Interestingly, Case 1’s younger sister was found to have a PCC and testing of germline from this patient demonstrated the CHEK2 c.1100delC mutation, but no mutation in PCC susceptibility genes, such as RET, TMEM127, MAX, VHL, SDHA, SDHB, SDHC, SDHD, and NF1. Case 2 did not have any other endocrine tumors such as hyperparathyroidism or medullary thyroid cancer consistent with MEN2 syndrome, or other PCC-related syndromes. The gene discussed is CHEK2; the disease is hyperparathyroidism.