Pseudohypoparathyroidism Type 1b Research Articles

Recurrent Small Variants in NESP55/NESPAS Associated with Broad GNAS Methylation Defects and Pseudohypoparathyroidism Type 1b.

Pseudohypoparathyroidism type 1B (PHP1B) is associated with epigenetic changes on the maternal allele of the imprinted GNAS gene that inhibit expression of the alpha subunit of Gs (Gsα), thereby leading to parathyroid hormone resistance in renal proximal tubule cells where expression of Gs from the paternal GNAS allele is normally silent. Although all patients with PHP1B show loss of methylation for the exon A/B differentially methylated region (DMR), some patients with autosomal dominant PHP1B (AD-PHP1B) and most patients with sporadic PHP1B have additional methylation defects that affect the DMRs corresponding to exons XL, AS1, and NESP. Because the genetic defect is unknown in most of these patients, we sought to identify the underlying genetic basis for AD-PHP1B in two multigenerational families with broad GNAS methylation defects and negative clinical exomes. Genome sequencing identified small GNAS variants in each family that were also present in unrelated PHP1B subjects in a replication cohort. Maternal transmission of one GNAS microdeletion showed reduced penetrance in some unaffected patients. Expression of AS transcripts was increased, and NESP was decreased, in cells from affected patients. These results suggest that the small deletion activate AS transcription leading to methylation of the NESP DMR with consequent inhibition of NESP transcription, and thereby provide a potential mechanism for PHP1B.

#191 An unusual cause of hypocalcemia in a young patient

Abstract Background and Aims A 33-year-old man visited the Nephrology Department outpatient clinic with abnormal laboratory findings: his serum calcium level was 5.9 mg/dL in a recent health examination. He denied any underlying disease and was on no medications. He complained of a tingling sensation in his hands and of eyelid twitching. On physical examination, he showed Chvostek's sign. His laboratory findings including serum calcium level are shown in Table 1. He did not have any morphological abnormalities, such as a round face, brachydactyly, or dental anomalies. Method Since he showed hypocalcemia, normal 25-hydroxyvitamin D, and elevated parathyroid hormone (PTH) levels, the presence of PTH resistance was presumed. Under strong suspicion of pseudohypoparathyroidism (PHP) in this patient, DNA sequence analysis and methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) of GNAS and STX16, genetic regions that are often affected by mutations or imprinting changes in PHP, was performed. No pathogenic mutations in GNAS and STX16 were detected by sequencing. Results Results of MS-MLPA of the GNAS locus demonstrated abnormal methylation patterns in the patient after HhaI restriction enzyme treatment. The methylation ratio showed a gain of methylation in the NESP55 region and loss of methylation in the AS, XL, and A/B differentially methylated regions (DMRs) in the patient as compared to a healthy control (Fig. 1). The patient was diagnosed with PHP type 1B (PHP1B) due to the methylation abnormalities in multiple DMRs. His parents both showed normal serum calcium levels; thus, no further genetic testing was conducted. He is on outpatient follow-up with adequate calcium replacement and no specific symptoms. Conclusion PHP is a rare disorder of unknown prevalence. It is characterized by hypocalcemia, hyperphosphatemia, and increased PTH levels. PHP1B is a subtype of PHP characterized by isolated renal PTH resistance, usually without physical abnormalities such as Albright hereditary osteodystrophy or other endocrine abnormalities. PHP1B can be sporadic or familial. The genetic characteristics of most sporadic PHP1B remains unclear, but GNAS imprinting abnormalities and hypomethylation at the A/B DMRs have been reported. Symptoms of PHP1B usually begin in childhood due to low calcium levels and may include numbness, seizures, tetany, cataracts, and dental problems. However, as in our case, specific symptoms may not occur until adulthood. Therefore, when evaluating the cause of hypocalcemia, it is necessary to differentiate PHP1B, even in adults, and particularly in cases with hyperphosphatemia and high PTH levels.

GNAS AS2 methylation status enables mechanism-based categorization of pseudohypoparathyroidism type 1B.

