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Parathyroid hormone

Parathyroid hormone (PTH) is an 84-amino-acid peptide hormone secreted primarily by the chief cells of the four parathyroid glands, which are small endocrine glands located posterior to the thyroid gland in the neck.^[1] It serves as the central regulator of calcium and phosphate homeostasis in the human body, responding to fluctuations in blood calcium levels to maintain essential physiological balance.^[2] Produced as a precursor protein (pre-pro-PTH) that is cleaved into its active form, PTH has a short serum half-life of approximately 2 to 5 minutes and is rapidly cleared by the liver and kidneys.^[1] The primary function of PTH is to elevate serum calcium concentrations when they fall below normal levels, thereby supporting critical processes such as nerve transmission, muscle contraction, and cardiac function.^[3] In bone, PTH stimulates osteoclast activity indirectly through osteoblasts, promoting the resorption of calcium and phosphate from the skeletal matrix into the bloodstream.^[1] At the kidneys, it enhances calcium reabsorption in the distal tubules while inhibiting phosphate reabsorption in the proximal tubules, and it activates the enzyme 1-alpha-hydroxylase to convert inactive vitamin D into its active form (calcitriol), which in turn boosts intestinal calcium absorption.^[2] These coordinated actions ensure that blood calcium remains within a narrow range of about 8.5 to 10.5 mg/dL, preventing hypocalcemia-related symptoms like tetany or hypercalcemia-induced complications.^[3] Regulation of PTH secretion occurs via a classic negative feedback loop driven by serum calcium levels, detected by calcium-sensing receptors on parathyroid chief cells; hypocalcemia triggers rapid PTH release, while hypercalcemia suppresses it.^[1] Additional modulators include low serum phosphate, which can stimulate PTH, and elevated calcitriol levels, which inhibit its secretion.^[2] Normal circulating PTH levels, measured as intact PTH, typically range from 15 to 65 picograms per milliliter (pg/mL), though this can vary slightly by laboratory standards.^[2] Dysregulation of PTH, as seen in primary hyperparathyroidism (excess PTH from glandular hyperplasia or adenoma) or hypoparathyroidism (deficient PTH, often post-surgical), can lead to significant metabolic disorders affecting bone health, kidney function, and overall mineral balance.^[3]

Biosynthesis and Structure

Gene Expression and Precursor Processing

The PTH gene, located on the short arm of human chromosome 11 at position 11p15.2-p15.3, consists of three exons and encodes the 115-amino-acid precursor preproparathyroid hormone (preproPTH).^[4] Transcription of the PTH gene occurs primarily in the chief cells of the parathyroid glands, producing an mRNA that is translated on ribosomes associated with the rough endoplasmic reticulum (RER).^[5] As preproPTH enters the ER lumen during translation, its N-terminal 25-amino-acid signal (pre) sequence is cleaved by signal peptidase, yielding the 90-amino-acid proPTH.^[1] ProPTH is then transported through the Golgi apparatus to the trans-Golgi network and immature secretory granules, where it undergoes further proteolytic processing by the proprotein convertase furin at paired basic residues (positions 5-6 relative to the mature hormone), generating the mature 84-amino-acid PTH (PTH 1-84).49165-4/fulltext) Unlike many other peptide hormones, parathyroid cells do not express proprotein convertases 1/3 (PC1/3) or 2 (PC2), confirming furin's role as the primary enzyme for this step.^[6] Mature PTH is concentrated and stored in secretory granules within parathyroid chief cells, where it constitutes the majority of stored hormone ready for release.85260-0/fulltext) Release occurs through calcium-regulated exocytosis of these granules, triggered by hypocalcemia via activation of the cell-surface calcium-sensing receptor (CaSR), which couples to G proteins to promote granule fusion with the plasma membrane.^[7] PTH gene expression is tightly regulated at the transcriptional level by extracellular calcium and vitamin D. The CaSR suppresses PTH mRNA levels in response to elevated calcium concentrations, acting through mechanisms involving the PTH mRNA 3'-untranslated region to reduce stability and translation.^[8] Similarly, the active vitamin D metabolite 1,25-dihydroxyvitamin D (1,25(OH)₂D) inhibits PTH gene transcription by binding to vitamin D response elements in the promoter region, often in synergy with CaSR-mediated effects to prevent parathyroid hyperplasia.46681-5/fulltext)

