Lack of GNAS re-methylation during oogenesis may be a cause of sporadic pseudohypoparathyroidism type Ib (PHP1B)

Context Pseudohypoparathyroidism type Ib (PHP1B) is characterized by hypocalcemia and hyperphosphatemia due to PTH-resistance in the proximal renal tubules. Maternal pathogenic STX16/GNAS variants leading to maternal epigenetic GNAS changes impair expression of the stimulatory G protein alpha-subunit (Gsα) thereby causing autosomal dominant PHP1B (AD-PHP1B). In contrast, genetic defects responsible for sporadic PHP1B (sporPHP1B) remain mostly unknown. Objective Determine whether PHP1B encountered after in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) causes GNAS re-methylation defects similar to those in sporPHP1B. Design Retrospective analysis. Results Nine among thirty-six sporPHP1B patients investigated since 2000, all with LOM at the three maternal GNAS DMRs and gain-of-methylation (GOM) at the paternal NESP DMR, had been conceived through IVF or ICSI. Besides abnormal GNAS methylation, IVF/ICSI-PHP1B cases revealed no additional imprinting defects. Three of these PHP1B patients have dizygotic twins and four have IVF/ICSI-conceived siblings, all with normal GNAS methylation; two unaffected younger siblings were conceived naturally. Conclusion Sporadic and IVF/ICSI-conceived PHP1B patients revealed indistinguishable epigenetic changes at all four GNAS DMRs thus suggesting a similar underlying disease mechanism. Given that re-methylation at the three maternal DMRs occurs during oogenesis, male factors are unlikely to cause LOM post-fertilization. Instead, at least some of the sporPHP1B variants could be caused by a defect(s) in an oocyte-expressed gene that is required for fertility and for re-establishing maternal GNAS methylation imprints. It remains uncertain, however, whether lack of GNAS re-methylation alone impairs oocyte maturation because of insufficient Gsα expression, thus necessitating Assisted Reproductive Technology (ART) for conception.

Progression of PTH-resistance in autosomal dominant pseudohypoparathyroidism type Ib due to maternal STX16 deletions

Context Maternally inherited STX16 deletions that cause loss-of-methylation at GNAS exon A/B and thereby reduce Gsα expression are the most frequent cause of autosomal dominant pseudohypoparathyroidism type 1B (AD-PHP1B). Early identification of these disease-causing variants in the children of affected and unaffected female carriers would prompt treatment with calcium and calcitriol, once PTH levels increase, thereby preventing hypocalcemia and associated complications. Objectives Determine when PTH and calcium abnormalities develop after birth if a STX16 deletion is inherited maternally. Patients and Methods Forty-four children of affected (n=7) or unaffected (n=7) females with a STX16 deletion were investigated for the presence of these variants. If a deletion was identified, measurement of PTH, calcium, phosphate, and TSH was advised. Results The STX16 deletion that causes AD-PHP1B was identified in 25 children. Pre-treatment laboratory results were available for 19 of those cases. Elevated PTH levels were detected by 2 years of age and these were progressively higher if laboratory testing was first performed after establishing the genetic defect later in life. Total serum calcium levels remained within normal limits until about five years of age. TSH levels showed no consistent rise over time. Conclusion Establishing whether a STX16 deletion is inherited from a female carrier of a disease-causing variant rapidly establishes the diagnosis of AD-PHP1B. Several years before overt hypocalcemia developed, PTH levels increased thereby establishing the onset of PTH-resistance. Our findings provide diagnostic guidance and when treatment with calcium and calcitriol should be considered, in order to prevent hypocalcemia and associated sequelae.