Pseudohypoparathyroidism type 1B (PHP1B) results from aberrant genomic imprinting at the GNAS gene. Defining the underlying genetic cause in new patients is challenging because various genetic alterations (e.g., deletions, insertions) within the GNAS genomic region, including the neighboring STX16 gene, can cause PHP1B, and the genotype-epigenotype correlation has not been clearly established. Here, by analyzing patients with PHP1B with a wide variety of genotypes and epigenotypes, we identified a GNAS differentially methylated region (DMR) of distinct diagnostic value. This region, GNAS AS2, was hypomethylated in patients with genetic alterations located centromeric but not telomeric of this DMR. The AS2 methylation status was captured by a single probe of the methylation-sensitive multiplex ligation-dependent probe amplification (MS-MLPA) assay utilized to diagnose PHP1B. In human embryonic stem cells, where NESP55 transcription regulates GNAS methylation status on the maternal allele, AS2 methylation depended on 2 imprinting control regions (STX16-ICR and NESP-ICR) essential for NESP55 transcription. These results suggest that the AS2 methylation status in patients with PHP1B reflects the position at which the genetic alteration affects NESP55 transcription during an early embryonic period. Therefore, AS2 methylation levels can enable mechanistic PHP1B categorization based on genotype-epigenotype correlation and, thus, help identify the underlying molecular defect in patients.

C-Cell Hyperplasia and Cystic Papillary Thyroid Carcinoma in a Patient with Type 1B Pseudohypoparathyroidism and Hypercalcitoninaemia: Case Report and Review of the Literature.

Hypercalcitoninaemia has been described in patients with pseudohypoparathyroidism (PHP) type 1A and 1B. Elevated calcitonin levels are thought to result from impaired Gsα receptor signaling, leading to multiple hormone resistance. Evidence on the risk of medullary thyroid carcinoma (MTC) or C-cell hyperplasia in PHP patients with hypercalcitoninaemia is lacking. A 43-year-old Caucasian man was referred to our endocrinology clinic for chronic hypocalcemia associated with elevated serum parathormone levels and a single cystic thyroid nodule. The patient did not show skeletal deformities, and screening for concomitant hormone resistances was negative, except for the presence of elevated serum calcitonin levels. The workup led to a molecular diagnosis of sporadic PHP1B. Fine needle aspiration of the thyroid nodule was not diagnostic. The calcium stimulation test yielded an abnormal calcitonin response. Given the scarcity of data on the risk of thyroid malignancy in PHP and calcium stimulation test results, total thyroidectomy was performed. Histological examination revealed cystic papillary thyroid cancer in a background of diffuse C-cell hyperplasia. To our knowledge, we are the first to describe a rare form of thyroid cancer combined with C-cell hyperplasia in a patient with PHP and hypercalcitoninaemia. In the present case, a mere receptor resistance might not fully explain the elevated calcitonin levels, suggesting that hypercalcitoninaemia should be carefully evaluated in PHP patients, especially in the case of concomitant thyroid nodules. Further studies on larger cohorts are needed to elucidate this topic.

(Epi)genetic and clinical characteristics in 84 patients with pseudohypoparathyroidism type 1B.

Pseudohypoparathyroidism type 1B (PHP1B) caused by methylation defects of differentially methylated regions (DMRs) on the GNAS locus can be categorized into groups according to etiologies and methylation defect patterns of the DMRs. The aim of this study was to clarify the clinical characteristics in each group. Comprehensive molecular analyses consisting of methylation, copy number, and microsatellite analyses. Eighty-four patients with PHP1B were included in this study. We classified them into five groups, namely, autosomal dominant inheritance-PHP1B (Group 1, G1), sporadic-PHP1B (G2), and atypical-PHP1B (G3-G5), based on the methylation defect patterns in four DMRs on the GNAS locus and etiologies and evaluated the clinical findings in each group and compared them among the groups. G2 had the youngest age and the highest serum intact parathyroid hormone levels among the five groups at the time of diagnosis. The most common symptoms at the time of diagnosis were tetany in G1, and seizures or loss of consciousness in G2. Albright's hereditary osteodystrophy and PHP-suggestive features were most frequently observed in the G2 proband. Nine patients had neurodevelopmental disorders (NDs) consisting of mild to borderline intellectual disability and/or developmental delay. There were no significant correlations between the average methylation ratios of seven CpG sites in the GNAS-A/B:TSS-DMR and hormonal and biochemical findings. This study revealed the differences in some clinical characteristics, particularly clinical features and ages at the time of diagnosis between G2 and other groups and detailed NDs observed in some patients with PHP1B.

