Among these, known associated genes were TBX4 and NOTCH2. We further found very damaging mutations in three collagen genes: COL12A1, COL2A1, and COL9A1. Mutations in COL2A1 are known to cause spondyloepiphyseal dysplasia and COL2A1 has previously been related to osteoarthritis secondary to DDH (Granchi et al. 2002). Here, TBX4 is linked to spondyloepiphyseal dysplasia.