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Walker V. The Intricacies of Renal Phosphate Reabsorption-An Overview. Int J Mol Sci 2024; 25:4684. [PMID: 38731904 PMCID: PMC11083860 DOI: 10.3390/ijms25094684] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2024] [Revised: 04/17/2024] [Accepted: 04/19/2024] [Indexed: 05/13/2024] Open
Abstract
To maintain an optimal body content of phosphorus throughout postnatal life, variable phosphate absorption from food must be finely matched with urinary excretion. This amazing feat is accomplished through synchronised phosphate transport by myriads of ciliated cells lining the renal proximal tubules. These respond in real time to changes in phosphate and composition of the renal filtrate and to hormonal instructions. How they do this has stimulated decades of research. New analytical techniques, coupled with incredible advances in computer technology, have opened new avenues for investigation at a sub-cellular level. There has been a surge of research into different aspects of the process. These have verified long-held beliefs and are also dramatically extending our vision of the intense, integrated, intracellular activity which mediates phosphate absorption. Already, some have indicated new approaches for pharmacological intervention to regulate phosphate in common conditions, including chronic renal failure and osteoporosis, as well as rare inherited biochemical disorders. It is a rapidly evolving field. The aim here is to provide an overview of our current knowledge, to show where it is leading, and where there are uncertainties. Hopefully, this will raise questions and stimulate new ideas for further research.
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Affiliation(s)
- Valerie Walker
- Department of Clinical Biochemistry, University Hospital Southampton NHS Foundation Trust, Southampton General Hospital, Southampton S016 6YD, UK
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2
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Abstract
Recent data suggest an increase in the overall incidence of parathyroid disorders, with primary hyperparathyroidism (PHPT) being the most prevalent parathyroid disorder. PHPT is associated with morbidities (fractures, kidney stones, chronic kidney disease) and increased risk of death. The symptoms of PHPT can be nonspecific, potentially delaying the diagnosis. Approximately 15% of patients with PHPT have an underlying heritable form of PHPT that may be associated with extraparathyroidal manifestations, requiring active surveillance for these manifestations as seen in multiple endocrine neoplasia type 1 and 2A. Genetic testing for heritable forms should be offered to patients with multiglandular disease, recurrent PHPT, young onset PHPT (age ≤40 years), and those with a family history of parathyroid tumors. However, the underlying genetic cause for the majority of patients with heritable forms of PHPT remains unknown. Distinction between sporadic and heritable forms of PHPT is useful in surgical planning for parathyroidectomy and has implications for the family. The genes currently known to be associated with heritable forms of PHPT account for approximately half of sporadic parathyroid tumors. But the genetic cause in approximately half of the sporadic parathyroid tumors remains unknown. Furthermore, there is no systemic therapy for parathyroid carcinoma, a rare but potentially fatal cause of PHPT. Improved understanding of the molecular characteristics of parathyroid tumors will allow us to identify biomarkers for diagnosis and novel targets for therapy.
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Affiliation(s)
- Smita Jha
- Metabolic Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-1752, USA
| | - William F Simonds
- Metabolic Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-1752, USA
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Khadse S, Takalikar VS, Ghildiyal R, Shah N. Rare cause of persistent hypocalcaemia in infancy due to PTH gene mutation. BMJ Case Rep 2023; 16:e256358. [PMID: 37699739 PMCID: PMC10503314 DOI: 10.1136/bcr-2023-256358] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/14/2023] Open
Abstract
Hypocalcaemia is a frequently encountered electrolyte abnormality in neonates and it is mostly transient. However, persistent hypocalcaemia can point towards an endocrine abnormality like hypoparathyroidism, which is usually due to genetic disorders like DiGeorge and Kearns Sayre syndrome or due to mutations of genes like GCM2, CaSR and PTH.Our patient was a female child, who presented with hypocalcaemic convulsions in the neonatal period. On laboratory assessment, serum phosphate levels were noted to be high along with inappropriately low parathyroid hormone (PTH) levels. The child was diagnosed to have hypoparathyroidism and was started on oral calcium and 1,25-dihydroxycholecalciferol supplements to which she responded well. However, the child was lost to follow-up and was readmitted with hypocalcaemic convulsions in infancy. Clinical exome analysis done was diagnostic of homozygous PTH gene mutation. This case demonstrates a rare form of congenital isolated hypoparathyroidism with no other syndromic associations.