Mature Hormone Structure

The mature parathyroid hormone (PTH) is a single-chain polypeptide hormone comprising 84 amino acids, with a molecular weight of approximately 9,500 Da. It is synthesized as a linear peptide lacking cysteine residues and thus devoid of disulfide bonds, relying instead on ionic interactions and hydrogen bonding for stability. The primary structure is characterized by an N-terminal domain (residues 1–34) essential for receptor activation and signaling, a central flexible linker region, and a C-terminal domain (residues 35–84) that modulates binding interactions.^[9]^[10] In solution, the secondary structure of the biologically active N-terminal portion features two amphipathic α-helices: the first spanning residues 4–13 (primarily Glu⁴ to Lys¹³) and the second from residues 21–34 (Phe²¹ to Ala³⁴), as determined by NMR spectroscopy. These helices are connected by a type I β-turn around residues 14–20, conferring flexibility to the molecule. The C-terminal region beyond residue 34 is largely unstructured, with minimal helical content, allowing it to adopt extended conformations during receptor engagement. The tertiary structure emphasizes the amphipathic nature of the N-terminal helices, where hydrophobic faces facilitate membrane association and receptor docking, while hydrophilic surfaces interact with solvent and receptor residues.^[11]^[12] The N-terminal domain of PTH primarily drives activation of the PTH type 1 receptor (PTH1R) by inserting into the transmembrane helix bundle to initiate G-protein signaling, whereas the C-terminal domain binds to the receptor's extracellular domain, enhancing overall affinity and specificity. This bipartite binding mode ensures efficient signal transduction. PTH undergoes rapid metabolic degradation, predominantly via hepatic uptake and renal filtration, resulting in a short plasma half-life of 2–4 minutes for the intact hormone.^[13]^[14]^[1]

Regulation of Secretion

Stimulators

The primary stimulator of parathyroid hormone (PTH) secretion is hypocalcemia, which activates the calcium-sensing receptor (CaSR) on the surface of parathyroid chief cells.^[15] This activation leads to increased intracellular calcium concentration through G-protein-coupled signaling pathways, including phospholipase C activation and inositol trisphosphate-mediated release from intracellular stores, ultimately promoting the exocytosis of stored PTH vesicles.^[16] The CaSR thus serves as the key sensor for extracellular calcium levels, ensuring rapid PTH release to restore normocalcemia within seconds to minutes.^[17] Hyperphosphatemia also directly stimulates PTH secretion through mechanisms independent of calcium levels, primarily by inhibiting the CaSR on parathyroid cells.^[18] Elevated phosphate concentrations reduce CaSR activity, mimicking a state of relative hypocalcemia and thereby enhancing PTH release; this effect is mediated via direct interaction with the receptor's extracellular domain.^[19] In chronic kidney disease, persistent hyperphosphatemia further amplifies this stimulation, contributing to secondary hyperparathyroidism by promoting both secretion and parathyroid gland hyperplasia.^[20] Other factors that promote PTH secretion include low levels of 1,25-dihydroxyvitamin D, which normally suppresses PTH synthesis and release; thus, deficiency leads to reduced feedback inhibition and elevated PTH output.^[21] Beta-adrenergic stimulation, via agonists like isoproterenol acting on β-adrenergic receptors on parathyroid cells, increases cyclic AMP levels and enhances PTH secretion, independent of calcium sensing.^[22] Hypomagnesemia similarly stimulates PTH release in acute settings by impairing CaSR function and reducing intracellular magnesium-dependent suppression of secretion.^[23] The dynamics of PTH secretion differ between acute and chronic stimulation: acute hypocalcemia or other triggers elicit rapid, transient increases in PTH release from preformed stores without altering gland size, whereas chronic stimuli, such as sustained hyperphosphatemia or vitamin D deficiency, promote both prolonged secretion and parathyroid cell proliferation, leading to higher baseline PTH levels.^[20] This adaptation ensures long-term maintenance of mineral homeostasis but can contribute to pathological states if unchecked.^[24]

