(A) xylosyltransferase activity from normal, early OA and late-stage OA cartilage of three representative patients. Data are mean ± SD of 3 experiments per parameter, per joint, per patient. **Significantly (P<0.01) higher than all groups; *significantly (P<0.01) higher than normal and late groups; §significantly (P<0.05) lower than normal. (B) GAG chain composition in human cartilage explants as determined by FACE. Proteinase K-digested cartilage explants containing equal amounts (5 µg) of GAGs, as determined by uronic acid assay from each group, were digested with chondroitinase ABC and the disaccharides obtained were fluorotagged and derivatized. Disaccharides were run on a monocomposition gel and gels are representative images from 3 experiments per parameter, per joint, per patient. Markers are ΔDi0S, nonsulfated chondroitin-unsaturated disaccharide; ΔDi4S, chondroitin-4-sulfated unsaturated disaccharide; ΔDi6S, chondroitin-6-sulfated unsaturated disaccharide.