UNDERSULFATION OF PROTEOGLYCANS SYNTHESIZED BY CHONDROCYTES FROM A PATIENT WITH ACHONDROGENESIS TYPE 1B HOMOZYGOUS FOR AN L483P SUBSTITUTION IN THE DIASTROPHIC DYSPLASIA SULFATE TRANSPORTER

Achondrogenesis type 1B is an autosomal recessive, lethal chondrodyspl asia caused by mutations in the gene encoding a sulfate/chloride antip orter of the cell membrane (Superti-Furga, A., Hastbacka, J., Wilcox, W. R., Cohn, D. H., van der Harten, J. J., Rossi, A., Blau, N., Rimoin , D. L., Steinmann, B., Lander, E. S., and Gitzelmann, R. (1996) Not. Genet. 12, 100-102). To ascertain the consequences of the sulfate tran sport defect on proteoglycan synthesis, we studied the structure and s ulfation of proteoglycans in cartilage tissue and in fibroblast and ch ondrocyte cultures from a fetus with achondrogenesis 1B. Proteoglycans extracted from epiphyseal cartilage and separated on agarose gels mig rated more slowly than controls and stained poorly with alcian blue. T he patient's cultured cells showed reduced incorporation of [S-35]sulf ate relative to [H-3]glucosamine, impaired uptake of sulfate, and high er resistance to chromate toxicity compared to control cells. Epiphyse al chondrocytes cultured in alginate beads synthesized proteoglycans o f normal molecular size as judged by gel filtration chromatography, bu t undersulfated as judged by ion exchange chromatography and by the am ount of nonsulfated disaccharide. High performance liquid chromatograp hy analysis of chondroitinase-digested proteoglycans showed that sulfa ted disaccharides were present, although in reduced amounts, indicatin g that at least in vitro, other sources of sulfate can partially compe nsate for sulfate deficiency. A t1475c transition causing a L483P subs titution in the eleventh transmembrane domain of the sulfate/chloride antiporter was present on both alleles in the patient who was the prod uct of a consanguineous marriage. The results indicate that the defect of sulfate transport is expressed in both chondrocytes and fibroblast s and results in the synthesis of proteoglycans bearing glycosaminogly can chains which are poorly sulfated but of normal length.