Inhibitors

The primary physiological inhibitor of parathyroid hormone (PTH) secretion is hypercalcemia, which activates the calcium-sensing receptor (CaSR) on parathyroid chief cells. This activation triggers intracellular signaling pathways, including inhibition of adenylate cyclase, reduced cyclic AMP (cAMP) levels, and decreased PTH exocytosis from secretory vesicles, while also promoting the degradation of intracellular PTH stores.^[25] The relationship follows a steep inverse sigmoidal curve, ensuring rapid suppression to prevent excessive calcium elevation.^[25] 1,25-Dihydroxyvitamin D (calcitriol), the active form of vitamin D, provides tonic inhibition of PTH secretion through direct genomic effects mediated by the vitamin D receptor (VDR) in parathyroid cells. Binding of calcitriol to VDR forms a heterodimer with the retinoid X receptor, which interacts with vitamin D response elements in the promoter region of the PTH gene, suppressing its transcription and reducing PTH synthesis.^[25] This mechanism helps maintain calcium balance by counteracting PTH's own stimulation of calcitriol production in the kidney.^[25] Other factors contributing to PTH suppression include elevated serum magnesium and fibroblast growth factor 23 (FGF23). High magnesium concentrations mimic calcium by activating CaSR, thereby inhibiting PTH release and synthesis, though severe hypomagnesemia can paradoxically impair this regulation.^[25] FGF23, primarily secreted by osteocytes in response to elevated phosphate, binds to fibroblast growth factor receptors complexed with Klotho on parathyroid cells, directly suppressing PTH gene expression and secretion to coordinate phosphate homeostasis.^[25] These inhibitory mechanisms integrate into broader feedback loops involving renal and skeletal responses. For instance, PTH-induced renal calcium reabsorption and bone resorption elevate serum calcium, which then suppresses further PTH release via CaSR; similarly, PTH-stimulated calcitriol synthesis in the kidney enhances intestinal calcium absorption but ultimately feeds back to inhibit PTH transcription through VDR. FGF23 further links bone phosphate release to parathyroid suppression, preventing hyperphosphatemia from exacerbating PTH dysregulation.^[25]

Physiological Functions

Calcium Homeostasis

Parathyroid hormone (PTH) plays a central role in maintaining serum calcium levels within a narrow physiological range by acting on multiple target organs, primarily the bone and kidney, to elevate and stabilize ionized calcium concentrations. This ensures the availability of calcium for essential functions such as muscle contraction, nerve transmission, and blood coagulation. PTH secretion is triggered by low serum calcium, leading to rapid adjustments that prevent hypocalcemia.^[26] In bone, PTH stimulates osteoclast activity indirectly through osteoblasts, which express the PTH receptor and upregulate receptor activator of nuclear factor kappa-B ligand (RANKL), promoting osteoclast differentiation and bone resorption to release calcium into the bloodstream. The net skeletal effect of PTH varies with exposure pattern: intermittent PTH administration, as occurs physiologically with pulsatile secretion, favors anabolic actions by enhancing osteoblast activity and bone formation, whereas continuous elevation leads to predominant catabolic resorption. This dual regulation allows PTH to mobilize calcium stores efficiently without excessive bone loss under normal conditions.^[27]^[28]^[29] In the kidney, PTH enhances calcium reabsorption primarily in the distal convoluted tubule by activating transient receptor potential vanilloid 5 (TRPV5) channels on the apical membrane of tubular epithelial cells via the protein kinase A (PKA) pathway, thereby reducing urinary calcium excretion and conserving systemic levels. This action occurs downstream of adenylyl cyclase activation following PTH binding to its receptor, increasing intracellular cAMP and facilitating calcium entry into cells for basolateral transport. Overall, renal mechanisms contribute significantly to PTH-mediated calcium retention, accounting for up to 20% of filtered calcium under stimulated conditions.^[30]^[31]^[26] PTH maintains the parathyroid set-point for ionized calcium at approximately 1.1-1.3 mmol/L, a tightly regulated threshold where small deviations trigger proportional changes in PTH secretion to restore equilibrium. This set-point reflects the sensitivity of parathyroid chief cells to extracellular calcium via the calcium-sensing receptor, ensuring long-term homeostasis.^[32]^[33] PTH integrates with calcitonin, secreted by thyroid C-cells in response to hypercalcemia, to fine-tune calcium levels; while PTH raises serum calcium, calcitonin opposes this by inhibiting osteoclast activity and promoting renal calcium excretion, providing a counter-regulatory balance. Additionally, PTH indirectly supports intestinal calcium absorption by stimulating renal production of 1,25-dihydroxyvitamin D, though this is a secondary mechanism.^[26]^[34]

