CASR and parathyroid hyperplasia: In addition, 15% to 20% have multiple parathyroid gland hyperplasias or adenomas (5), which are often associated with abnormalities in calcium regulatory sites due to mutations in calcium-sensing receptor (CaSR) signaling pathway genes (CASR, GNA11, AP2S1), and environmental factors, such as a history of cervical radiation or prolonged lithium treatment, can contribute to the development of the disease by interfering with the function of the CaSR (2).