FIBRODYSPLASIA OSSIFICANS PROGRESSIVA (FOP) is a rare heritable disorder of connective tissue characterized by congenital malformations of the great toes and by progressive heterotopic endochondral osteogenesis in predictable anatomic and temporal patterns. Disease flare-ups can occur spontaneously or can be induced by minor trauma such as intramuscular injections. FOP is the most extensive disorder of heterotopic osteogenesis in humans and leads to catastrophic disability by early adulthood. Bone morphogenetic protein-4, a potent bone inducing morphogen, is overexpressed in lymphocytes of patients with FOP. At the present time, there is no effective treatment or prevention.The pictures illustrate characteristic features of FOP in early childhood. The presence of short malformed great toes at birth (A, arrows) heralds the later spontaneous appearance of the pre-osseous soft-tissue lesion on the neck and back (B, arrow heads) and should provoke suspicion of FOP even before the transformation to heterotopic bone (arrows). An inspection of the toes (C) will confirm the diagnosis and may alleviate the need for a lesional biopsy (trauma) that could exacerbate the condition.
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