Heterozygous inactivating mutations in the
calcium-sensing receptor (CaSR) gene are known to cause
familial hypocalciuric hypercalcemia (FHH), usually a benign form of
hypercalcemia without symptoms of a disrupted
calcium homeostasis. FHH can be mistaken for the more common
primary hyperparathyroidism (PHPT), for which surgical treatment may be needed. We describe a case of a 36-year-old woman with
hypercalcemia and elevated PTH, initially suspected of having PHPT. Sequencing of the CaSR-gene revealed a mutation in
nucleotide 437, changing the
amino acid in position 146 from
Glycine to
Aspartate. The mutation was previously undescribed in the literature, but a very low
calcium:
creatinine clearance ratio supported the diagnosis FHH. A few years later, the patient's two daughters were tested and the association between mutation and
hypercalcemia could be confirmed. The patient was
gastric bypass-operated and therefore, due to malabsorption and increased risk of fracture, was in need of adequate
calcium supplementation. The chronically elevated
calcium levels challenged medical followup, as
calcium sufficiency could not be monitored in a traditional manner. Eventually the patient developed elevated
alkaline phosphatase, a further increased PTH and a decreased DXA T-score indicating
calcium deficiency and
bone resorption. As a supplement, all CaSR-mutations found at our hospital, 2005-2018.