Case Reports of Patients Diagnosed with Familial Hypocalciuric Hypercalcemia, A Disorder That Should be Kept in Mind in Hypercalcemia Cases

Familial hypocalciuric hypercalcemia (FHH) causes hypercalcemia by three genetic mechanisms: Inactivating mutations in the calcium-sensing receptor (CaSR), G-protein subunit α11 or adapter-associated protein complex 2, sigma 1 subunit. In other cases, hypercalcemia causes significant morbidity and mortality, while FHH usually follows a benign course. Failure to diagnose FHH may result in unwarranted treatment or surgery for a false diagnosis of primary hyperparathyroidism, given the significant overlap of biochemical features. Patients carrying a heterozygous loss-of-function mutation in the CaSR gene are typically referred to as FHH-type 1 (FHH1). Although FHH1 causes lifelong hypercalcemia, it is usually benign and asymptomatic. FHH is the most common syndrome of CaSR gene mutation; it may sometimes be associated with a hypercalciuric tendency depending on the variant. Although hypercalcemia is a frequently encountered condition in our clinical practice, FHH is a clinic that we do not often think of. This paper presents a family diagnosed with FHH, having heterozygous CaSR mutations in three generations.