Rare Case of Severe Hypocalcemia Due to PTH Resistance Related to Diet Pill

Introduction: The production of parathyroid hormone (PTH) is essential for calcium the maintenance of normal mineral metabolism. Parathyroid cells have cell-surface calciumsensing receptors, even small changes in extracellular Ca induce rapid changes in PTH secretion. Hypocalcaemia is a well-recognized manifestation of magnesium deficiency. We present rare case of severe hypocalcemia due to PTH resistance caused by hypomagnesemia related to diet pill. Case Report: 61 year old Hispanic obese female with chronic gastritis on omeprazole 20 mg daily, no other significant past medical and surgical history, not taking any prescribed medications presents to ED with complaints of tingling and numbness around the mouth, abdominal cramps, chest pain, shortness of breath and anxiety. On arrival calcium was found to be 6.0mg/dl(8.2–10.2mg/dl) with ionized calcium of 0.60mmol/l(1.13-1.32mmol/l) and EGFR>90ml/min, Albumin-4.0g/l, Magnesium-1.1mg/dl(1.6–2.3mg/dl), Phosphorus-6.1mg/dl(2.4–4.5mg/dl),rest of the electrolytes were normal. Patient was given IV calcium gluconate 2g and magnesium which helped improving her symptoms. PTH was 1700pg/ml(23-73pg/ml), low Vitamin D 25-hydroxy 20ng/dl(30-100ng/dl). Urinary calcium was <1mg/dl(2.0–17.5mg/dl). Vitamin D1,25- dihydroxy 34pg/ml(18-78pg/ml), PTH-like peptide levels 0.6pmol/l(<4.2pmol/l). EKG was normal no QT interval changes. For 4 weekspatient was taking weight loss medication was given to her by her brother called nucific-bio-x4. Patient had lost 4 pounds while taking the medication and had suppression of appetite. Physical features of pseudohypoparathyroidism were not seen. Patient had poor dietary intake of calcium, denied taking vitamin D supplements. Patient was given calcium acetate 2001 mg TID with meals, calcitriol 0.5mcg daily and calcium gluconate 2g IV intermittently was given. That improved her calcium levels to 6.8mg/dl with ionized calcium-0.90mmol/l. Magnesium was replaced IV and discharged on magnesium oxide 400mg BID to maintain magnesium the normal range. The patient was given loading dose of ergocalciferol 50,000 IUfor 8 weeks. At the time of discharge repeat PTH levels were 1600 pg/ml and calcium levels were 8.2mg/dl. 3D CT of the neck did not parathyroid mass. After discharge patient continued on oral calcium and magnesium to maintain calcium levels between 8.4–10.2mg/dl. After discharge calcium levels were 8.6mg/dl, vitamin D 25-hydroxy levels were 32ng/dl and maintenance dose of vitamin D3 2000 IU daily also continued. Nucific-bio-x4 pill was discontinued. Conclusion: In conclusion, severe life threatening hypocalcemia can occur with unsupervised weight lossmedications due to malabsorption of magnesium in patient with likely mutation in magnesium receptors causing PTH resistance. Vitamin D deficiency worsens hypocalcemia resulting into secondary hyperparathyroidism.

MO584TRABECULAR BONE SCORE AND BONE MICROARCHITECTURE IN HEMODIALYSIS PATIENTS. ITS POTENTIAL RELATIONSHIP WITH PTH-RESISTANCE : A PILOT STUDY

Background and Aims To explore:i)differences in predictive variables between TrabecularBoneScore(TBS)-derived and LumbarT-score derived bone types.ii)the relationship difference of TBS and LumbarT-score with various ranges of PTH levels in order to identify the levels of PTH that overcome PTH resistance iii) to conform normal upper limit of PTHi levels in hemodialysis patients recommended by K-DIGO guidelines. Method In twenty-five hemodialysis patients,following variables were recorded:biochemical variables,DXA derived variables(including TBS),FRAX-tool derived HRs.The relationship of variables with TBS-derived and LumbarTscore-derived bone types was tested by univariate analysis. The association of TBS,LumbarTscore and fracture HRs with PTHi was tested by univariate analysis and regression curve fitting(maximizing R²). Results Using univariate analysis,the predictive variables of lumbarT-score derived and TBS-derived bone types are different.By curve fitting regression TBS vs PTHi had a sinusoidal pattern with higher values,correlating to PTHi values in the 4th quartile(462 pg/ml (341 -696)corresponding to the normal levels recommended by K-DIGO guidelines.In the same range of values,LumbarT-score vs PTHi for BMD-derived bone type has a progressively increasing trend for osteopenia and osteoporosis,with a statistically significant difference(P0.008). Conclusion The predictive variables of TBs-derived and LumbarT-score derived bone types are different.Bone microarchitecture(MA),measured by TBS,correlates oppositely than LumbarT-score with higher PTHi values in the normal range of PTHi levels recommended by the K-DIGO-CKD-MBD2009-2017 guidelines.Within this range,PTHi values overcome PTH-resistance and improve the bone mineral metabolism. Results must not be extended to higher or lower levels of PTHi compared to those considered in the study for which there is a clear evidence of increase in the relative risk of mortality.

