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This report relates the case histories of two sisters who demonstrated the typical symptoms of progeria at birth. One of these children had died previous to this study. The familial occurrence underlines the thesis that progeria is an autosomal-recessive disorder. The examination of the cultured skin fibroblasts from the younger child showed a clear decrease in cell growth. On the other hand, the immunfluorescent examination of skin biopsies and cultured skin fibroblasts revealed no atypical distribution of collagen types.

Samples of bone from a patient with osteogenesis imperfecta were found to synthesize and contain type III collagen as well as type I collagen. Normal bone contains only type I collagen except in the lining cells of the bone marrow cavities. In the patient's tissue, type III collagen was localized in nonfibrillar structures in discrete areas of the bone. These and previous studies indicate that certain types of osteogenesis imperfecta may be caused by a failure of normal bone maturation and the sites in which the type III collagen is found appear to be defects in the bone.

Synthesis of collagen by chondrocytes was studied by immunofluorescence using antibodies specific for type I, II and III collagen. The following tissues and culture conditions were chosen for this immunohistological study: normal articular cartilage, epiphyseal growth cartilage, cartilage undergoing osteoarthrotic degeneration, suspension culture and monolayer culture. While type II collagen is the unique collagen all over hyaline cartilage, type I collagen is produced by hypertrophic chondrocytes in the growth plate. In addition, chondrocytes in osteoarthrotic areas of articular cartilage synthesize type I collagen. Under in vitro culture conditions, chondrocytes initially produce type II collagen and synthesize later on type I collagen. The change of synthesis from type II to type I collagen is more rapid in monolayer than in suspension culture. It is concluded that the presence of matrix compounds and the cellmatrix interaction as well are necessary to maintain synthesis of type II collagen in chondrocytes. Alterations in the cell-matrix interactions are shown to occur in the hypertrophic zone of the epiphyseal growth plate, in cartilage undergoing osteoarthrotic degeneration as well as in chondrocytes grown in culture. Thus, change in the control of gene activity may subsequently lead to change in collagen synthesis. It is possible that the synthesis of type I collagen, which cannot fulfil the physiological function of a structural element in cartilageneous tissue, is a crucial factor in the process of osteoarthrosis.