Co-occurrence of Beckwith-Wiedemann syndrome and pseudohypoparathyroidism type 1B: coincidence or common molecular mechanism?

Imprinting disorders are congenital diseases caused by dysregulation of genomic imprinting, affecting growth, neurocognitive development, metabolism and cancer predisposition. Overlapping clinical features are often observed among this group of diseases. In rare cases, two fully expressed imprinting disorders may coexist in the same patient. A dozen cases of this type have been reported so far. Most of them are represented by individuals affected by Beckwith-Wiedemann spectrum (BWSp) and Transient Neonatal Diabetes Mellitus (TNDM) or BWSp and Pseudo-hypoparathyroidism type 1B (PHP1B). All these patients displayed Multilocus imprinting disturbances (MLID). Here, we report the first case of co-occurrence of BWS and PHP1B in the same individual in absence of MLID. Genome-wide methylation and SNP-array analyses demonstrated loss of methylation of the KCNQ1OT1:TSS-DMR on chromosome 11p15.5 as molecular cause of BWSp, and upd(20)pat as cause of PHP1B. The absence of MLID and the heterodisomy of chromosome 20 suggests that BWSp and PHP1B arose through distinct and independent mechanism in our patient. However, we cannot exclude that the rare combination of the epigenetic defect on chromosome 11 and the UPD on chromosome 20 may originate from a common so far undetermined predisposing molecular lesion. A better comprehension of the molecular mechanisms underlying the co-occurrence of two imprinting disorders will improve genetic counselling and estimate of familial recurrence risk of these rare cases. Furthermore, our study also supports the importance of multilocus molecular testing for revealing MLID as well as complex cases of imprinting disorders.

The long-range interaction between two GNAS imprinting control regions delineates pseudohypoparathyroidism type 1B pathogenesis.

Genetic defects of GNAS, the imprinted gene encoding the stimulatory G protein α-subunit, are responsible for multiple diseases. Abnormal GNAS imprinting causes pseudohypoparathyroidism type 1B (PHP1B), a prototype of mammalian end-organ hormone resistance. Hypomethylation at the maternally methylated GNAS A/B region is the only shared defect in patients with PHP1B. In autosomal dominant (AD) PHP1B kindreds, A/B hypomethylation is associated with maternal microdeletions at either the GNAS NESP55 differentially methylated region or the STX16 gene located approximately 170 kb upstream. Functional evidence is meager regarding the causality of these microdeletions. Moreover, the mechanisms linking A/B methylation and the putative imprinting control regions (ICRs) NESP-ICR and STX16-ICR remain unknown. Here, we generated a human embryonic stem cell model of AD-PHP1B by introducing ICR deletions using CRISPR/Cas9. With this model, we showed that the NESP-ICR is required for methylation and transcriptional silencing of A/B on the maternal allele. We also found that the SXT16-ICR is a long-range enhancer of NESP55 transcription, which originates from the maternal NESP-ICR. Furthermore, we demonstrated that the STX16-ICR is an embryonic stage-specific enhancer enabled by the direct binding of pluripotency factors. Our findings uncover an essential GNAS imprinting control mechanism and advance the molecular understanding of PHP1B pathogenesis.

Successful management of Pseudohypoparathyroidism Type 1b in pregnancy: a case report

Successful management of Pseudohypoparathyroidism Type 1b in pregnancy: a case report

PTH, FGF-23, Klotho and Vitamin D as regulators of calcium and phosphorus: Genetics, epigenetics and beyond.