Phosphate Homeostasis

Parathyroid hormone (PTH) plays a critical role in maintaining phosphate homeostasis by primarily lowering serum phosphate levels to prevent hyperphosphatemia, achieving this through coordinated actions on the kidney and bone, as well as interactions with other regulatory hormones.^[35] In the kidney, PTH inhibits phosphate reabsorption in the proximal tubule, promoting phosphaturia and thereby reducing serum phosphate concentration. This effect is mediated by the downregulation and internalization of sodium-phosphate cotransporters, particularly NaPi-IIa (also known as SLC34A1), on the apical membrane of proximal tubular cells, which decreases the reabsorption of approximately 80% of filtered phosphate.^[35]^[36] In bone, PTH indirectly contributes to phosphate regulation by stimulating osteoclastic resorption, which releases phosphate into the circulation alongside calcium; however, this potential increase in serum phosphate is counterbalanced by the dominant renal phosphaturic effects of PTH.^[35] While the primary intent of bone resorption is to elevate serum calcium, the associated phosphate mobilization underscores PTH's integrated control over mineral ion balance.^[35] PTH interacts with fibroblast growth factor 23 (FGF23), a bone-derived hormone produced mainly by osteocytes, to ensure coordinated phosphate control; PTH stimulates FGF23 production in bone, which in turn enhances renal phosphate excretion by similarly suppressing NaPi-IIa and provides negative feedback by inhibiting PTH secretion.^[35]^[36] This bone-kidney axis fine-tunes phosphate homeostasis, maintaining normal adult serum phosphate levels within the range of 0.8–1.45 mmol/L.^[37]

Vitamin D Metabolism

Parathyroid hormone (PTH) plays a central role in vitamin D metabolism by stimulating the renal production of the active form of vitamin D, calcitriol (1,25-dihydroxyvitamin D). In the proximal tubules of the kidney, PTH binds to its G-protein-coupled receptor, activating adenylate cyclase and increasing intracellular cyclic AMP (cAMP) levels, which in turn activates protein kinase A (PKA). This signaling pathway upregulates the expression of the enzyme 1-alpha-hydroxylase, also known as CYP27B1, which catalyzes the conversion of 25-hydroxyvitamin D to calcitriol.^[38]^[39] The renal CYP27B1 is the primary site for this hydroxylation step under physiological conditions, ensuring that calcitriol production is tightly regulated in response to PTH levels.^[40] Through the induction of calcitriol synthesis, PTH indirectly enhances intestinal absorption of calcium and phosphate. Calcitriol acts on enterocytes to upregulate the expression of the transient receptor potential vanilloid 6 (TRPV6) channel on the apical membrane, facilitating active transcellular calcium uptake from the intestinal lumen. Similarly, calcitriol increases the expression of the sodium-phosphate cotransporter NaPi-IIb in the brush border membrane, promoting phosphate absorption into enterocytes and subsequent transfer to the bloodstream. These effects amplify mineral bioavailability, supporting overall calcium and phosphate homeostasis without direct PTH action on the intestine.^[41]^[42] Calcitriol exerts negative feedback on PTH and its own production to maintain balance. In the parathyroid glands, calcitriol upregulates the calcium-sensing receptor (CaSR), enhancing sensitivity to extracellular calcium and thereby suppressing PTH secretion. Additionally, calcitriol directly inhibits CYP27B1 expression in the kidney while inducing the catabolic enzyme CYP24A1, which promotes the degradation of both calcitriol and its precursor. This feedback loop prevents excessive vitamin D activation and hypercalcemia.^[43]^[44]^[45]

