COL10A1 and Schmid metaphyseal chondrodysplasia: Misfolded mutant protein retention and pathological ER stress causing the UPR has been identified as a common disease mechanism in several forms of skeletal dysplasia including MED and metaphyseal chondrodysplasia type Schmid caused by mutations in the gene encoding type X collagen (COL10A1) (MCDS, OMIM # 156500) [3,8].