The actions of several bone-mineral ion regulators, namely PTH, FGF23, Klotho and 1,25(OH)2 vitamin D (1,25(OH)2D), control calcium and phosphate metabolism, and each of these molecules has additional biological effects related to cell signaling, metabolism and ultimately survival. Therefore, these factors are tightly regulated at various levels – genetic, epigenetic, protein secretion and cleavage. We review the main determinants of mineral homeostasis including well-established genetic and post-translational regulators and bring attention to the epigenetic mechanisms that affect the function of PTH, FGF23/Klotho and 1,25(OH)2D. Clinically relevant epigenetic mechanisms include methylation of cytosine at CpG-rich islands, histone deacetylation and micro-RNA interference. For example, sporadic pseudohypoparathyroidism type 1B (PHP1B), a disease characterized by resistance to PTH actions due to blunted intracellular cAMP signaling at the PTH/PTHrP receptor, is associated with abnormal methylation at the GNAS locus, thereby leading to reduced expression of the stimulatory G protein α-subunit (Gsα). Post-translational regulation is critical for the function of FGF-23 and such modifications include glycosylation and phosphorylation, which regulate the cleavage of FGF-23 and hence the proportion of available FGF-23 that is biologically active. While there is extensive data on how 1,25(OH)2D and the vitamin D receptor (VDR) regulate other genes, much more needs to be learned about their regulation. Reduced VDR expression or VDR mutations are the cause of rickets and are thought to contribute to different disorders. Epigenetic changes, such as increased methylation of the VDR resulting in decreased expression are associated with several cancers and infections. Genetic and epigenetic determinants play crucial roles in the function of mineral factors and their disorders lead to different diseases related to bone and beyond.

Novel genetic variants of KHDC3L and other members of the subcortical maternal complex associated with Beckwith–Wiedemann syndrome or Pseudohypoparathyroidism 1B and multi-locus imprinting disturbances

BackgroundBeckwith–Wiedemann syndrome (BWS) and Pseudohypoparathyroidism type 1B (PHP1B) are imprinting disorders (ID) caused by deregulation of the imprinted gene clusters located at 11p15.5 and 20q13.32, respectively. In both of these diseases a subset of the patients is affected by multi-locus imprinting disturbances (MLID). In several families, MLID is associated with damaging variants of maternal-effect genes encoding protein components of the subcortical maternal complex (SCMC). However, frequency, penetrance and recurrence risks of these variants are still undefined. In this study, we screened two cohorts of BWS patients and one cohort of PHP1B patients for the presence of MLID, and analysed the positive cases for the presence of maternal variants in the SCMC genes by whole exome-sequencing and in silico functional studies.ResultsWe identified 10 new cases of MLID associated with the clinical features of either BWS or PHP1B, in which segregate 13 maternal putatively damaging missense variants of the SCMC genes. The affected genes also included KHDC3L that has not been associated with MLID to date. Moreover, we highlight the possible relevance of relatively common variants in the aetiology of MLID.ConclusionOur data further add to the list of the SCMC components and maternal variants that are involved in MLID, as well as of the associated clinical phenotypes. Also, we propose that in addition to rare variants, common variants may play a role in the aetiology of MLID and imprinting disorders by exerting an additive effect in combination with rarer putatively damaging variants. These findings provide useful information for the molecular diagnosis and recurrence risk evaluation of MLID-associated IDs in genetic counselling.

Sporadic Pseudohypoparathyroidism Type 1B in Monozygotic Twins: Insights Into the Pathogenesis of Methylation Defects

ContextSporadic pseudohypoparathyroidism type 1B (sporPHP1B) is an imprinting disease without a defined genetic cause, characterized by broad methylation changes in differentially methylated regions (DMRs) of the GNAS gene.ObjectiveThis work aims to provide insights into the causative event leading to the GNAS methylation defects through comprehensive molecular genetic analyses of a pair of female monozygotic twins concordant for sporPHP1B who were conceived naturally, that is, without assisted reproductive techniques.MethodsUsing the leukocyte genome of the twins and family members, we performed targeted bisulfite sequencing, methylation-sensitive restriction enzyme (MSRE)-quantitative polymerase chain reaction (qPCR), whole-genome sequencing (WGS), high-density single-nucleotide polymorphism (SNP) array, and Sanger sequencing.ResultsMethylation analyses by targeted bisulfite sequencing and MSRE-qPCR revealed almost complete losses of methylation at the GNAS AS, XL, and A/B DMRs and a gain of methylation at the NESP55 DMR in the twins, but not in other family members. Except for the GNAS locus, we did not find apparent methylation defects at other imprinted genome loci of the twins. WGS, SNP array, and Sanger sequencing did not detect the previously described genetic defects associated with familial PHP1B. Sanger sequencing also ruled out any novel genetic alterations in the entire NESP55/AS region. However, the analysis of 28 consecutive SNPs could not exclude the possibility of paternal heterodisomy in a span of 22 kb comprising exon NESP55 and AS exon 5.ConclusionOur comprehensive analysis of a pair of monozygotic twins with sporPHP1B ruled out all previously described genetic causes. Twin concordance indicates that the causative event was an imprinting error earlier than the timing of monozygotic twinning.

