Synopsis of Clinical Aspect and Main Radiographic Features
The first row shows congenital dislocation of the left knee and clubfoot in patient 3, diagnosed with Larsen syndrome, at a few days of age (the appearance is identical to that of the HSD patient reported by Hall 11 ). At birth, the left leg was extended in such a way that the foot rested against the thoracic wall. The central photograph shows marked valgus deformity of the knees and bilateral clubfoot in patient 5 at age 2 yr. The right panels show patient 1, a girl, at age 5 yr, after several surgical procedures had been carried out to stabilize the dislocated knees and the dysplastic hips. Note also the inability to extend the elbows completely. The second row shows the bifid humerus and radial dislocation, as well as the knee dislocation or subluxation with delayed development of the knee epiphyses (patient identification and ages are within the panels). The third row shows the diagnostically useful spinal changes: In the AP projection, there is marked widening of the interpedicular space from T12 to L1 (the arrows mark the vertebral body of L1); the interpedicular space then decreases progressively from L3 to L5. In the lateral projection, notching or scalloping of the upper and lower endplates of the lumbar vertebral bodies can be seen; these changes have been emphasized in the original descriptions of humero-spinal dysostosis 9,10 . The changes are more pronounced in the younger patients.

Disaccharide Composition of Chondroitin Sulfate Synthesized by Fibroblast Cultures
Fibroblasts from two controls and from patients 1 and 2 were labeled simultaneously with the radiolabeled glycosaminoglycan sugar precursor, [6-³H]glucosamine, and the chondroitin sulfate synthesized was harvested, purified, and cleaved into its constituent disaccharides, ΔDi-0S, ΔDi-4S and ΔDi-6S. These were separated by high-performance liquid chromatography (HPLC) and measured (see Supplemental Material and Methods). In patients' cells, the proportion of ΔDi-6S (black bars) is markedly reduced at basal condition; under stimulation of GAG synthesis with beta-D-xylopiranoside, the difference between controls and patients increases further. The bars show the percentage of each of the three disaccharides (and the standard error of the mean) in each experiment. The statistical significance of the difference between the value of each disaccharide in the patient cell lines and the mean of the same disaccharide in the two control lines was calculated with Student's t test; ^∗ p < 0.01; ^∗∗ p < 0.001.

Scheme of the CHST3 Gene and Protein
The upper part is a schematic representation of the CHST3 exon-intron structure and of the coding regions. Immediately below, the small horizontal arrows indicate the position of primer couples used to amplify genomic DNA. The lower part is a schematic representation of the CHST3 protein with its transmembrane domain and the intraluminal sulfotransferase domain as inferred from data on the Expasy site. Above the protein are mutations leading to premature stop codons as well as the putative splicing mutation (see Table 1 and Supplemental Material and Methods, available online); below the proteins are amino acid substitutions, including the R304Q substitution reported by Thiele et al., 2 and the known polymorphism R357Q.