Any multiple epiphyseal dysplasia in which the cause of the disease is a mutation in the COL9A1 gene. The disease is epiphyseal dysplasia, multiple, 6 (MONDO_0013591). Also known as: COL9A1 multiple epiphyseal dysplasia (disease), epiphyseal dysplasia, multiple, type 6, multiple epiphyseal dysplasia (disease) caused by mutation in COL9A1.