Unusually long-term survival in a feline with Fibrodysplasia ossificans progressiva (FOP-like) disease without

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder characterized by heterotopic ossification within the connective tissues that affects the muscles, tendons, and joint capsules. It is an autosomal inherited condition caused by mutations in ACVR1, which is associated with ectopic bone formation. A 5-year-old neutered male outdoor cat, clinically diagnosed with FOP-like disease three years prior, presented for follow-up evaluation owing to an unusually long survival. New blood samples and radiographs were obtained to assess disease progression and investigate the patient's genetic background, with the aim of describing this case's clinical evolution and new genetic findings, and sharing the patient's exceptionally rare long-term survival with peers. Radiographic evaluation revealed severe progression of osteoarticular disease, partial to total resorption of previously deposited mineralized tissue, marked hypertrophy of the limb musculature, and an overall increase in radiographic muscular density. Genetic analysis confirmed the absence of the ACVR1 mutation. This is the first reported case of FOP-like disease in a cat in Uruguay, with no ACVR1 mutation detected and an unusually long survival of more than three years after diagnosis.