We therefore used IHC and SDS–PAGE western blotting to study three additional mouse models of ER stress-induced chondrodysplasia; mild PSACH resulting from a mutation in the C-terminal globular domain of COMP (Comp T585M) (11), severe PSACH resulting from a common in-frame deletion in the type III repeat of COMP (Comp D469del) (13) and MCDS resulting from a NC1 mutation in type X collagen (Col10a1 N617 K) (14). This evidence concerns the gene COL18A1 and chondrodysplasia.