Phenotype of Parathyroid-targeted Cdc73 Deletion in Mice Is Strain-dependent.

Hyperparathyroidism jaw-tumor syndrome is an autosomal dominant disorder caused by mutations in the CDC73/HRPT2 tumor suppressor gene, encoding parafibromin, and manifesting benign or malignant parathyroid tumors, ossifying jaw fibromas, uterine tumors, and kidney lesions. Sporadic parathyroid carcinomas also frequently exhibit inactivating CDC73 mutations and loss of parafibromin. To study the role of CDC73 in parathyroid cell proliferation in vivo, we generated mice with a parathyroid-specific deletion of Cdc73. Homozygous knockout mice on a mixed B6/129/CD1 background had decreased serum calcium and PTH and smaller parathyroid glands compared with heterozygous or wild-type littermates, whereas homozygous Cdc73-null mice on other backgrounds exhibited no abnormalities in parathyroid gland function or development. No hypercalcemia or parathyroid hypercellularity was observed in mice of any background examined at any age. Thus, although postnatally acquired complete loss of CDC73 causes parathyroid cell proliferation and hyperparathyroidism, such as seen in human hyperparathyroidism jaw-tumor syndrome, our results suggest that earlier, developmentally imposed complete loss of Cdc73 can cause a primary defect in parathyroid gland structure/function in a strain-dependent manner. This striking disparity in parathyroid phenotype related to genetic background offers a unique opportunity in an in vivo model system to precisely dissect and identify the responsible molecular mechanisms.