Supplemental material for: Sporadic Pseudohypoparathyroidism Type 1B in Monozygotic Twins: Insights into the Pathogenesis of Methylation Defects

Supplemental material for: Sporadic Pseudohypoparathyroidism Type 1B in Monozygotic Twins: Insights into the Pathogenesis of Methylation Defects

Pseudohypoparathyroidism-Ib due to novel heterozygous stop gain mutation in exon 8 of STX16 gene: A case report

We report a case of pseudohypoparathyroidism type 1b (PHP1b) manifesting in childhood with hypocalcemic seizures. Symptomatic hypocalcemia is a common emergency in the pediatric age group with vitamin D deficiency being a frequent underlying etiology and PHP is rare. Patients with PHP1b do not depict the Albright’s hereditary osteodystrophy (AHO) phenotype typical of patients with PHP1a and pseudopseudohypoparathyroidism (PPHP). The resistance to parathyroid hormone (PTH) is documented mostly at renal tubular site of action in patients with PHP1b. Hypothyroidism is reported occasionally, signifying resistance to thyroid-stimulating hormone (TSH). Individuals with autosomal dominant and maternally inherited form of PHP harbor methylation defects at GNAS exon A/B, while sporadic and non-familial cases harbor methylation defects at other locus sites, including differentially methylated regions (GNAS-DMR). A novel heterozygous stop gain mutation c.C910T/p.Arg304X in exon 8 of the STX16 gene (Syntaxin 16) was observed in our case. Resistance seems limited to the renal action of PTH alone as currently, TSH level is normal. Maternal STX16 gene analysis results confirmed the modality of inheritance.

Successful Management of Pseudohypoparathyroidism Type 1b in Pregnancy: A Case Report

Pseudohypoparathyroidism (PHP) refers to broad spectrum of genetic diseases characterized by peripheral resistance to Parathormone (PTH). This condition leads to hypocalcaemia, hyperphosphatemia and elevated PTH concentrations. There is scant literature on PHP in pregnancy with 9 cases published. The treatment of the disease in pregnant women is challenging and the main target is to avoid hyper/hypocalcemia to prevent maternal adverse effects and to protect fetal parathyroid glands development. We report a rare case of PHP type 1b in pregnant woman treated with a tailored therapy.

High-throughput Molecular Analysis of Pseudohypoparathyroidism 1b Patients Reveals Novel Genetic and Epigenetic Defects.

Patients with pseudohypoparathyroidism type 1b (PHP1b) show disordered imprinting of the maternal GNAS allele or paternal uniparental disomy (UPD). Genetic deletions in STX16 or in upstream exons of GNAS are present in many familial but not sporadic cases. Characterization of epigenetic and genetic defects in patients with PHP1b. DNA from 84 subjects, including 26 subjects with sporadic PHP1b, 27 affected subjects and 17 unaffected and/or obligate gene carriers from 12 PHP1b families, 11 healthy individuals, and 3 subjects with PHP1a was subjected to quantitative pyrosequencing of GNAS differentially methylated regions (DMRs), microarray analysis, and microsatellite haplotype analysis. Academic medical center. Molecular pathology of PHP1b. Healthy subjects, unaffected family members and obligate carriers of paternal PHP1b alleles, and subjects with PHP1a showed normal methylation of all DMRs. All PHP1b subjects showed loss of methylation (LOM) at the exon A/B DMR. Affected members of 9 PHP1b kindreds showed LOM only at the exon A/B DMR, which was associated with a 3-kb deletion of STX16 exons 4 through 6 in 7 families and a novel deletion of STX16 and adjacent NEPEPL1 in 1 family. A novel NESP deletion was found in 1 of 2 other families with more extensive methylation defects. One sporadic PHP1b had UPD of 20q, 2 had 3-kb STX16 deletions, and 5 had apparent epigenetic mosaicism. We found diverse patterns of defective methylation and identified novel or previously known mutations in 9 of 12 PHP1b families.

