In an earlier era, osteitis fibrosa cystica (OFC), the specific bone lesion due to excess parathyroid hormone (PTH) secretion was an important diagnostic clue to the presence of primary hyperparathyroidism (PHPT) and was almost always associated with large parathyroid adenomas and vitamin D and calcium deficiency (6–9). This evidence concerns the gene PTH and osteitis fibrosa.