Wei Z, Li S, Tao X, et al. - Since Paget's disease of bone (PDB) is a late‐onset chronic progressive bone disease characterized by abnormal activation of osteoclasts that results in bone pain, deformities, and fractures, researchers examined an extended Chinese pedigree with 8 individuals affected by early‐onset and polyostotic PDB, two of whom developed giant cell tumors (GCTs). The results show mutations in PFN1 as the pathological mechanism in PDB/GCT, and Pfn1‐mutated mice have been successfully identified as an effective animal model for studying PDB‐associated pathological mechanisms. In detecting PDB individuals predisposed to developing GCTs, the detection of PFN1 mutations has great diagnostic importance.