PRRX1 and osteogenesis imperfecta type 5: To study whether the human OI type V phenotype is recapitulated in this model, we crossed mice that were heterozygous for the Rosa26-knockin mIfitm5 allele (Rosa26mIfitm5/+) with: (a) paired related homeobox 1 (Prx1-Cre) transgenic mice that expressed the Cre recombinase (Cre/–) in mesenchymal precursor cells of the osteo-chondroprogenitor lineage, and (b) osteocalcin-Cre (OC-Cre) transgenic mice that expressed the Cre-recombinase (Cre/–) in mature osteoblasts.