PROLIFERATION AND COLLAGEN BIOSYNTHESIS OF OSTEOBLASTS AND CHONDROCYTES IN SHORT RIB SYNDROME TYPE BEEMER

We report on a case of lethal short-limbed skeletal dysplasia with extremely short ribs, median cleft upper lip and palate, malrotation of intestine, lung hypoplasia with bilateral segmentation defect, atrial septum defect, union of distal urethra and vagina, and complex brain malformations. Based on radiological criteria and the pattern of associated abnormalities a short rib syndrome without polydactyly (Type Beemer) was diagnosed. Morphologically, the growth plate showed a reduced proliferation zone and an enlarged zone of hypertrophic cartilage. In addition, islands of persistent hypertrophic cartilage were present even in the metaphysis. In monolayer cell cultures supplemented with 10% fetal calf serum proliferation was normal in articular chondrocytes, reduced in costal chondrocytes, and elevated in osteoblasts from the patient. Clonal growth of costal and articular chondrocytes in methylcellulose could be stimulated normally by insulin-like growth factor-I (IGF-I), IGF-II, and human growth hormone (hGH). However, the response to transforming growth factor beta1 (TGF-beta1) was markedly elevated in articular chondrocytes of the patient compared to those of 3 fetal controls. Quantitative collagen synthesis in both osteoblasts and chondrocytes from the patient did not differ significantly from that of controls. Osteoblasts synthesized predominantly collagen I and minor amounts of collagen III, chondrocytes synthesized primarily collagen II. All collagen chains including CNBr-peptides of collagen II showed normal migration in PAA gel electrophoresis.