COMP and skeletal dysplasia: In several mouse models, a disrupted ER homeostasis in chondrocytes was shown to lead to the accumulation of poorly folded or misfolded proteins with a similar radiological phenotype and it was suggested that ER stress itself results to the skeletal dysplasia.12 In a COMP mutation mouse model it was described that ER stress results in a disturbed articular cartilage structure.13 All these disturbed features are expected to have the most profound effect on the epiphyseal growth plate and the costo-chondral junction and might explain the observed histological abnormalities in our case.