UNDERSULFATION OF CARTILAGE PROTEOGLYCANS EX-VIVO AND INCREASED CONTRIBUTION OF AMINO-ACID SULFUR TO SULFATION IN-VITRO IN MCALISTER-DYSPLASIA ATELOSTEOGENESIS TYPE-2

Mutations in the diastrophic dysplasia sulfate transporter gene cause a family of chondrodysplasias including, in order of increasing severi ty, diastrophic dysplasia, atelosteogenesis type 2 and achondrogenesis type 1B, McAlister dysplasia is a lethal chondrodysplasia considered on the basis of minor radiographic features to be a disorder different from atelosteogenesis type 2, Here, we demonstrate that McAlister dys plasia arises from mutations in the diastrophic dysplasia sulfate tran sporter gene and that this disorder essentially coincides on molecular and biochemical grounds with atelosteogenesis type 2. The fetus affec ted by McAlister dysplasia we have studied is a compound heterozygote for mutations leading to R279W and N425D substitutions in the diastrop hic dysplasia sulfate transporter. Proteoglycan sulfation was studied in epiphyseal cartilage and in chondrocyte cultures of the patient by high performance liquid chromatography of chondrotinase digested prote oglycans; a high amount of non-sulfated disaccharide was observed as a consequence of the alteration of the transporter function caused by t he mutations, However, sulfated disaccharides were detectable even if in low amounts, both in cultured cells and tissue. Functional impairme nt of the sulfate transporter was demonstrated in vitro by reduced inc orporation of [S-35]sulfate relative to [H-3]glucosamine in proteoglyc ans synthesized by chondrocytes and by sulfate-uptake assays in fibrob lasts. Parallel in vitro studies in a patient with achondrogenesis 1B indicated that the severity of the clinical phenotype seems to be corr elated to the residual activity of the sulfate transporter. The capaci ty of fibroblasts to use cysteine as an alternative source of sulfate was evaluated by double-labeling experiments. Relative incorporation o f [S-35]cysteine-derived sulfate in the glycosaminoglycan chains was i ncreased in the patient's cells, indicating that, in vitro, the catabo lism of sulfur-containing amino acids can partially compensate for int racellular sulfate deficiency. Residual sulfation observed in proteogl ycans extracted from cartilage suggests that this mechanism may be ope rating also ill vivo.