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Affiliation(s)
- Savita Khadse
- Pediatrics, Lokmanya Tilak Municipal General Hospital and Lokmanya Tilak Municipal Medical College, Mumbai, Maharashtra, India
| | - Vrushali Satish Takalikar
- Pediatrics, Lokmanya Tilak Municipal General Hospital and Lokmanya Tilak Municipal Medical College, Mumbai, Maharashtra, India
| | - Radha Ghildiyal
- Pediatrics, Lokmanya Tilak Municipal General Hospital and Lokmanya Tilak Municipal Medical College, Mumbai, Maharashtra, India
| | - Nikhil Shah
- Pediatrics, Lokmanya Tilak Municipal General Hospital and Lokmanya Tilak Municipal Medical College, Mumbai, Maharashtra, India
- Division of Pediatric Endocrinology, Department of Pediatrics, Surya Children's Hospital, Chembur, Mumbai, Maharashtra, India
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Hanna P, Khatri A, Choi S, Brabant S, Gild ML, Piketty ML, Francou B, Prié D, Potts JT Jr, Clifton-Bligh RJ, Linglart A, Gardella TJ, Jüppner H. Homozygous Ser-1 to Pro-1 mutation in parathyroid hormone identified in hypocalcemic patients results in secretion of a biologically inactive pro-hormone. Proc Natl Acad Sci U S A 2023; 120:e2208047120. [PMID: 36795755 DOI: 10.1073/pnas.2208047120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023] Open
Abstract
Like other secreted peptides, nascent parathyroid hormone (PTH) is synthesized with a pre- and a pro-sequence (25 and 6 amino acids, respectively). These precursor segments are sequentially removed in parathyroid cells before packaging into secretory granules. Three patients from two unrelated families who presented during infancy with symptomatic hypocalcemia were found to have a homozygous serine (S) to proline (P) change affecting the first amino acid of the mature PTH. Unexpectedly, biological activity of synthetic [P1]PTH(1-34) was indistinguishable from that of unmodified [S1]PTH(1-34). However, in contrast to conditioned medium from COS-7 cells expressing prepro[S1]PTH(1-84), medium from cells expressing prepro[P1]PTH(1-84) failed to stimulate cAMP production despite similar PTH levels when measured by an intact assay that detects PTH(1-84) and large amino-terminally truncated fragments thereof. Analysis of the secreted, but inactive PTH variant led to the identification of pro[P1]PTH(-6 to +84). Synthetic pro[P1]PTH(-6 to +34) and pro[S1]PTH(-6 to +34) had much less bioactivity than the corresponding PTH(1-34) analogs. Unlike pro[S1]PTH(-6 to +34), pro[P1]PTH(-6 to +34) was resistant to cleavage by furin suggesting that the amino acid variant impairs preproPTH processing. Consistent with this conclusion, plasma of patients with the homozygous P1 mutation had elevated proPTH levels, as determined with an in-house assay specific for pro[P1]PTH(-6 to +84). In fact, a large fraction of PTH detected by the commercial intact assay represented the secreted pro[P1]PTH. In contrast, two commercial biointact assays that use antibodies directed against the first few amino acid residues of PTH(1-84) for capture or detection failed to detect pro[P1]PTH.
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Newey PJ, Hannan FM, Wilson A, Thakker RV. Genetics of monogenic disorders of calcium and bone metabolism. Clin Endocrinol (Oxf) 2022; 97:483-501. [PMID: 34935164 PMCID: PMC7614875 DOI: 10.1111/cen.14644] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 10/24/2021] [Accepted: 11/07/2021] [Indexed: 12/19/2022]
Abstract
Disorders of calcium homeostasis are the most frequent metabolic bone and mineral disease encountered by endocrinologists. These disorders usually manifest as primary hyperparathyroidism (PHPT) or hypoparathyroidism (HP), which have a monogenic aetiology in 5%-10% of cases, and may occur as an isolated endocrinopathy, or as part of a complex syndrome. The recognition and diagnosis of these disorders is important to facilitate the most appropriate management of the patient, with regard to both the calcium-related phenotype and any associated clinical features, and also to allow the identification of other family members who may be at risk of disease. Genetic testing forms an important tool in the investigation of PHPT and HP patients and is usually reserved for those deemed to be an increased risk of a monogenic disorder. However, identifying those suitable for testing requires a thorough clinical evaluation of the patient, as well as an understanding of the diversity of relevant phenotypes and their genetic basis. This review aims to provide an overview of the genetic basis of monogenic metabolic bone and mineral disorders, primarily focusing on those associated with abnormal calcium homeostasis, and aims to provide a practical guide to the implementation of genetic testing in the clinic.
