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.

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