Decreased expression of calcium-sensing receptor and parafibromin in secondary hyperparathyroidism with an abnormal whole PTH/intact PTH ratio.

A 34-year-old female hemodialysis patient with an abnormal whole parathyroid hormone (PTH)/intact PTH ratio (ratio = 1.14) underwent parathyroidectomy for advanced secondary hyperparathyroidism. The abnormal PTH ratio indicated a relative increase in the serum N-terminus PTH, a new molecular form of PTH. The abnormal ratio normalized immediately after the largest parathyroid gland (PTG) was removed, proving the largest PTG as causative. An immunohistochemical analysis revealed extremely decreased expression of the calcium-sensing receptor and parafibromin in the largest PTG in comparison with the other PTGs. This case indicated the possible involvement of decreased calcium-sensing receptor and parafibromin signaling in the development of the abnormal PTH ratio.