\nMirum Pharmaceuticals, Inc. (NASDAQ: MIRM), a leading rare disease company, today announced positive results from Cohort 2 of the pivotal PROGRESS study of ATEBRIOZ\u2122<\/b> (zilurgisertib), an oral activin receptor-like kinase 2 (ALK2) inhibitor, in pediatric patients aged 6 to <12 years with fibrodysplasia ossificans progressiva (FOP). At Week 24, zilurgisertib reduced total heterotopic ossification (HO) lesion volume and improved clinician-assessed joint mobility. No zilurgisertib-treated patients developed new HO lesions.<\/p>\n
\nThe results build on data from PROGRESS Cohort 1, which supported the U.S. Food and Drug Administration (FDA) approval of ATEBRIOZ in September 2026 for adult and pediatric patients aged 12 years and older with FOP. Mirum plans a supplemental New Drug Application (sNDA) submission in H1 2027 to expand the indication to pediatric patients aged 6 to <12 years.<\/p>\n
\n\u201cThese results represent an important advance for younger children living with FOP,\u201d said Rob Myers, M.D., Chief Medical Officer of Mirum. \u201cThe reduction in total HO volume and absence of new lesions seen with zilurgisertib build on the positive results previously observed in adolescents and adults in Cohort 1 of PROGRESS. We look forward to discussing these findings with the FDA to expand access to ATEBRIOZ for younger children living with this debilitating disease.\u201d<\/p>\n
\n\u201cFOP is a devastating genetic disease that leads to progressive loss of mobility, independence, quality of life, and shortened lifespan,\u201d said Frederick S. Kaplan, M.D., Isaac and Rose Nassau Professor of Orthopaedic Molecular Medicine at the University of Pennsylvania Perelman School of Medicine. \u201cChildhood is a critical window in FOP, so a therapy targeting the underlying cause of the disease is especially important for this young age group. Results such as these offer hope that we may be able to slow disease progression in children before its most serious consequences arise.\u201d<\/p>\n
PROGRESS Cohort 2 Results<\/b><\/p>\n
\nCohort 2 of the PROGRESS study enrolled 25 pediatric patients aged 6 to <12 years with FOP. Patients were randomized 1:1 to receive once-daily oral zilurgisertib 75 mg (n=12) or placebo (n=13) during a 24-week double-blind period, followed by an open-label extension. The mean age at baseline was 8.3 years, with a mean of 5.0 years since initial diagnosis. All patients completed the double-blind period and entered the open-label extension.<\/p>\n
\nAt Week 24, mean total HO lesion volume decreased by 8.09 cm\u00b3 in patients receiving zilurgisertib, compared with an increase of 9.14 cm\u00b3 in patients receiving placebo (nominal p=0.003). No zilurgisertib-treated patients developed new HO lesions.<\/p>\n
\nImprovements in clinician-assessed joint mobility were also observed. Joint mobility was assessed using the Cumulative Analogue Joint Involvement Scale (CAJIS), a validated measure of physical function in FOP scored from 0 (no impairment) to 30 (maximum impairment). At Week 24, CAJIS scores improved by a mean of 0.80 points in patients receiving zilurgisertib, compared with 0.09 points in patients receiving placebo. In untreated patients with FOP, CAJIS scores are reported to worsen by approximately 0.5 points per year.1<\/sup> Key efficacy data from Cohort 2 are shown below in the Efficacy Results<\/b> table.<\/p>\n Efficacy Results<\/b><\/p>\n
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