Clinical Significance

Disorders

Hyperparathyroidism refers to a group of disorders characterized by excessive parathyroid hormone (PTH) secretion, leading to disruptions in calcium and phosphate homeostasis. This excess PTH promotes bone resorption, increases renal calcium reabsorption, and enhances intestinal calcium absorption via vitamin D activation, resulting in hypercalcemia and potential skeletal and renal complications.^[46] Primary hyperparathyroidism arises from autonomous overproduction of PTH by the parathyroid glands, independent of serum calcium levels. The most common cause is a single parathyroid adenoma, accounting for approximately 80-85% of cases, followed by multiglandular hyperplasia in about 15%, with rare instances of multiple adenomas or parathyroid carcinoma. Pathophysiologically, these abnormalities lead to unregulated PTH secretion, causing hypercalcemia, which manifests in symptoms such as kidney stones (nephrolithiasis) in up to 55% of patients, bone loss including osteoporosis and fractures due to increased osteoclast activity, and gastrointestinal issues like constipation. Neuropsychiatric symptoms, including fatigue, depression, and cognitive impairment, may also occur, particularly in severe hypercalcemia.^[46]^[47] Secondary hyperparathyroidism develops as a compensatory response to chronic stimuli that lower serum calcium or raise phosphate levels, prompting parathyroid hyperplasia and elevated PTH. Primary causes include chronic kidney disease (CKD), which impairs phosphate excretion and vitamin D activation, leading to hyperphosphatemia and hypocalcemia in 20-50% of affected individuals, particularly in advanced stages, and vitamin D deficiency, prevalent in about 50% of the global population. The pathophysiology involves persistent stimulation of parathyroid glands, resulting in excessive PTH that initially corrects hypocalcemia but eventually causes bone pain, deformities, fractures from abnormal remodeling, pruritus, muscle weakness, and extraosseous calcifications that can lead to cardiovascular complications.^[48]^[49] Tertiary hyperparathyroidism occurs when prolonged secondary hyperparathyroidism results in autonomous parathyroid function, often after renal transplantation corrects the underlying hypocalcemia but the hyperplastic glands continue overproducing PTH. It affects up to 30% of kidney transplant recipients and is characterized by nodular chief cell hyperplasia involving all four glands in most cases. Symptoms mirror those of primary hyperparathyroidism, including bone pain, fractures, kidney stones, pruritus, pancreatitis, and soft tissue calcifications, though many patients remain asymptomatic until detected by laboratory findings.^[50] Hypoparathyroidism is defined by deficient PTH secretion or action, leading to hypocalcemia and hyperphosphatemia due to impaired calcium mobilization from bone, reduced renal calcium reabsorption, and decreased intestinal absorption. The most frequent cause is iatrogenic, from surgical damage or removal of parathyroid glands during thyroidectomy or other neck procedures. Autoimmune destruction, as in type 1 polyglandular autoimmune syndrome, and genetic conditions like DiGeorge syndrome, which involves thymic and parathyroid hypoplasia, also contribute. Symptoms primarily stem from hypocalcemia and include neuromuscular irritability manifesting as tetany, muscle cramps, paresthesias, seizures, and twitching; chronic cases may develop cataracts, basal ganglia calcifications, and neuropsychiatric issues such as anxiety or depression.^[51] Pseudohypoparathyroidism represents a group of disorders featuring end-organ resistance to PTH, resulting in hypocalcemia and hyperphosphatemia despite normal or elevated PTH levels. It is primarily caused by inactivating mutations in the GNAS gene, which encodes the alpha subunit of the stimulatory G protein essential for PTH signaling; over 400 such mutations have been identified, particularly in pseudohypoparathyroidism type 1a (PHP1a). Pathophysiologically, these mutations impair cAMP production in response to PTH, leading to renal resistance and, in PHP1a, multi-hormone resistance including to thyroid-stimulating hormone. Symptoms include hypocalcemia-related manifestations like paresthesias, muscle spasms, and tetany, alongside features of Albright hereditary osteodystrophy in PHP1a, such as short stature, obesity, round face, and brachydactyly.^[52] Recent recognition has highlighted normocalcemic hyperparathyroidism as a distinct variant of primary hyperparathyroidism, defined by persistently elevated PTH levels with normal serum calcium, after exclusion of secondary causes like vitamin D deficiency or renal impairment. Guidelines from the Fifth International Workshop on the Management of Asymptomatic Primary Hyperparathyroidism (2022) emphasize repeated PTH measurements over at least three months for diagnosis, with prevalence estimates ranging from 0.1% to 6% in screened populations. Patients often present with symptoms such as nephrolithiasis (4-50%) or osteoporosis (0-57%), suggesting a similar pathophysiology of mild autonomous PTH excess but without overt hypercalcemia.^[53]

