MATN3 and multiple epiphyseal dysplasia: Although considerable progress has been made in understanding the disease mechanisms of MED caused by mutations in COMP [Unger and Hecht, 2001] and SLC26A2 [Forlino et al., 2005; Rossi and Superti-Furga, 2001], virtually nothing is known about the disease mechanisms of MED caused by mutations in MATN3. The aim of this study therefore was to determine the molecular cell pathology of MED caused by MATN3 mutations.