[A series of clinical cases of familial hypocalciuric hypercalcemia syndrome].

Familial hypocalciuric hypercalcemia (FHH) - rare disease with predominantly autosomal dominant inheritance. FHH typically develops due to a heterozygous inactivating mutation in the calcium-sensitive receptor gene (CASR), less commonly due to heterozygous mutations in GNA11 and AP2S1. CASR mutations lead to an increase in the threshold for calcium sensitivity, which requires a higher concentration in serum to reduce the release of PTH. These changes are accompanied by an increase of calcium and magnesium reabsorption in the proximal tubules, which leads to hypercalcemia and hypocalciuria. Basically, FHH may be asymptomatic or accompanied by mild hypercalcemia. FHH doesn't require surgical treatment, unlike primary hyperparathyroidism (PHPT), therefore, differential diagnosis of these two conditions is extremely important. In addition, immediate relatives of a proband with FHH also require the exclusion of disease inheritance. We analyzed a series of clinical cases with a genetically confirmed diagnosis of FHH. Our clinical cases indicate a variety of clinical manifestations and the difficulties of differential diagnosis with PHPT.