as well as privately held Ashibio, are also developing treatments for the condition. In 2020, Regeneron paused dosing in a mid-stage trial of the drug after five patient deaths, ultimately discontinuing the study and working with global regulators to design the late-stage trial, according to the company. The condition affects roughly 1 in 2 million people worldwide, with around 800 to 900 active diagnosed cases globally, according to data from the National Institutes of Health.

Mirum Pharmaceuticals shares plunged 15% on Thursday after the FDA recommended an additional Phase 3 study for its liver disease candidate Volixibat, potentially delaying the new drug application until the first half of 2027. Citizens lowered its price target to $137 from $146 whilst maintaining an Outperform rating. The regulatory setback overshadowed strong second-quarter results. Mirum reported revenue of $176.2 million, beating analysts' estimates of $167.3 million. The company raised its full-year net product sales guidance to $680 million to $700 million, from $660 million to $680 million. Mirum ended the quarter with $561.3 million in cash and equivalents. Volixibat has already received FDA Breakthrough Therapy and Orphan Drug designations.