Measurement and Reference Ranges

The measurement of parathyroid hormone (PTH) primarily involves second-generation immunoassays, such as immunoradiometric assays (IRMA) or chemiluminescent immunoassays, which detect the intact PTH molecule (amino acids 1-84) along with N-terminal truncated fragments like PTH(7-84).^[54]^[55] These assays use two antibodies: one targeting the N-terminal region (typically amino acids 1-34) and another the C-terminal region (amino acids 39-84), allowing for sandwich capture of the full-length hormone and certain fragments that accumulate in conditions like renal impairment.^[56] Third-generation assays, also known as whole or bio-intact PTH assays, employ an additional antibody to specifically target the C-terminal end (amino acid 84), excluding detection of fragments such as PTH(7-84) and providing higher specificity for the biologically active 1-84 form.^[54]^[57] Reference ranges for intact PTH in healthy adults with normal renal function are typically 15-65 pg/mL (1.6-6.9 pmol/L), though these can vary by 20-30% depending on the specific assay platform, population demographics, and laboratory standards.^[2]^[58] Levels tend to increase with age, particularly after 60 years, and are influenced by renal function, where accumulation of inactive fragments in chronic kidney disease (CKD) can elevate apparent PTH values in second-generation assays.^[54]^[59] PTH secretion exhibits a circadian rhythm, with levels peaking at night (around midnight) and reaching a nadir in the early morning, reflecting synchronization with calcium homeostasis and sleep-wake cycles.^[60] Seasonal variations also occur, with PTH concentrations approximately 7% higher in winter than in summer, inversely correlated with sunlight exposure and vitamin D levels.^[61] Recent advances include high-sensitivity third-generation assays, which offer improved accuracy in CKD by measuring only the 1-84 PTH form and excluding interfering fragments that over 40-50% inflate second-generation results in uremic patients, enabling earlier detection of secondary hyperparathyroidism.^[62]^[63] These assays correlate strongly with bone turnover markers and support guideline-recommended targets for CKD-mineral and bone disorder management.^[54]

Therapeutic Applications

Parathyroid hormone (PTH) and its analogs are primarily utilized in the treatment of osteoporosis and hypoparathyroidism, leveraging their anabolic effects on bone and regulatory roles in calcium homeostasis. Teriparatide, a synthetic analog of the N-terminal fragment of human PTH (PTH 1-34), was approved by the U.S. Food and Drug Administration (FDA) in November 2002 for the treatment of osteoporosis in postmenopausal women at high risk for fracture, as well as in men with osteoporosis and individuals with glucocorticoid-induced osteoporosis.^[64] Administered via daily subcutaneous injection, teriparatide promotes bone formation by intermittently stimulating osteoblasts, leading to increased bone mineral density and reduced fracture risk, with treatment limited to 24 months due to potential osteosarcoma risk observed in animal studies.^[65] Abaloparatide, an analog of parathyroid hormone-related protein (PTHrP 1-34), received FDA approval in 2017 for the treatment of postmenopausal women with osteoporosis at high risk for fracture.^[66] Similar to teriparatide, it is given as a daily subcutaneous injection and exhibits anabolic effects on bone, with clinical trials demonstrating superior reductions in vertebral fractures compared to placebo and comparable efficacy to teriparatide, alongside a potentially lower risk of hypercalcemia.^[67] For hypoparathyroidism, recombinant human PTH (1-84), marketed as Natpara, was approved by the FDA in 2015 as an adjunct to calcium and vitamin D to control hypocalcemia but carries a black box warning for osteosarcoma risk.^[68] Due to ongoing manufacturing challenges and supply constraints, Takeda announced the global discontinuation of Natpara production, with no shipments after December 31, 2025, leaving a gap in approved PTH replacement therapies in the U.S. and EU.^[69] Emerging PTH-based therapies address these limitations, particularly for hypoparathyroidism. Palopegteriparatide (TransCon PTH), a long-acting prodrug of PTH 1-34, was approved by the UK's Medicines and Healthcare products Regulatory Agency (MHRA) in April 2024 under the brand name Yorvipath for adults with chronic hypoparathyroidism, enabling once-daily subcutaneous administration that provides sustained PTH levels. It was also approved by the U.S. FDA in August 2024 for the treatment of adults with hypoparathyroidism. Phase 3 PaTHway trial results from 2025 confirmed its sustained efficacy over 52 weeks, with 81% of patients achieving serum calcium normalization without hypercalciuria and improvements in renal function persisting through 3 years of pooled data.^[70]^[71]^[72]^[73] Continuous subcutaneous infusion of PTH 1-34 via insulin pump systems offers an alternative for hypoparathyroidism management, mimicking physiologic PTH pulsatility and reducing reliance on oral calcium and vitamin D.^[74] Studies in adults and children demonstrate that pump delivery stabilizes serum calcium, lowers urinary calcium excretion, and normalizes bone turnover markers more effectively than twice-daily injections, with total daily PTH doses often 20-50% lower.^[75]^[76] Encaleret, an oral calcilytic that activates the calcium-sensing receptor to stimulate endogenous PTH secretion, showed promising phase 2 results in 2025 for post-surgical hypoparathyroidism, achieving normalization of serum and urinary calcium in 76-80% of patients within days while reducing hypercalciuria independent of PTH levels.^[77]^[78] No serious adverse events were reported, supporting its advancement to phase 3 trials as a non-injectable option.^[79]

