Previously, we described that the founder P937R mutation in the ZNF687 gene causes a severe form of PDB complicated by giant cell tumor degeneration (GCT/PDB).14,20,35 To determine the effect of the P937R mutation on bone metabolism and PDB pathogenesis, we generated the Zfp687 knock-in mouse model. The gene discussed is ZNF687; the disease is granular cell tumor.