Ultrastructure of dermal connective tissue in fibrodysplasia ossificians progressiva

The ultrastructure of dermal connective tissue in two patients suffering from fibrodysplasia ossificans progressiva (syn myositis o.p.) was studied. The disorder starts with soft tissue swelling which subsequently ossify. The connective tissue of various organs may be affected. No defects in calcium metabolism have been discovered. It was intended to study the primary event which initiates the ossification. The present ultrastructural study demonstrates an accumulation of proteoglycan microfibrils as well as glycoprotein material in dermal connective tissue. Both substances are prerequisites of calcification resulting from the binding of calcium and phosphorus ions. A subsequent release of proteolytic enzymes in the tissues may be set free the bound iones and, thus, initiate mineralization.