Fibrodysplasia ossificans progressiva and synovial chondromatosis.

Two cases of an unusual association-fibrodysplasia ossificans progressiva and synovial chondromatosis-in non-related children are presented. This association does not seem coincidental and raises several questions about the pathogenesis. A genetic hypothesis related to G proteins is proposed. This is supported by the fact that such abnormalities have been demonstrated in pseudohypoparathyroidism and fibrous dysplasia; these diseases can also be associated with fibrodysplasia ossificans progressiva.