Thus, we crossed our collagen X p.Asn617Lys knock-in mouse model of MCDS (ColXN617K) [11] with our Xbp1CartΔEx2 mouse, in which XBP1 activity is ablated specifically from chondrocytes [14], to generate the compound mutant, ColXN617K/Xbp1CartΔEx2 (C/X). The gene discussed is XBP1; the disease is Schmid metaphyseal chondrodysplasia.