A case of a hemodialysis patient with secondary hyperparathyroidism who was resistant to etelcalcetide treatment but not to cinacalcet hydrochloride

Although both cinacalcet and etelcalcetide are calcimimetics that directly inhibit parathyroid hormone (PTH) secretion by activating the calcium (Ca)-sensing receptor (CaSR), their binding sites are different. We report a first case of a hemodialysis (HD) patient with secondary hyperparathyroidism (SHPT), in whom cinacalcet, but not etelcalcetide, could reduce serum intact PTH (i-PTH) levels. A HD patient received total parathyroidectomy (PTx) with auto-transplantation 16 years earlier. Due to SHPT relapse, cinacalcet was started at 7 years after PTx. His i-PTH levels had been controlled with both 75–100 mg of cinacalcet and 4.5 μg/week of calcitriol for a year before switching from cinacalcet to etelcalcetide. At 1 month following the switch, his serum i-PTH level increased to 716 pg/mL. The dose of etelcalcetide was gradually increased and finally reached the maximal dose of 45 mg/week. Because even the maximal dose of etelcalcetide for > 4 months did not reduce his serum i-PTH levels to < 700 pg/mL, etelcalcetide was switched to 50 mg/day of cinacalcet, which reduced the levels to 208 pg/mL at 2 months after the switch. Genomic sequencing test using whole blood revealed no mutation in the portion including Cys 482 of CaSR gene. The patient was resistant to etelcalcetide treatment but not to cinacalcet, suggesting the possibility that the enlarged parathyroid gland has some change in the portion including Cys 482 in the CaSR gene. Therefore, considering the possibility of etelcalcetide resistance during SHPT treatment should be kept in mind.

Polymorphisms Contributing to Calcium Status: A Systematic Review

This systematic review assessed genotypes and changes in calcium homeostasis. A literature search was performed in EMBASE, Medline and CENTRAL on 7 August 2020 identifying 1012 references. Studies were included with any human population related to the topic of interest, and genetic variations in genes related to calcium metabolism were considered. Two reviewers independently screened references, extracted relevant data and assessed study quality using the Q-Genie tool. Forty-one studies investigating Single Nucleotide Polymorphisms (SNPs) in relation to calcium status were identified. Almost half of the included studies were of good study quality according to the Q-Genie tool. Seventeen studies were cross-sectional, 14 case-control, seven association and three were Mendelian randomization studies. Included studies were conducted in over 18 countries. Participants were mainly adults, while six studies included children and adolescents. Ethnicity was described in 31 studies and half of these included Caucasian participants. Twenty-six independent studies examined the association between calcium and polymorphism in the calcium-sensing receptor (CASR) gene. Five studies assessed the association between polymorphisms of the Vitamin D receptor (VDR) gene and changes in calcium levels or renal excretion. The remaining ten studies investigated calcium homeostasis and other gene polymorphisms such as the CYP24A1 SNP or CLDN14. This study identified several CASR, VDR and other gene SNPs associated with calcium status. However, to provide evidence to guide dietary recommendations, further research is needed to explore the association between common polymorphisms and calcium requirements.

The bromodomain inhibitor JQ1+ reduces calcium-sensing receptor activity in pituitary cell-lines

Corticotrophinomas represent 10% of all surgically removed pituitary adenomas, however, current treatment options are often not effective and there is a need for improved pharmacological treatments. Recently, JQ1+, a bromodomain inhibitor that promotes gene transcription by binding acetylated histone residues and recruiting transcriptional machinery, has been shown to reduce proliferation in a murine corticotroph cell-line, AtT20. RNA-Seq analysis of AtT20 cells following treatment with JQ1+ identified the calcium-sensing receptor (CaSR) gene as significantly downregulated, which was subsequently confirmed using real-time PCR and western blot analysis. CaSR is a G protein-coupled receptor that plays a central role in calcium homeostasis but can elicit non-calcitropic effects in multiple tissues, including the anterior pituitary where it helps regulate hormone secretion. However, in AtT20 cells, CaSR activates a tumour-specific cAMP pathway that promotes ACTH and PTHrP hypersecretion. We hypothesised that the Casr promoter may harbour binding sites for BET proteins, and using chromatin immunoprecipitation (ChIP)-sequencing demonstrated that the BET protein Brd3 binds to the promoter of the Casr gene. Assessment of CaSR signalling showed that JQ1+ significantly reduced Ca2+e-mediated increases in intracellular calcium (Ca2+i) mobilisation and cAMP signalling. However, the CaSR negative allosteric modulator, NPS-2143, was unable to reduce AtT20 cell proliferation, indicating that reducing CaSR expression rather than activity is likely required to reduce pituitary cell proliferation. Thus, these studies demonstrate that reducing CaSR expression may be a viable option in the treatment of pituitary tumours. Moreover, current strategies to reduce CaSR activity, rather than protein expression for cancer treatments, may be ineffective.