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Affiliation(s)
- Paul J Newey
- Division of Molecular and Clinical Medicine, Ninewells Hospital & Medical School, University of Dundee, Scotland, UK
| | - Fadil M Hannan
- Nuffield Department of Women's and Reproductive Health, University of Oxford, Oxford, UK
| | - Abbie Wilson
- Division of Molecular and Clinical Medicine, Ninewells Hospital & Medical School, University of Dundee, Scotland, UK
| | - Rajesh V Thakker
- Academic Endocrine Unit, Oxford Centre for Diabetes, Endocrinology & Metabolism (OCDEM), Churchill Hospital, University of Oxford, Oxford, UK
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Lee JH, Lee S. The parathyroid glands and parathyroid hormone: Insights from PTH gene mutations. Vitam Horm 2022; 120:79-108. [PMID: 35953118 DOI: 10.1016/bs.vh.2022.04.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Nine mutations have been discovered in the parathyroid hormone (PTH) gene since it was initially sequenced in 1983. An autosomal dominant C18R mutation in the signal peptide was first reported in 1990, followed by an exon skipping mutation, leading to loss of exon 2 in 1992; the latter mutation prevents PTH biosynthesis, as exon 2 contains the initiation codon. The S23P and S23X mutations affecting the same residue were reported in 1999 and 2012, respectively, while in 2008, the somatic mutation, R83X, was detected in a parathyroid adenoma tissue sample from a patient with overt hyperparathyroidism. In 2013, the heterozygous p.Met1_Asp6del mutation was discovered incidentally in a case-control study, while another heterozygous mutation, M14K, was detected in the signal peptide 4 years later. In 2015, a homozygous R56C mutation was reported, and was the first hypoparathyroidism-causing mutation identified that affects the mature bioactive portion of PTH; this mutation has significantly contributed to the understanding of the molecular mechanisms involved in signal transduction through the PTH receptor. Recently, a novel homozygous S32P mutation was identified, which is also situated in the bioactive portion of PTH. The discovery of these nine mutations in the PTH gene and determination of the molecular mechanisms underlying their effects has provided deep insights into the synthesis, processing, and secretion of PTH. Future attempts to discover other such mutations will help elucidate as yet unknown functions of PTH, with potential clinical implications.
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Affiliation(s)
- Joon-Hyop Lee
- Laboratory of Genomics and Translational Medicine, Gachon University College of Medicine, Incheon, Korea; Department of Surgery, Gachon University College of Medicine, Incheon, Korea
| | - Sihoon Lee
- Laboratory of Genomics and Translational Medicine, Gachon University College of Medicine, Incheon, Korea; Department of Internal Medicine, Gachon University College of Medicine, Incheon, Korea.
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Andersen SL, Frederiksen AL, Rasmussen AB, Madsen M, Christensen AMR. Homozygous missense variant of PTH (c.166C>T, p.(Arg56Cys)) as the cause of familial isolated hypoparathyroidism in a three-year-old child. J Pediatr Endocrinol Metab 2022; 35:691-694. [PMID: 35120289 DOI: 10.1515/jpem-2021-0752] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/14/2021] [Accepted: 01/17/2022] [Indexed: 11/15/2022]
Abstract
OBJECTIVES Hypoparathyroidism is a rare disorder which is predominantly of idiopathic or genetic origin in children. The diagnosis is made from the biochemical measurement of parathyroid hormone (PTH), and the key findings include a low PTH in combination with hypocalcemia and hyperphosphatemia. However, the level of PTH encountered in patients with hypoparathyroidism may be dependent on the underlying genetic cause of the disorder as well as the biochemical assay used for assessment of PTH. CASE PRESENTATION A three-year-old child with asymptomatic primary hypoparathyroidism was identified with a homozygous missense variant of PTH. A sudden unexpected high PTH result after a shift from 2nd to 3rd generation PTH assay in the routine laboratory provided a clue on the underlying genetic etiology. CONCLUSIONS Pathogenic variants of PTH as a cause of hypoparathyroidism are rarely described. In this case, the child was asymptomatic, and discordant PTH results were seen with different assays.
