Based on clinical features and molecular mutations, the ten families were classified into five definite COL2A1-related disorders: four families with spondyloepiphyseal dysplasia congenita (SEDC), three with osteoarthritis with mild chondrodysplasia (OSCPD), one with Czech dysplasia, one with Kniest dysplasia, and one with epiphyseal dysplasia, multiple, with myopia and deafness (EDMMD). The gene discussed is COL2A1; the disease is Kniest dysplasia.