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Aug 11, 2025 · Adults: 3.0-4.5 mg/dL or 0.97-1.45 mmol/L (SI units). Older adults: Values slightly lower than those in adults. Children: 4.5-6.5 mg/dL or 1.45- ...
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Physiologic and pathophysiologic roles of extra renal CYP27b1
PTH stimulates CYP27b1 expression principally by acting on its membrane receptor to promote cyclic AMP formation, PKA activation, and enhanced binding of CCAAT ...
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A parathyroid hormone/salt-inducible kinase signaling axis controls ...
Mar 2, 2023 · Together, these results demonstrated a PTH/SIK/CRTC signaling axis in the kidney that controls Cyp27b1 expression and 1,25-vitamin D synthesis.
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Vitamin D Metabolism, Mechanism of Action, and Clinical Applications
Feb 13, 2014 · CYP27B1 is the only enzyme responsible for the subsequent 1α-hydroxylation to 1,25(OH)2D. The renal CYP27B1 is likely responsible for most of ...Vitamin D Mechanism Of... · Vitamin D Analogs · Clinical Applications
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Feb 8, 2024 · Calcitriol (1,25(OH)2D3) regulates active calcium intestinal absorption by upregulating the brush border membrane calcium transporter TRPV6.
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Calcitriol, calcidiol, parathyroid hormone, and fibroblast growth ...
The low iCa concentration stimulates PTH production, but the increased PTH is unable to upregulate calcitriol synthesis due to a lack of functional tubules.<|control11|><|separator|>
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Mechanism of calcitriol regulating parathyroid cells in secondary ...
Oct 3, 2022 · Study has shown that 1,25(OH)2D3 can increase the expression of CaSR in the parathyroid, thyroid, and kidney by binding to RXR/VDR on VDREs in ...<|control11|><|separator|>
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[PDF] Minireview - Experimental Biology and Medicine
Calcitriol increases blood calcium and phosphate levels by increasing absorption from the intestine, and resorption of bone. Calcitriol synthesis is a multistep ...
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Regulation of Renal and Extrarenal Calcitriol Synthesis and Its ...
In addition to FGF23, the activity of CYP27B1 is suppressed by its end product calcitriol, while CYP24A1 is suppressed in the presence of PTH, and CYP27B1 is ...
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Primary hyperparathyroidism is an endocrine disorder characterized by increased parathyroid hormone secretion, leading to hypercalcemia and renal and skeletal ...Missing: magnesium | Show results with:magnesium
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Primary hyperparathyroidism is a common endocrine disorder caused by overactivation of parathyroid glands resulting in excessive release of parathyroid hormone.
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Also, vitamin D suppresses PTH secretion from parathyroid glands and regulates the calcium and phosphorus levels.[6]. Fibroblast growth factor 23 (FGF-23) is ...Missing: magnesium calcitonin
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Patients with both diseases also can become symptomatic. Untreated secondary HPT leads to progressive bone disease, osteitis fibrosa cystica, and soft-tissue ...
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Feb 24, 2024 · Hypoparathyroidism is an uncommon endocrine abnormality in which parathyroid gland dysfunction causes parathyroid hormone deficiency.
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Thus far, over 400 mutations within the GNAS coding region have been identified as causes of PHP 1a.[11] The mutations identified include frameshift ...
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Normocalcemic primary hyperparathyroidism (PHPT) is a newer phenotype of PHPT defined by elevated PTH concentrations in the setting of normal serum calcium ...Missing: endocrine. | Show results with:endocrine.
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Clinical Guidelines and PTH Measurement: Does Assay Generation ...
The plasma half-life of full-length PTH is very short (2 to 4 minutes), but the half-life of C-terminal fragments is five to ten times longer with normal ...Missing: degradation | Show results with:degradation
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A method comparison of the Roche intact PTH method versus the ...
Jun 23, 2025 · This study aimed to compare the second-generation Roche intact PTH method with the third-generation Roche whole PTH (1-84) method, examining differences based ...
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[PDF] The path to the standardization of PTH - CDC Stacks
This “second-generation” assay, along with the subsequent automated chemiluminescent, ELISA and IRMA methods, were globally called “intact” PTH assays as ...
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Comparison of Intact PTH Assay and Whole PTH Assay in Long ...
Intact PTH assay detects 7-84 PTH fragments, while whole PTH assay detects only 1-84 PTH. Whole PTH levels were lower, and intact PTH may overestimate PTH ...