Whole-Exome Sequencing for Identification of Genetic Variants Involved in Vitamin D Metabolic Pathways in Families With Vitamin D Deficiency in Saudi Arabia

BackgroundNumerous research studies have found an association between vitamin D (vitD) status and single-nucleotide polymorphisms (SNPs) in genes involved in vitD metabolism. It is notable that the influence of these SNPs on 25-hydroxyvitamin D [25(OH)D] levels might vary in different populations. In this study, we aimed to explore for genetic variants in genes related to vitD metabolism in families with vitD deficiency in Saudi Arabia using whole-exome sequencing (WES).MethodsThis family-based WES study was conducted for 21 families with vitD deficiency (n = 39) in Saudi Arabia. WES was performed for DNA samples, then resulting WES data was filtered and a number of variants were prioritized and validated by Sanger DNA sequencing.ResultsSeveral missense variants in vitD-related genes were detected in families. We determined two variants in low-density lipoprotein 2 gene (LRP2) with one variant (rs2075252) observed in six individuals, while the other LRP2 variant (rs4667591) was detected in 13 subjects. Single variants in 7-dehydrocholesterol reductase (DHCR7) (rs143587828) and melanocortin-1 receptor (MC1R) (rs1805005) genes were observed in two subjects from two different families. Other variants in group-specific component (GC), cubilin (CUBN), and calcium-sensing receptor (CASR) gene were found in index cases and controls. Polymorphisms in GC (rs9016) and CASR (rs1801726) were found in the majority of family cases (94 and 88%), respectively.ConclusionIn vitD-deficient families in Saudi Arabia, we were able to detect a number of missense exonic variants including variants in GC (rs9016), CUBN (rs1801222), CASR (rs1801726), and LRP2 (rs4667591). However, the existence of these variants was not different between affected family members and non-affected controls. Additionally, we were able to find a mutation in DHCR7 (rs143587828) and a polymorphism in LRP2 (rs2075252), which may affect vitD levels and influence vitD status. Further studies are now required to confirm the association of these variants with vitD deficiency.

PREVALENCE OF SPINK 1 AND CASR GENE MUTATIONS IN ACUTE AND RECURRENT ACUTE PANCREATITIS : A STUDY FROM CENTRAL INDIA

Background: Genetic factors may play an important role in the pathogenesis of acute pancreatitis. It has been observed in various studies that the presence of risk factors alone like alcohol abuse or gall bladder stones does not lead to attacks of pancreatitis in all the patients. This leads to assumption that genetic factors may decrease the threshold for the development of pancreatitis in presence of one or more risk factors. We observed that there is a paucity of data regarding the role of genetics in acute pancreatitis (AP) and recurrent acute pancreatitis (RAP) in our part of the world and we aimed at studying the prevalence of genetic mutations in such patients. Methods: Our study intended to nd the prevalence of SPINK1 N34S (Serine protease inhibitor kazal type 1) and CaSR (Calcium sensing receptor) gene mutations in patients of AP and RAP. A total of 50 patients and 25 age and gender matched controls entered our study. Blood samples were obtained from all the cases and controls for routine investigations and genetic analysis. SPINK 1 N34S and CaSR gene mutation studies were done in all the patients and controls. Results: Alcohol (64%) followed by gallbladder stone disease (20%) was the most common aetiology of pancreatitis. SPINK 1 N34S mutation was present in 21 patients and 2 controls whereas CaSR gene mutation was present in 13 patients and 2 controls. Patients with SPINK 1 N34S and CaSR gene mutations were younger than the patients without these mutations. Prevalence of both SPINK1 N34S and CaSR gene mutations was higher in patients of RAP than AP. These mutations were not associated with aetiology or severity of pancreatitis. Conclusion: The prevalence SPINK 1 N34S and CaSR gene mutations was higher in patients of AP and RAP. Identication of these mutations in patients of AP can help in the identication of patients who are at increased risk of recurrent attacks of AP

A Novel Variant in the CASR Gene c.368T>Cp.(Leu123Ser) in a Case of Hypocalcemia Refractory to Standard Medical Therapy