A Case of Pseudohypoparathyroidism Type 1b in Pregnancy

Introduction: Pseudohypoparathyroidism (PHP) type 1b is characterized by target organ resistance to PTH leading to hypocalcemia and hyperphosphatemia in the setting of elevated PTH due to abnormal imprinting that affects the regulatory elements of GNAS1. It poses challenges in management during pregnancy and lactation. We report the case of a patient who was diagnosed with PHP type 1b while pregnant. Case Presentation: A 30 year old woman, 16 weeks pregnant was referred for the evaluation of hypocalcemia. She had a history of traumatic fracture of her lower extremity and hypothyroidism treated with levothyroxine. She was noted to have hypocalcemia 1 year prior during routine labs. Family history was significant for hypothyroidism in her sister. On physical examination, she did not have phenotypic features of Albright hereditary osteodystrophy except for short stature. Before pregnancy her labs were significant for Ca 8.1 mg/dL(8.6–10.2), iCa 4.2 mg/dL(4.8–5.6), iPTH 289 pg/mL (14–64), creatinine 0.6 mg/dL(0.8–1.2), 25 vitamin D 22 ng/mL and 24 hr urine Ca 80 mg/24 hr (65-250mg). She was started on a combination of calcium citrate and carbonate 600 mg daily and vitamin D 1000 units daily. Labs while pregnant showed Ca 8.1 mg/dL, iCa 4.1 mg/dL, iPTH 184 pg/mL, PO4 4.9 mg/dL(2.5–3.5), 1,25 Vitamin D 53 pg/mL(18–72) and 25 Vitamin D 38 ng/mL. She had mild paresthesia and muscle cramps. Calcium supplements were increased to 1800 mg daily. While the urine Ca increased to 315 mg/24 hr, other biochemical parameters did not improve. Given her low Ca, high iPTH, high PO4, normal GFR and 25 vitamin D, PHP was suspected. Genetic testing showed loss of methylation at GNAS locus down to 5% (NL >43%) Diagnosis of PHP type 1b was made. Her Ca decreased the next months to a nadir of 7.9 mg/dL despite increased doses of calcium up to 1200 mg BID. Calcitriol 0.25 mcg BID was added. The rest of her pregnancy the serum Ca stayed between 8.1–8.6 mg/dL. She delivered a boy. At birth his Ca was 8.0 mg/ dL and PTH 81pg/mL. Genetic testing showed 41% methylation of GNAS. While breast feeding her Ca was 9.4 mg/dL, her calcitriol and calcium supplements were decreased. She continues to do well on calcium 630 mg daily and calcitriol 0.25 mcg daily with serum Ca between 8.5–8.8 mg/dL. Conclusion: The literature on PHP in pregnancy is scarce due to its rarity and the management is challenging due to altered calcium and vitamin D metabolism during pregnancy and lactation. The fetus draws calcium from maternal circulation and predisposes mother to hypocalcemia. Some patients may become normocalcemic during pregnancy due to placental secretion of 1,25 Vitamin D and PTHrp. There is also increased demand for calcium with lactation. There are genetic implications on the baby as it is inherited in an autosomal dominant mode. It is important to monitor calcium levels closely as there are multiple factors that could influence calcium metabolism in pregnancy.

Targeted Long-Read Sequencing Identifies a Retrotransposon Insertion as a Cause of Altered GNAS Exon A/B Methylation in a Family With Autosomal Dominant Pseudohypoparathyroidism Type 1b (PHP1B).