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Reference Range. Adults (serum):. C-terminal and midmolecule: 50-330 pg/mL (50-330 ng/L); N-terminal: 8-24 pg/mL (8-24 ng/L); Intact molecule: 10-65 pg/mL (10- ...
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Jan 3, 2019 · In this paper, we highlight the importance of PTH standardization and the impact of establishing robust reference ranges for the accurate interpretation of PTH ...
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The circadian rhythm of calcium and bone homeostasis in Maasai
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The impact of seasonal variation of 25-hydroxyvitamin D and ...
PTH levels were significantly lower (7%) in summer than in winter. The mean serum concentration of calcium was 1% higher in August than in February, however not ...
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and Third-Generation Parathyroid Hormone Test Results in Patients ...
Nov 5, 2020 · In patients with chronic kidney disease (CKD), secondary hyperparathyroidism is assessed by measuring serum parathyroid hormone (PTH) levels.
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Serum parathyroid hormone (PTH) concentration of patients with chronic kidney disease (CKD) should be measured regularly and maintained within target ranges.
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IN NOVEMBER 2002, the Food and Drug Administration (FDA) approved teriparatide (Forteo) for the treatment of osteoporosis. Teriparatide contains the first 34 ...
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Apr 6, 2020 · FORTEO is indicated for the treatment of men and women with osteoporosis associated with sustained systemic glucocorticoid therapy (daily dosage ...
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Jan 29, 2024 · Abaloparatide, a synthetic peptide analog of parathyroid hormone-related protein (PTHrP), is used to manage and treat osteoporosis.Continuing Education Activity · Indications · Mechanism of Action · Administration
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Abaloparatide (Parathyroid Hormone Related-Protein, PTHrP ...
Abaloparatide is approved by the FDA for the treatment of osteoporosis, and ... Abaloparatide is a human parathyroid hormone related peptide [PTHrP(1-34)] analog, ...
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NATPARA® (parathyroid hormone) for Hypoparathyroidism
NATPARA treatment for hypoparathyroidism will be discontinued by the end of 2025. See Important Safety Info & Warning for possible risk of bone cancer.Healthcare Professionals · Important Safety Information · Contact Us · Get StartedMissing: recombinant 1-84
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Takeda's Discontinuation of NATPARA® (parathyroid hormone)
This means that no NATPARA shipments will be sent after December 31, 2025. This decision follows the previously communicated global manufacturing ...Missing: recombinant 1-84
[69]
United Kingdom's MHRA Approves YORVIPATH ...
Apr 24, 2024 · United Kingdom's MHRA Approves YORVIPATH® (palopegteriparatide) in Great Britain for the Treatment of Adults with Chronic Hypoparathyroidism.
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Mar 17, 2025 · Conclusion: At week 52 of the PaTHway trial, TransCon PTH showed sustained efficacy, safety, and tolerability in adults with hypoparathyroidism.
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https://www.fda.gov/news-events/press-announcements/fda-approves-new-drug-treat-rare-disorder-hypoparathyroidism
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Mar 29, 2024 · Continuous subcutaneous infusion of recombinant parathyroid hormone (rhPTH) through a pump has been proposed as a therapeutic alternative for patients with ...Missing: systems | Show results with:systems
[73]
Continuous Subcutaneous Delivery of rhPTH(1-84) and rhPTH(1-34 ...
While the use of pump therapy with human PTH(1-34) [hPTH(1-34)] is not FDA approved, it has been shown to be effective for treatment of hypoparathyroidism in ...Abstract · Methods · Results · Discussion
[74]
Effects of Pump versus Twice-Daily Injection Delivery of Synthetic ...
Compared with twice-daily delivery, pump delivery of PTH 1-34 provides more physiologic calcium homeostasis and bone turnover in children with severe ...<|control11|><|separator|>
[75]
Encaleret Showed Parathyroid Hormone ... - BridgeBio Pharma Inc.
Sep 6, 2025 · The Phase 2 results were shared in an oral presentation at the American Society for Bone and Mineral Research (ASBMR) Annual Meeting 2025.Missing: calcilytic | Show results with:calcilytic
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Oct 29, 2025 · Findings showed 76% of patients treated with encaleret met the primary endpoint, achieving both blood and urine calcium levels within the target ...Missing: calcilytic | Show results with:calcilytic
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Encaleret Normalizes Calcium in Phase 2 Hypoparathyroidism
Sep 9, 2025 · Nine participants showed a rapid and sustained reduction in fractional excretion of calcium. No serious adverse events were reported over the ...Missing: calcilytic | Show results with:calcilytic