Kaplan, Frederick S.

Case: Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder characterized by progressive heterotopic ossification. Scoliosis may develop and progress rapidly, especially during adolescence. We report 4 patients with FOP and scoliosis during early adolescence: A 12-year-old girl underwent T4-S2 posterior spinal fusion (PSF); another 12-year-old girl underwent T4-S2 PSF; a 13-year-old boy underwent T3-L4 PSF; and a 14-year-old girl was managed nonoperatively because the complex deformity and ankylosed shoulders could not be adequately balanced with surgery. Conclusion: In patients with FOP, surgical intervention can reduce thoracic deformity and improve pulmonary function but carries substantial risks, including heterotopic ossification.

Abstract Fibrodysplasia ossificans progressiva (FOP) is an ultra-rare genetic condition characterized by congenital malformations of the great toes and progressive heterotopic ossification (HO) in specific anatomic patterns. Present management summarized here is focused on early diagnosis, assiduous avoidance of injury and iatrogenic harm, symptomatic amelioration of painful flare-ups, and optimization of residual function. Twenty-one members of the International Clinical Council on FOP (ICC) and seven consultants from 15 countries, chosen for their clinical expertise in FOP, developed this summary statement. Further advances in therapeutics will be based on rigorous clinical trials to assess novel and emerging treatment and prevention strategies. A detailed and updated exploration of the topics outlined in this brief perspective can be found in “The Medical Management of Fibrodysplasia Ossificans Progressiva: Current Treatment Considerations” which can be found on the International Clinical Council on FOP (ICC) website (www.iccfop.org).

Abstract Pseudoarthroses (false joints) occur as a complication of fracture healing in the normotopic skeleton but have not been reported at ectopic sites. Fibrodysplasia ossificans progressiva (FOP) is an ultra-rare genetic disorder characterized by progressive heterotopic ossification (HO) and congenital skeletal abnormalities including developmental arthropathy in the normotopic skeleton. Here, we report ectopic pseudojoint formation in 6 patients with FOP, all occurring after painful flare-ups and HO in soft connective tissues of the knee, hip, and forearm. To our knowledge, FOP is the only human condition in which ectopic pseudojoint formation occurs. These findings support that dysregulated BMP pathway signaling from mutant ACVR1 mediates not only HO, but also ectopic pseudojoint formation, and that ectopic pseudojoints can arise from de novo musculoskeletal elements.

» Fibrodysplasia ossificans progressiva (FOP), the most severe form of heterotopic ossification (HO) in humans, may lead to severe thoracic deformity (TD) and thoracic insufficiency syndrome (TIS), the most common cause of mortality in individuals with FOP. » In this study, we examine the multiple causes of TD in FOP and propose a dynamic model for the development and evolution of TD that can be used to guide clinical care. This model posits that multiple factors, all originating from the causative gain-of-function mutation in activin receptor A, type 1, lead to TD in FOP. » Factors that lead to TD in FOP include early developmental costovertebral and facet joint arthropathy and joint ankylosis, progressive episodic flare-ups (both trauma induced or spontaneous) and subsequent HO, dysregulated soft tissue sensitivity to mechanical stimuli, growth plate dysregulation, and congenital rib fusions. These factors contribute to TD in FOP through a combination of intra-articular and extra-articular mechanisms, all amplified by growth. » Although FOP is a rare condition, it is illustrative of how a mutation in a critical receptor in the bone morphogenetic protein signaling pathway can cause a litany of musculoskeletal dysfunction that can lead to life-threatening consequences. Clinicians caring for individuals who have FOP must be aware of the occurrence, evolution, and implications of progressive TD and resultant TIS so that appropriate preventive measures such as avoidance of pulmonary infections, incentive spirometry, and diaphragmatic strengthening can be instituted.

In the introduction to his 1970 textbook BIOCHEMISTRY, Albert Lehninger wrote “Living things are composed of lifeless molecules [...]

Abstract Fibrodysplasia ossificans progressiva (FOP) is an ultra-rare disorder, characterized by progressive heterotopic ossification (HO) and painful soft-tissue inflammatory flare-ups. This was a post hoc analysis from a phase 2 (NCT03188666) trial in which adults with FOP received intravenous anti-activin A antibody garetosmab 10 mg/kg or placebo every 4 wk over 28 wk (Period 1), followed by a 28-wk open-label treatment and extension (Periods 2 and 3). Here we describe flare-ups, their relationship to new HO lesions, and the impact of garetosmab on flare-ups. Volume of new HO lesions was measured by CT. Patient-reported flare-ups were defined by any 2 of the following: new onset of pain, swelling, joint stiffness, decrease in movement, or perceived presence of HO. Flare-ups were experienced by 71% (17/24) of placebo-treated patients, 59% (10/17) of whom developed a new HO lesion irrespective of flare-up location; 24% of flare-ups location-matched new HO lesions. Twenty-nine new HO lesions occurred in the placebo cohort by week 28, of which 12 (41%) occurred in the same location as new or ongoing flare-ups. A higher volume of newly formed heterotopic bone (week 28) occurred in placebo-treated patients who had experienced a prior flare-up vs those without (median [Q1:Q3] of 16.6 [12.0:31.1] vs 3.2 cm3). Garetosmab was previously shown to decrease patient-reported flare-up frequency in Period 1; here, garetosmab reduced the median (Q1:Q3) duration of patient-reported flares (15.0 [6.0:82.0] vs 48.0 [15.0:1.00] d) and the severity of flare-ups vs placebo. Frequency of corticosteroid use was numerically reduced in those treated with garetosmab (40.0%) vs placebo (58.3%). In this analysis, 71% of placebo-treated adults with FOP experienced flare-ups over 28 wk, which were associated with an increased volume of newly formed heterotopic bone. Garetosmab reduced the severity and duration of flare-ups, with effects sustained during the entire trial.

The formation of bone outside the normal skeleton, or heterotopic ossification (HO), occurs through genetic and acquired mechanisms. Fibrodysplasia ossificans progressiva (FOP), the most devastating genetic condition of HO, is due to mutations in the ACVR1/ALK2 gene and is relentlessly progressive. Acquired HO is mostly precipitated by injury or orthopedic surgical procedures but can also be associated with certain conditions related to aging. Cellular senescence is a hallmark of aging and thought to be a tumor-suppressive mechanism with characteristic features such as irreversible growth arrest, apoptosis resistance, and an inflammatory senescence-associated secretory phenotype (SASP). Here, we review possible roles for cellular senescence in HO and how targeting senescent cells may provide new therapeutic approaches to both FOP and acquired forms of HO.