Pseudohypoparathyroidism type Ib (PHP1B) is characterized predominantly by resistance to parathyroid hormone (PTH) leading to hypocalcemia and hyperphosphatemia. These laboratory abnormalities are caused by maternal loss-of-methylation (LOM) at GNAS exon A/B, which reduces in cis expression of the stimulatory G protein α-subunit (Gsα). Paternal Gsα expression in proximal renal tubules is silenced through unknown mechanisms, hence LOM at exon A/B reduces further Gsα protein in this kidney portion, leading to PTH resistance. In a previously reported PHP1B family, affected members showed variable LOM at exon A/B, yet no genetic defect was found by whole-genome sequencing despite linkage to GNAS. Using targeted long-read sequencing (T-LRS), we discovered an approximately 2800-bp maternally inherited retrotransposon insertion nearly 1200 bp downstream of exon XL not found in public databases or in 13,675 DNA samples analyzed by short-read whole-genome sequencing. T-LRS data furthermore confirmed normal methylation at exons XL, AS, and NESP and showed that LOM comprising exon A/B is broader than previously thought. The retrotransposon most likely causes the observed epigenetic defect by impairing function of a maternally derived NESP transcript, consistent with findings in mice lacking full-length NESP mRNA and in PHP1B patients with deletion of exon NESP and adjacent intronic sequences. In addition to demonstrating that T-LRS is an effective strategy for identifying a small disease-causing variant that abolishes or severely reduces exon A/B methylation, our data demonstrate that this sequencing technology has major advantages for simultaneously identifying structural defects and altered methylation. © 2022 American Society for Bone and Mineral Research (ASBMR).

Familial Pseudohypoparathyroidism Type IB Associated with an SVA Retrotransposon Insertion in the GNAS Locus.

Loss of methylation (LOM) at GNAS-A/B:TSS-differentially methylated regions (DMRs) in the GNAS locus is observed in pseudohypoparathyroidism type 1B (PHP1B). Many PHP1B cases are sporadic, but autosomal dominant-PHP1B has a deletion involving NESP55 expressed from the maternal allele or STX16 located upstream of the GNAS locus on the maternal allele. We report the possible first familial PHP1B cases with retrotransposon insertion in the GNAS locus on the maternal allele. To our knowledge, they are the possible first cases with imprinting disorders caused by retrotransposon insertion. The two sibling cases experienced tetany and/or cramps from school age and had hypocalcemia and an increased serum intact parathyroid hormone (PTH) level together with overweight, round face, and normal intellectual levels. Methylation analysis for DMRs in the GNAS locus showed only LOM of the GNAS-A/B:TSS-DMR. Copy number abnormalities at STX16 and the GNAS locus were not detected by array comparative genomic hybridization. Whole-genome sequencing and Sanger sequencing revealed an approximately 1000-bp SVA retrotransposon insertion upstream of the first exon of A/B on the GNAS locus in these siblings. Whole-genome methylome analysis by Enzymatic Methyl-Seq in the siblings showed normal methylation status in the region surrounding the insertion site and mild LOM of the GNAS-A/B:TSS-DMR. We conducted transcriptome analysis using mRNA from skin fibroblasts and induced pluripotent stem cells (iPSCs) derived from the siblings and detected no aberrant NESP55 transcripts. Quantitative reverse-transcriptase PCR (qRT-PCR) analysis in skin fibroblasts showed increased A/B expression in the patients and no NESP55 expression, even in a control. qRT-PCR analysis in iPSCs showed decreased NESP55 expression with normal methylation status of the GNAS-NESP:TSS-DMR in the patients. The retrotransposon insertion in the siblings likely caused decreased NESP55 expression that could lead to increased A/B expression via LOM of the GNAS-A/B:TSS-DMR, subsequent reduced Gsα expression, and finally, PHP1B development. © 2022 American Society for Bone and Mineral Research (ASBMR).

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.

Clinical and gene methylation analysis of type 1b pseudohypoparathyroidism

Objective This study was carried out to analyze the clinical characteristics of pseudohypopara-thyroidism(PHP) type 1b, and to improve the understanding and diagnosis of the disease. Methods Five patients with molecular diagnosis of pseudohypoparathyroidism type 1b in our hospital during 2018 were enrolled, their clinical data, biochemical indicators, imaging, and gene detection results were analyzed. Results There were 4 females and 1 male, with low calcium, high phosphorus and high PTH serum concentrations. The onset age span was large and the onset symptoms were different. Family history may not be obvious. There was abnormal methylation of GNAS gene or deletion of exon STX16 in methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) detection while gene sequencing result was negative. Conclusion MS-MLPA detection was still needed in patients with suspected PHP but negative gene sequencing result. Different methylation abnormalities and copy number variations might be correlated with the onset symptoms and familial of type 1b PHP. Key words: Pseudohypoparathyroidism, type 1b; GNAS; Methylation