Familial hypocalciuric hypercalcemia is an autosomal dominant genetic disorder characterized by mild to moderate hypercalcemia, mild hypermagnesemia, and normal or inappropriately elevated parathyroid hormone levels. Familial hypocalciuric hypercalcemia 1 is the most prevalent form of familial hypocalciuric hypercalcemia and is typically caused by heterozygous loss-of-function mutations in the calcium-sensing receptor (CaSR) gene. Homozygous CaSR mutations are more commonly associated with neonatal severe primary hyperparathyroidism. We report the case of a female patient in her early 40s harboring a novel homozygous frameshift mutation in the CaSR gene (c.2603_2604insTT), resulting in familial hypocalciuric hypercalcemia 1. The patient presented with persistent hypocalciuria, hypercalcemia, and primary hyperparathyroidism, along with a family history of consanguinity. This case highlights the phenotypic variability associated with CaSR mutations and broadens the clinical spectrum of homozygous CaSR-related disorders. Increased clinical awareness of atypical genetic presentations is essential to avoid misdiagnosis and to ensure appropriate management of patients with familial disorders of calcium homeostasis.

Primary hyperparathyroidism is a constitutive excess of parathyroid hormone (PTH) in the blood, caused by an idiopathic defect of growth and/or function of the parathyroid glands. PHPT is usually an acquired disease, due to the sporadic development of parathyroid hyperplasia, adenoma, and, in extremely rare cases, malignant carcinoma, mainly occurring by the sixth decade of life. In about 5-10 % of cases PHPT manifests in the context of congenital disorders, having a genetic base and occurring much earlier in life, compared to the sporadic counterpart. Congenital PHPT can manifest as isolated PHPT or as syndromic PHPT in the context of complex multiorgan disorders. Non-syndromic inherited PHPT includes Familial Hypocalciuric Hypercalcemia types 1, 2 and 3, Neonatal Severe Primary Hyperparathyroidism, and three different genetic forms of Familial Isolated Hyperparathyroidism, while syndromic inherited PHPT includes Hyperparathyroidism-Jaw Tumor Syndrome and Multiple Endocrine Neoplasias types 1, 2 A and 4.

The calcium-sensing receptor (CaSR) gene encodes a cell membrane G protein-coupled receptor (GPCR) which has a key role in maintaining the extracellular Ca2+ homeostasis. We aimed at correcting the compound heterozygous mutation in the 6th [c.1656delA, p.I554SfsX73] and 7th [c.2217 T > A, p.C739X] exons of the CASR gene which the original patient-derived iPSC line had. The mutation is associated with neonatal severe primary hyperparathyroidism of the patient. We generated and characterized a CRISP/Cas9-edited hiPSC line with the restored sequence in the sixth exon of the CASR gene, bearing only heterozygous mutation in the 7th exon. The results showed that the new genetically modified cell line has karyotype without abnormalities, typical hiPSCs morphology, characteristic expression of pluripotency markers, and ability to develop into three germ layers, and differentiates in chondrogenic, adipogenic, osteogenic directions. This new cell line will complement the existing pool of CaSR-mutated cell lines, a valuable resource for in-depth understanding of neonatal severe primary hyperparathyroidism. This will allow further exploration of the application of pharmacological drugs in the context of personalized medicine to correct Ca-homeostasis disorders.

Familial primary hyperparathyroidism (PHPT) includes syndromic and non-syndromic disorders. The former are characterized by the occurrence of PHPT in association with extra-parathyroid manifestations and includes multiple endocrine neoplasia (MEN) types 1, 2, and 4 syndromes, and hyperparathyroidism-jaw tumor (HPT-JT). The latter consists of familial hypocalciuric hypercalcemia (FHH) types 1, 2 and 3, neonatal severe primary hyperparathyroidism (NSHPT), and familial isolated primary hyperparathyroidism (FIHP). The familial forms of PHPT show different levels of PHPT penetrance, developing earlier and with multiglandular involvement compared to sporadic counterpart. All these diseases exhibit Mendelian inheritance patterns, and for most of them, the genes responsible have been identified. DNA testing for predisposing mutations is helpful in index cases or in individuals with a high suspicion of the disease. Early recognition of hereditary disorders of PHPT is of great importance for the best clinical and surgical approach. Genetic testing is useful in routine clinical practice because it will also involve appropriate screening for extra-parathyroidal manifestations related to the syndrome as well as the identification of asymptomatic carriers of the mutation. The aim of the review is to discuss the current knowledge on the clinical and genetic profile of these disorders along with the importance of genetic testing in clinical practice.

Familial hypocalciuric hypercalcemia (FHH) is one of the conditions that should be considered in the differential diagnosis of hypercalcemia and normo-hypophosphatemia in childhood. Heterozygous Calcium-sensing receptor (CASR) gene mutations cause FHH, and homozygous CASR gene mutations cause neonatal severe primary hyperparathyroidism (NSHPT). Cinacalcet is an allosteric modulator of Calciumsensing receptor (CaSR), and has been used in the treatment of these clinical entities in recent years. A 26-month-old boy was examined for a recurrent rash. During the evaluation, hypercalcemia (13.3 mg/ dL), hypophosphatemia (2.3 mg/dL) and inappropriately normal PTH level (67 pg/mL) were observed. Neck and renal ultrasonography were normal. The parathyroid scintigraphy was unremarkable. The patient`s family members were also evaluated, and hypocalciuria (fractional excretion of calcium were 0.01%, 0.04% on two separate tests) was detected concurrently with the patient`s hypercalcemia. The mother`s serum calcium was 10.2 mg/dL, the father`s was 10.6 mg/dL, and the brother`s was 12.8 mg/dL. CASR gene sequencing showed a novel homozygous mutation in exon 4 (c.1057G > A), which had generated a substitution of the amino acid glutamate to lysine at codon 353 (p.Glu353Lys). This mutation was homozygous in the children and heterozygous in the parents. Fluid hydration, furosemide, oral phosphorus, prednisolone, pamidronate and cinacalcet treatments were used in the management of hypercalcemia of the proband. A longer and more effective control was achieved with cinacalcet treatment. FHH can be seen in heterozygous as well as homozygous CASR gene mutations. Different clinical findings may occur in different individuals from the same family. Cinacalcet therapy can be used successfully in the treatment of individuals with FHH.