Familial hypocalciuric hypercalcaemia (FHH) is clinically characterized by mild to moderate parathyroid hormone (PTH)-dependent hypercalcaemia, autosomal dominant pattern of inheritance, and normal to frankly reduced urinary calcium excretion in spite of a high serum calcium (clearance (Ca)/clearance (Cr)<0.01). FHH has a benign course and should be differentiated from primary hyperparathyroidism. It is usually caused by a heterozygous loss-of-function mutation in the calcium-sensing receptor gene (CASR).
We report the case of a 16-year-old patient with hypercalcaemia and a mixed family history of parathyroid adenoma and mild hypercalcaemia. Serum calcium was 14 mg/dl with a serum iPTH of 253 pg/ml.
A neck 99mTc-sesta MIBI tomoscintigraphy showed a definite hyperactivity in the left upper quadrant. A surgical four-gland exploration confirmed a single parathyroid adenoma. After surgical resection of a left superior parathyroid adenoma, the patient's hypercalcemia improved but did not normalize, returning to a level typical of FHH. An inactivating mutation in exon 4 of the CASR gene, predicting a p.Glu297Lys amino acid substitution was found.
Thus, this 16-year old patient presented with the association of FHH and a single parathyroid adenoma. The young age of the patient and the association of parathyroid adenoma and FHH in his grandmother argue for a causal link between CASR mutation and parathyroid adenoma in this family. This case contributes to illustrate the expanding clinical spectrum of CASR loss-of-function mutations.