A novel GNAS mutation inherited from probable maternal mosaicism causes two siblings with pseudohypoparathyroidism type 1A

ObjectivesObjectives Pseudohypoparathyroidism type 1A (PHP1A) is caused by maternal inheritance of GNAS mutations. It is characterized by the resistance to several hormones, primarily the parathyroid hormone (PTH), and the features of Albright’s hereditary osteodystrophy.Case presentationHere, we present a family comprised two affected brothers with PHP1A and identify a novel mutation (c.277C>T) in the GNAS gene. The siblings developed a slightly different presentation in the same clinical condition. Although both patients presented with PTH resistance, which is the hallmark of PHP, the proband showed the thyroid-stimulating hormone resistance with the progression of heterotopic ossification from skin and subcutaneous tissue into deep connective tissue, while the younger brother with normocalcemia did not show the resistance to other hormones. The patients may inherit the mutation from their mother who presumably carries the mutation as a mosaicism.ConclusionsOur case highlights the significance of considering mosaicism as an explanation for apparent de novo cases of pseudohypoparathyroidism.

Congenital Hypoparathyroidism Associated With Elevated Circulating Nonfunctional Parathyroid Hormone Due to Novel PTH Mutation

Context Familial hypoparathyroidism has a heterogeneous presentation where patients usually have low parathyroid hormone (PTH) levels due to impaired production or secretion. This contrasts with pseudohypoparathyroidism, in which PTH resistance is usually associated with an elevated serum PTH. High levels of circulating PTH can also be due to bioinactive PTH, which is difficult to distinguish from pseudohypoparathyroidism on biochemical grounds. Case Description We report on 2 sisters from consanguineous parents who presented with tetany at birth and were diagnosed with congenital hypocalcemia. Serum PTH levels were normal for many years, but progressively increased in midadulthood to greater than 100x the upper limit of normal on multiple assays. Homozygosity mapping was performed on 1 sister that demonstrated loss of heterozygosity (LOH) around PTH. Sequencing revealed a previously unreported variant, c.94T>C, predicting a codon change of p.Ser32Pro that is biologically inactive. Conclusions This case report shows a previously unreported unusual biochemical phenotype of a rising PTH in the context of a novel PTH mutation. This expands the evolving genotypes associated with hypoparathyroidism without established gene mutations.

