RESUMEN
Fibrodysplasia ossificans progressiva (FOP) or myositis ossificans, is a genetic disease, with a prevalence of 1 in 2.000.000. It is caused by pathogenic variants in ACVR1 gene and characterized by soft tissue heterotopic ossification, starting in the second decade of life. It is associated to early mortality caused by respiratory complications. It evolves in flare-ups, triggered by soft tissue injuries; therapy is symptomatic, using analgesia, steroids and diphosphonates. We report a 12-year-old female with left renal agenesis, hallux valgus and intellectual disability, presenting with a six months history of thoracic kyphosis, tender nodules in the thorax, and rigidity of right elbow and left knee. Clinical examination revealed dysmorphic facial features. A magnetic resonance showed heterotopic ossification nodules, which was confirmed with spinal radiography. These findings prompted the diagnosis of FOP. Pain treatment was started, and prednisone was used during flare-ups. The ACVR1 gene was analyzed and a pathogenic variant, p. Arg206His, was found, confirming the diagnosis of FOP.