SOX9 and scoliosis: In contrast, alterations of bulk ECM components, including COLII and GAG proteoglycans, were not significantly affected at the onset of scoliosis, suggesting that even minor alterations in SOX9 expression in the postnatal IVD of mice may be sufficient to initiate biomechanical instability leading to disc wedging and driving the onset of spine curvature, without grossly affecting tissue architecture and composition of the major ECM components of the IVD.