SAT-343 Diagnosis and Management of Pseudohypoparathyroidism Type 1B

Background: Pseudohypoparathyroidism (PHP) is a heterogeneous group of disorders characterized by end-organ resistance to PTH. Most subtypes are caused by pathogenic variants or epigenetic alterations in GNAS, which encodes the alpha subunit of the G protein regulating end-organ response to PTH. PHP type 1B (PHP1B) is caused by methylation defects in GNAS and presents with isolated renal PTH resistance. Clinical Case: A 29-year-old gentleman presented with intermittent muscle spasms, perioral and digital paresthesias, fatigue, and anxiety. Family history was notable for similar symptoms in his sister and nephew. Physical examination revealed normal stature, non-dysmorphic facies, and no soft tissue ossifications or skeletal anomalies. Chvostek sign was positive. Laboratory studies showed total calcium 6.0 mg/dL (n 8.6–10.0 mg/dL), phosphorus 6.8 mg/dL (n 2.5–3.5 mg/dL), creatinine 0.8 mg/dL (n 0.8–1.3 mg/dL), albumin 5.0 (n 3.5–5.0 mg/dL), PTH 231 pg/mL (n 15–65 pg/mL), total 25-hydroxyvitamin D 19 mg/mL (n 20–50 ng/mL), and 1,25-dihydroxyvitamin D 45 pg/mL (n 18–64 pg/mL). Additional endocrine testing showed TSH 6.4 mIU/L (n 0.3–4.2 mIU/L), free T4 1.1 ng/dL (n 0.9–1.7 ng/dL), and TPO antibody <0.3 IU/mL (n <9.0 IU/mL). Renal ultrasound was normal. CT head showed diffuse intracranial calcifications. He was diagnosed with PHP1B and started on calcitriol, cholecalciferol, and calcium carbonate. He declined genetic testing. Repeat laboratory studies were improved with total calcium 8.5 mg/dL, phosphorus 3.9 mg/dL, total 25-hydroxyvitamin D 49 mg/mL, PTH 124 pg/mL, and 24-hour urinary calcium 269 mg (n <250 mg). Conclusion: International consensus guidelines for the diagnosis and management of PHP and related disorders were recently published by Mantovani et al. in 2018. Proposed clinical and biochemical major criteria include PTH resistance, ectopic ossifications, early-onset obesity, TSH resistance, and Albright hereditary osteodystrophy (AHO; round facies, short stature, brachydactyly, developmental delay). Unlike PHP type 1A, PHP1B often presents later in life and features of AHO are usually absent, so diagnosis requires a high degree of clinical suspicion. It is recommended that patients with suspected PHP have molecular confirmation with sequencing, methylation, and/or copy number variant analysis of GNAS. Routine monitoring of calcium, phosphorus, and PTH levels and treatment with active vitamin D analogues with or without calcium supplements are advised to maintain normal calcium and phosphorus and PTH <2 times the upper limit of normal. Other recommendations include renal imaging for nephrocalcinosis, eye exam for cataracts, CT head imaging (in patients with neurological findings) for calcifications, regular dental care, and management of comorbid endocrinopathies. A multidisciplinary approach is needed in this complex, heterogeneous group of disorders.

OR07-01 Identification of the First Case of Acquired Autoimmune Parathyroid Hormone (PTH) Resistance Due to PTH1 Receptor (PTH1R) Autoantibodies

Background: Here we describe a patient who presented with symptomatic hypocalcemia and a biochemical picture suggestive of PTH resistance. PTH resistance is a hallmark of pseudohypoparathyroidism, a heterogeneous group of rare disorders caused by genetic or epigenetic alterations of PTH/PTHrP signaling. However, PTH receptor-related autoimmune etiology has not been identified as the underlying mechanism for PTH resistance. Here we describe the first case of acquired autoimmune PTH resistance that is secondary to PTH1R autoantibodies. Clinical Case: A 60-year-old African-American woman, who previously had normal calcium homeostasis, presented with acute, symptomatic hypocalcemia, hyperphosphatemia and markedly elevated serum PTH, consistent with parathyroid hormone resistance. She did not have other hormone resistance or a clinical phenotype suggestive of pseudohypoparathyroidism. Whole-exome sequencing and GNAS methylation analysis revealed no genetic or epigenetic defects of the PTH/PTHrP signaling pathway. Treatment with Calcitriol and Calcium supplements was initiated with good clinical response. Within 10 years of follow-up, the patient developed autoimmune hypothyroidism, alopecia and an unusual form of membranous glomerulonephritis, raising the suspicion for an autoimmune etiology for PTH resistance. Luciferase immunoprecipitation system assay identified antibodies against PTH1R with mapping to the N-terminal extracellular ligand-binding domain (amino acids 1- 178). Using an in vitro biological assay in GP-2.3 cells, we found that the antibodies derived from the patient’s serum blocked PTH downstream signaling via Gsalpha/cAMP/protein kinase A pathway in a concentration-dependent manner. The patient’s autoantibody profile led to the diagnosis of additional autoimmune diseases, including atrophic gastritis and Sjogren syndrome. Lymphocyte immunophenotyping using flow cytometry revealed an overall normal B and T cell profile, but with decreased frequencies and numbers of switched and non-switched memory B cell subsets and an increased frequency and number of the CD8+ naïve cell population. Genes associated with autoimmune inflammatory disorders were sequenced but no pathologic changes were detected. Conclusions: Identification of the first case of autoimmune PTH resistance secondary to PTH1R autoantibodies extends the etiologic spectrum of hypoparathyroidism and should be considered when a patient presents with findings consistent with pseudohypoparathyroidism, especially in the presence of additional autoimmune diseases.

