COL2A1 and chondrodysplasia: Besides, P.7 carries pathogenic variants in both COL2A1 and COL9A2 mutations resulting in a more severe skeletal deformity and short-trunk dwarfism, while the other two patients (P.16, P.17) in our study only carrying COL9A1/COL9A2 mutation had very mild symptoms, with only mild chondrodysplasia.