Summary
Background Inactivating mutations of the calcium‐sensing receptor (CaSR), a G‐protein‐coupled receptor with extracellular (ECD), transmembrane (TMD) and intracellular (ICD) domains, cause ...familial hypocalciuric hypercalcaemia, neonatal severe primary hyperparathyroidism and occasionally primary hyperparathyroidism in adults.
Objective To investigate a patient with typical symptomatic primary hyperparathyroidism for CaSR abnormalities.
Patient and design A 51‐year‐old woman with primary hyperparathyroidism was investigated for CaSR abnormalities as her severe hypercalcaemia (3·75 mm) persisted after the removal of two large parathyroid adenomas and she was the daughter of normocalcaemic consanguineous parents. Following informed consent, CASR mutational analysis was undertaken using leucocyte DNA. Wild‐type and mutant CaSR constructs were expressed in human embryonic kidney (HEK) 293 cells and assessed by measuring their intracellular calcium responses to changes in extracellular calcium. Clinical data were pooled with previous studies to search for genotype–phenotype correlations.
Results The proband was homozygous for a Pro339Thr CaSR missense mutation, located in the ECD, and her normocalcaemic relatives were heterozygous. The mutant Thr339 CaSR had a rightward shift in its dose–response curve with a significantly higher EC50 = 3·18 mm ± 0·19 compared to the wild‐type EC50 = 2·16 mm ± 0·1 (P < 0·01), consistent with a loss‐of‐function mutation. An analysis of CaSR mutations in patients with primary hyperparathyroidism revealed that those of the ECD were associated with a significantly greater hypercalcaemia that was less likely to be corrected after removal of the parathyroid tumours.
Conclusions A CaSR missense mutation causing a loss‐of‐receptor‐function can cause symptomatic primary hyperparathyroidism in adulthood.
Objectives Hypoparathyroidism is a rare disease in children that occurs as a result of autoimmune destruction of the parathyroid glands, a defect in parathyroid gland development or secondary to ...physical parathyroid gland disturbance. Typical symptoms of hypoparathyroidism present as hypocalcaemia and hyperphosphatemia due to decreased parathyroid hormone secretion and may lead to nerve and muscles disturbances resulting in clinical manifestation of tetany, arrhythmias and epilepsy. Currently, there is no conventional hormone replacement treatment for hypoparathyroidism and therapeutic approaches include normalising mineral levels using an oral calcium supplement and active forms of vitamin D. Case presentation We present the case of a 10-year-old girl with primary hypoparathyroidism who had no prior history of autoimmune disorders, but who subsequently developed systemic lupus erythematosus.
Familial isolated primary hyperparathyroidism (FIHP) is an autosomal dominant disorder that can represent an early stage of either the multiple endocrine neoplasia type 1 (MEN1) or ...hyperparathyroidism-jaw tumor (HPT-JT) syndromes; alternatively, the condition can be caused by an allelic variant of MEN1 or HRPT2 (hyperparathyroidism 2 gene), or caused by a distinct entity involving another locus. We have explored these possibilities in a patient with primary hyperparathyroidism, whose mother had a history of renal calculi and primary hyperparathyroidism.
Serum biochemistry and radiological investigations for primary hyperparathyroidism, MEN1 and HPT-JT, and genetic testing for MEN1 and HRPT2 mutations were undertaken.
FIHP with primary hyperparathyroidism as the sole endocrinopathy due to a previously unreported heterozygous missense germline MEN1 mutation, Tyr351Asn. In addition, another unreported heterozygous missense germline MEN1 mutation, Trp220Leu, was identified in an unrelated male patient with FIHP, whose mother and sister also had primary hyperparathyroidism. DNA from a parathyroid tumor from the sister revealed a loss of heterozygosity in which the mutant allele was retained. This is consistent with Knudson's 'two-hit' model of hereditary cancer and a tumor suppressor role for MEN1 in FIHP.
The patient underwent parathyroidectomy and has remained normocalcemic over a follow-up period of 6 years. The other four patients have remained normocalcemic for a follow-up period of 4-15 years following parathyroidectomy. None has developed abnormalities of the MEN1 syndrome, providing further support that FIHP is a distinct genetic variant of the MEN1 syndrome.
Heterozygous germline gain-of-function mutations of G-protein subunit α11 (Gα11), a signaling partner for the calcium-sensing receptor (CaSR), result in autosomal dominant hypocalcemia type 2 (ADH2). ...ADH2 may cause symptomatic hypocalcemia with low circulating parathyroid hormone (PTH) concentrations. Effective therapies for ADH2 are currently not available, and a mouse model for ADH2 would help in assessment of potential therapies. We hypothesized that a previously reported dark skin mouse mutant (Dsk7) - which has a germline hypermorphic Gα11 mutation, Ile62Val - may be a model for ADH2 and allow evaluation of calcilytics, which are CaSR negative allosteric modulators, as a targeted therapy for this disorder. Mutant Dsk7/+ and Dsk7/Dsk7 mice were shown to have hypocalcemia and reduced plasma PTH concentrations, similar to ADH2 patients. In vitro studies showed the mutant Val62 Gα11 to upregulate CaSR-mediated intracellular calcium and MAPK signaling, consistent with a gain of function. Treatment with NPS-2143, a calcilytic compound, normalized these signaling responses. In vivo, NPS-2143 induced a rapid and marked rise in plasma PTH and calcium concentrations in Dsk7/Dsk7 and Dsk7/+ mice, which became normocalcemic. Thus, these studies have established Dsk7 mice, which harbor a germline gain-of-function Gα11 mutation, as a model for ADH2 and have demonstrated calcilytics as a potential targeted therapy.
LEARNING POINTS To confirm hypocalcaemia, calculate serum albumin-adjusted calcium concentrations; in patients who are critically ill or have acid-base disorders, ionised calcium measurements are ...needed Careful clinical assessment may show common causes of hypocalcaemia, such as post-surgical hypoparathyroidism, chronic kidney disease, or drugs Serum parathyroid hormone measurements are central to investigating and classifying causes of hypocalcaemia; other tests include serum phosphate, magnesium, and creatinine concentrations Serum vitamin D measurements are indicated in patients with inadequate exposure to sunlight, nutritional deficiency, or malabsorption syndrome
Genetics of Skeletal Disorders Hannan, Fadil M; Newey, Paul J; Whyte, Michael P ...
Handbook of experimental pharmacology,
2020, Letnik:
262
Journal Article, Book Chapter
Recenzirano
Odprti dostop
Bone and mineral diseases encompass a variety of conditions that involve altered skeletal homeostasis and are frequently associated with changes in circulating calcium, phosphate, or vitamin D ...metabolites. These disorders often have a genetic etiology and comprise monogenic disorders caused by a single-gene mutation, which may be germline or somatic, or an oligogenic or polygenic condition involving multiple genetic variants. Single-gene mutations causing Mendelian diseases are usually highly penetrant, whereas the gene variants contributing to oligogenic or polygenic disorders are each associated with smaller effects with additional contributions from environmental factors. The detection of monogenic disorders is clinically important and facilitates timely assessment and management of the patient and their affected relatives. The diagnosis of monogenic metabolic bone disorders requires detailed clinical assessment of the wide variety of symptoms and signs associated with these diseases. Thus, clinicians should undertake a systematic approach commencing with careful history taking and physical examination, followed by appropriate laboratory and skeletal imaging investigations. Finally, clinicians should be familiar with the range of molecular genetic tests available to ensure their appropriate use and interpretation. These considerations are reviewed in this chapter.
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