SAT-371 Severe Hypocalcemia Secondary to Pseudohypoparathyroidism

Introduction: Pseudohypoparathyroidism (PHP) is a rare disorder characterized by PTH resistance due to a mutation in the GNAS gene causing decreased cyclic AMP generation. The 5 subtypes of PHP include type 1a, 1b, 1c, 2, and pseudo-PHP with type 1a being the most common. Patients with PHP present with hypocalcemia, hyperphosphatemia, appropriately elevated PTH, and suppressed calcitriol levels. PHP type 1a patients have characteristic features including obesity, short stature, round facies, and shortened metacarpals. PHP patients should be evaluated for other endocrinopathies as mutations in the GNAS gene may result in resistance to other hormones like TSH, GHRH, and gonadotropins. Case Report: This patient is a 25 year old male who presented to clinic for evaluation of hypocalcemia. He denied any personal or family history of calcium disorders, thyroid disease, or parathyroid disease. He admitted to severe fatigue and muscle cramps for over one year leading to a car accident. He was sent to the emergency room and diagnosed with hypocalcemia requiring IV calcium gluconate. He was then seen by his family physician and was found to have elevated intact PTH and low 25-hydroxy vitamin D levels. He was placed on cholecalciferol 5000 international units (IU) daily, ergocalciferol 50,000 IU once weekly, calcium carbonate 500 mg (6 tablets daily), and referred to endocrinology. The physical exam was unremarkable. The laboratory values tested were an intact PTH of 645 pg/mL (10–65 pg/mL), ionized calcium of 4.2 mg/dL (4.6–5.08 mg/dL), magnesium of 2.1 mg/dL (1.5–2.3 mg/dL), 25-OH vitamin D of 31.7 ng/mL (20–100 ng/mL), and creatinine of 0.81 mg/dL (0.7–1.3 mg/dL) four months after starting the above mentioned calcium and vitamin D supplementation. Further testing revealed a phosphorus level of 4.8 mg/dL (2.3–4.7 mg/dL), calcitriol level of 55.8 pg/mL(19.9–79.3 pg/mL), TSH of 10.46 uIU/mL (0.4–4.2 uIU/mL) and free T4 of 1.5 ng/dL (0.8–1.7 ng/dL). His labs were consistent with PHP. Although unknown which PHP subtype, it is likely not type 1a as he lacks its characteristic phenotype. His abnormal thyroid function tests may be secondary to TSH resistance associated with the GNAS gene mutation. He was told to continue the current dose of calcium carbonate but to discontinue ergocalciferol and cholecalciferol. He was placed on calcitriol 0.5 mcg daily. He will have repeat levels of his ionized calcium, calcitriol, TSH, and free T4 in two weeks. If TSH is still above 10 uIU/mL, we will start levothyroxine replacement. Conclusion: Although a rare disorder, clinicians should have a high index of suspicion for PHP to prevent complications of hypocalcemia (tetany, arrhythmias, seizures) and metabolic bone disease from PTH resistance. References: Mantovani, G. Pseudohypoparathyroidism: Diagnosis and Treatment, The Journal of Clinical Endocrinology & Metabolism, Volume 96, Issue 10, 1 October 2011, Pages 3020–3030.