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Affiliation(s)
- Stine Linding Andersen
- Department of Clinical Biochemistry, Aalborg University Hospital , Aalborg, Denmark.,Department of Clinical Medicine, Aalborg University , Aalborg, Denmark
| | - Anja Lisbeth Frederiksen
- Department of Clinical Medicine, Aalborg University , Aalborg, Denmark.,Department of Clinical Genetics, Aalborg University Hospital , Aalborg, Denmark
| | | | - Mette Madsen
- Department of Pediatrics, Aalborg University Hospital , Aalborg, Denmark.,Steno Diabetes Center North Jutland, Aalborg University Hospital , Aalborg, Denmark
| | - Ann-Margrethe Rønholt Christensen
- Department of Pediatrics, Aalborg University Hospital , Aalborg, Denmark.,Steno Diabetes Center North Jutland, Aalborg University Hospital , Aalborg, Denmark
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Hawkes CP, Al Jubeh JM, Li D, Tucker SE, Rajiyah T, Levine MA. Novel PTH Gene Mutations Causing Isolated Hypoparathyroidism. J Clin Endocrinol Metab 2022; 107:e2449-e2458. [PMID: 35165722 PMCID: PMC9113798 DOI: 10.1210/clinem/dgac086] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/15/2022] [Indexed: 11/19/2022]
Abstract
CONTEXT Parathyroid hormone (PTH) gene mutations represent a rare cause of familial isolated hypoparathyroidism (FIH). These defects can cause hypoparathyroidism with increased or decreased serum levels of PTH through 1) impaired PTH synthesis; 2) induction of parathyroid cell apoptosis; or 3) secretion of bioinactive PTH molecules. Eight pathogenic mutations of this gene have been described previously. OBJECTIVE Through describing 2 novel mutations of the PTH gene, we aim to extend the molecular basis for FIH and further refine the proposed mechanisms by which PTH mutations cause hypoparathyroidism. METHODS Proband case reports were compiled with extended family analysis. The probands in both kindreds presented before age 10 days with hypocalcemia and elevated phosphate levels. Proband A had low PTH levels, whereas these levels were elevated in Proband B. Proband B was initially diagnosed with pseudohypoparathyroidism. Methylation analysis was performed of CpG dinucleotides within 3 GNAS differentially methylated regions; whole-genome sequencing; and PTH infusion with analysis of nephrogenous 3',5'-cyclic adenosine 5'-monophosphate. RESULTS Proband A had a novel heterozygous sequence change in exon 2 of the PTH gene, c.46_47delinsAA (p.Ala16Lys), and proband B had a novel homozygous nucleotide transition in PTH exon 3 (c.128G > A; p.G43E) that led to replacement of glycine by glutamic acid at position 12 of PTH 1-84. PTH 1-34 infusion demonstrated that renal responsiveness to PTH was intact and not antagonized by circulating bioinactive PTH. CONCLUSION PTH gene mutations are uncommon causes of hypoparathyroidism, but can be misdiagnosed as disorders of gland development or receptor function if PTH levels are decreased or elevated, respectively. Genetic testing should be considered early in the diagnostic approach to these presentations.
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Affiliation(s)
- Colin P Hawkes
- Division of Endocrinology and Diabetes, The Children’s Hospital of Philadelphia (CHOP), Philadelphia, Pennsylvania, USA
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
- Department of Paediatrics and Child Health, University College Cork, Cork, Ireland
| | - Jamal M Al Jubeh
- Department of Pediatrics, Sheikh Khalifa Medical City, Abu Dhabi, United Arab Emirates
| | - Dong Li
- Center for Applied Genomics, CHOP, Philadelphia, Pennsylvania, USA
| | - Susan E Tucker
- Section of Adult and Pediatric Endocrinology, Diabetes, and Metabolism, The University of Chicago, Chicago, Illinois, USA
| | - Tara Rajiyah
- Section of Adult and Pediatric Endocrinology, Diabetes, and Metabolism, The University of Chicago, Chicago, Illinois, USA
| | - Michael A Levine
- Division of Endocrinology and Diabetes, The Children’s Hospital of Philadelphia (CHOP), Philadelphia, Pennsylvania, USA
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
- Correspondence: Michael A. Levine, MD, Division of Pediatric Endocrinology and Diabetes, The Children’s Hospital of Philadelphia, ARC510A, 3615 Civic Center Blvd, Philadelphia, PA 19104, USA.
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Abstract
Parathyroid hormone (PTH) and PTH-related peptide (PTHrP) regulate extracellular phosphate and calcium homeostasis as well as bone remodeling. PTH is a classic endocrine peptide hormone whose synthesis and negative feedback by multiple factors control release from the parathyroid glands. PTHrP is ubiquitously expressed (pre- and postnatally) and acts in an autocrine/paracrine manner. This review considers the structural pharmacology and actions of PTH and PTHrP, biological consequences of inherited mutations, engineered analogs that illuminate similarities and differences in physiologic actions, and targeted therapeutic opportunities.
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Affiliation(s)
- Larry J Suva
- Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine and Biomedical Sciences, Texas Veterinary Medical Center 4466 Texas A&M University, College Station, TX, United States
| | - Peter A Friedman
- Department of Pharmacology and Chemical Biology, Laboratory for GPCR Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States.
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