OR29-05 A Natural History Study of Fibrodysplasia Ossificans Progressiva (FOP): 12-Month Outcomes

Background: FOP is an ultra-rare, severely disabling genetic disorder characterized by episodic flare-ups and heterotopic ossification (HO) leading to restricted movement, physical disability, and early death. FOP may initially be misdiagnosed in ~90% of individuals leading to unnecessary and often harmful interventions. Patients with FOP are diagnosed and managed by multiple specialties, including endocrinologists. Data from an ongoing, prospective, longitudinal, global, natural history study (NCT02322255) were used to investigate the progression of FOP, HO formation, and impact on physical functioning over time. We present results from the first 12 months of the 3-year study. Methods: Males and females with FOP and a documented ACVR1 R206H mutation participated. HO volume was assessed by low-dose whole body computed tomography (WBCT) scan, excluding the head. All imaging was interpreted at a blinded, central laboratory using pre-specified procedures. Functional outcomes were evaluated using the Cumulative Analogue Joint Involvement Scale (CAJIS; for each joint: score=0 represents <10% involvement, score=1 represents 10–90% involvement, and score=2 represents >90% ankylosed across 15 major joints; total score range 0 to 30 [higher scores indicate more severe mobility limitations]) and the FOP Physical Function Questionnaire (FOP-PFQ; percent total score). Changes from Baseline at Month 12 were evaluated for new HO volume, CAJIS, and FOP-PFQ. Results: Of 114 participants (pts) with Baseline data, 99 (4 to 56 years at enrollment; mean 17 years of age; 56% male) also had a Month 12 assessment. A total of 93 pts had evaluable WBCT scans at Baseline and Month 12 and were included in the HO analysis. In total, 40% (37/93) of pts had new HO over 12 months; the mean volume of new HO in these pts was 57,706 mm(3) (SD=100,079 mm(3); median=20,753 mm(3); range: 522 to 438,826 mm(3)). Of the pts with new HO, 65% (24/37) reported at least one flare-up (mean rate of 2.3 flare-ups/year). Over 12 months, 60% (56/93) of pts did not have new HO; 43% (24/56) of them reported at least one flare-up (mean rate of 1.8 flare-ups/year). Mean changes from Baseline in CAJIS and FOP-PFQ were minimal: CAJIS: 0.6 (SD=2.4; median=1.0; n=99) and FOP-PFQ: 4.4% (SD=11.2; median=3.7%; n=90); and were similar across pts with or without new HO. Conclusions: In participants with FOP, although deterioration of physical function is expected over a patient’s lifetime, CAJIS and FOP-PFQ scores did not worsen significantly in the relative short-term of this study. However, HO volume, quantified by WBCT, increased over the course of 12 months. These results show that measuring HO may be a viable way to monitor changes in FOP over short periods of time.