COL9A1 and multiple epiphyseal dysplasia: Multiple epiphyseal dysplasias are caused by variants in the genes encoding important cartilage extracellular matrix proteins, enzymes, and transporter proteins, including COMP, MATN3, COL9A1, COL9A2, COL9A3, CANT1, and SLC26A2. We aimed to investigate the clinical, radiographic, and molecular findings, along with the natural course of the disease, in a group of patients with multiple epiphyseal dysplasia.