Introduction: Hypoparathyroidism is characterized by low or inappropriately normal PTH production, hypocalcemia and hyperphosphatemia. Autosomal dominant hypocalcemia (ADH) type 1 is one of the genetic etiologies of this, caused by heterozygous activating mutations in the CASR gene. Some individuals fail to meet treatment goals despite standard therapy. Clinical Case: A 13-year-old male patient was admitted in the emergency department due to syncope during physical activity. There was no reference to seizures or other complaints. Standard screening for metabolic diseases revealed no changes at the 7th day of life and family history was unremarkable. There was a history of febrile seizures up to 5 years of age with several hospitalizations for diagnosis investigation that were inconclusive. Physical examination showed a positive Chvostek signal, without other changes. A basic workup revealed hypocalcemia 1.67mmol/L (NR: 2.19-2.66), hyperphosphatemia 3.06mmol/L (NR: 0.95-1.75), hypomagnesemia 0.62mmol/L (NR: 0.7-1.0), low 25Hydroxyvitamin D 8.7ng/mL (NR: &gt;30ng/mL) and inappropriately low PTH 4.0pg/mL (NR: 16.0-87.0). Cranial computed tomography scan showed bilateral calcifications of the basal ganglia. Dual-energy x-ray absorptiometry revealed bone mineral density z-scores increased 15% in spine lumbar and decreased 7% in left femur. Cardiac ultrasound and electrocardiography were normal. The patient started therapy with intravenous calcium gluconate. During this treatment, he developed significant calcification of the peripheral veins at the site of administration, leading to intravenous therapy suspension. The dose of oral calcium, calcitriol and magnesium was gradually increased and sevelamer started to control hyperphosphatemia. Despite the optimization, the patient maintained hypocalcemia refractory to standard therapy. As a last resource strategy in therapeutic optimization, the patient started on rhPTH (1-34). Ever since, the patient has been clinically asymptomatic with biochemical stability and with a reasonable quality of life. At age 18, renal ultrasound revealed diffuse medullary nephrocalcinosis. The genetic testing revealed a novel variant c.368T&gt;C p.(Leu123Ser) likely pathogenic in heterozygosity in the CASR gene, suggesting the diagnosis of ADH type 1. The patient′s mother did not give her consent for genetic study and patient’s father had already died with a diagnosis of acute leukemia. Conclusion: This case can be explained by the presence of a likely pathogenic variant in heterozygosity in the CASR gene that has been described in the medical literature that has not been identified in gnomAD population database, suggesting the diagnosis of ADH type 1. rhPTH (1-34) may be a treatment option for those individuals who are not well controlled on standard therapy, but long-term follow-up studies are needed to reinforce its safety.

Atypical Presentation of Familial Hypocalciuric Hypercalcemia: Case Report

Background: Differentiation between familial hypocalciuric hypercalcemia (FHH) and primary hyperparathyroidism (PHPT) can be challenging in certain cases in the absence of DNA analysis of the calcium sensing receptor gene. The distinction between those two clinical entities with overlapping biochemical features therefore relies on the calcium to creatinine clearance ratio (CCCR), which is expected to be low in FHH (&lt;0.01 in 80% of cases and between 0.01 and 0.02 in approximately 20% of patients)1. Patients with PHPT usually have a CCCR of&gt;= 0.02. A lower CCCR between 0.01 and 0.02 can be seen in approximately 20% of patients1,2and is more commonly seen in the presence of vitamin D insufficiency, impaired renal function, low calcium intake or being of African descent. It is advised to stop drugs which can contribute to hypercalcemia and lower the CCCR such as thiazide diuretics prior to evaluating the CCCR. Clinical Case: A 56-year-old lady was referred for evaluation of persistent hypercalcemia post parathyroidectomy and fatigue. She had mildly elevated ionized serum calcium (iCa) and a mid-normal PTH with a CCCR of 0.024. She had a normal BMD with no prior fragility fractures and passed a kidney stone prior to her presentation. Physical exam was unremarkable. She had previously travelled to Tampa and had a subtotal parathyroidectomy 3 glands (RU, LU, RL) for a possible diagnosis of PHPT, tissue biopsy showed hyperplastic parathyroids. Her MEN1 gene analysis was negative for MEN1 mutation and MRI of the abdomen was unremarkable. Her mother had a diagnosis of PHPT and osteoporosis. The iCa remained mildly elevated at 1.43 mmol/L (1.15–1.3) with a 24 hr urinary CCCR at 0.024 and a mid-normal PTH of 4.4 pmol/L (1.6–6.9). Her eGFR was 104 mls/min, 25 vitamin D 82 nmol/L (75–250), 1,25 dihydroxy vitamin D 122 pmol/L (60–206), PO4 0.90 mmol/L (0.8–1.45) and alkaline phosphatase 46 U/L (35–120) were all normal. She continued to have mild symptoms of hypercalcemia and her bone scan was negative for underlying skeletal pathology. DNA studies for mutations in the CaSR gene were completed. This confirmed the presence of a heterozygous loss of function mutation in the CASR gene at c493-2A&gt;G which appears to be pathogenic. Conclusion: The CCCR is useful in differentiating PHPT from FHH however in certain cases of FHH the CCCR may be higher then expected and we have now confirmed the presence of FHH with a molecular diagnosis in a patient with a CCCR as high as 0.02. References: 1 Gunn, IR, Gaffney, D. Clinical and laboratory features of calcium-sensing receptor disorders: a systematic review. Ann Clin Biochem 2004; 41:441–58 2 Stephen J. Marx, Letter to the Editor: Distinguishing Typical Primary Hyperparathyroidism From Familial Hypocalciuric Hypercalcemia by Using an Index of Urinary Calcium, The Journal of Clinical Endocrinology & Metabolism, 2015