Objective: The coexistence of familial hypocalciuric hypercalcemia (FHH) and primary hyperparathyroidism (PHPT) is extremely rare. Genetic evidence has demonstrated a causal relationship between FHH and the presence of inactivating mutations in the calcium-sensing receptor gene.
Method: We herein report a 60-year-old German patient who was referred for hypercalcemia and increased PTH levels found incidentally during normal routine blood tests.
Results: The patient underwent surgical exploration and the diagnosis of PHPT was histologically confirmed. One week later, the follow-up blood tests revealed recurrent hypercalcemia, and the possibility of FHH was reconsidered. Genetic analysis was performed and revealed a novel heterozygous CaSR single missense mutation (Arg551Gly) within the extracellular CaSR domain.
Conclusion: We report a novel heterozygous missense inactivating mutation within the extracellular CaSR domain in a German subject with FHH and histologically proven PHPT.