SOX9 and Tracheomalacia: A reduction of ECM gene expressions observed in the SOX9 HT model explained the underdeveloped and deformed cartilage tissues, such as tracheomalacia and clubfoot, in CD patients. While there is no literature reporting the relationship between SOX9 and chromosome segregation, research has shown that SOX9 upregulates chondrocyte proliferation rate [23], which may imply that SOX9 promotes cell proliferation by upregulating chromosome segregation processes.