“…The rapid, excessive, focal new bone deposition in PD results in woven bone that is much weaker, can bow and cause bone deformity, fracture, skull thickening, bone pain, secondary osteoarthritis, and nerve root compression (2). The primary cellular abnormality in PD resides in the osteoclast (OCL) (3). OCLs are increased in number and size and express a pagetic phenotype that distinguishes them from normal OCLs (4), including hypermultinucleation, increased TAF12 levels (a coactivator of VDRmediated transcription), and increased 1,25-(OH) 2 D 3 and RANKL responsivity (5)(6)(7).…”