COL2A1 and Tibial pseudarthrosis: Crossing the Col2a1(collagen, type II, alpha 1)-Cre promoter mouse with the Nf1flox/flox mouse, the authors found that the Nf1/Col2−/− mice showed progressive scoliosis, tibial pseudoarthrosis, and skeletal abnormalities involving the skull and anterior chest wall, demonstrating that loss of Nf1 in axial and appendicular osteo-chondro progenitors recapitulates the skeletal abnormalities of NF1 patients [12].