COL2A1 and Schmid metaphyseal chondrodysplasia: We crossed our collagen X p.Asn617Lys knock-in mouse model of MCDS (ColXN617K) [11] with mice in which Col2a1-Cre/loxP-mediated deletion of Xbp1 exon 2 renders Xbp1 completely inactive specifically in chondrocytes (Xbp1CartΔEx2) [14], to generate ColXN617K/Xbp1CartΔEx2 (C/X).