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      Challenges in diagnosis and management of neonatal hyperparathyroidism in a resource-limited country: a case series from a Sudanese family

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          Abstract

          Neonatal hyperparathyroidism is a rare disease caused by a homozygous inactivating mutation in the calcium sensing receptor gene. It presents early in life with life threatening manifestations of hypercalcemia, if left untreated the condition may be lethal. This is the first case series reported from Sudan. Three Sudanese siblings presented with severe symptoms of hypercalcemia in the form of polyuria, failure to thrive and multiple bone fractures. Serum calcium and parathyroid hormone levels were very high with low phosphate and normal alkaline phosphatase levels. Ultrasonography and sestamibi scan were normal and did not assist in diagnosing their condition. Medical management was a great challenge due to unavailability of medications such as parentral bisphosphonates and calcimimetics. Parathyroidectomy was inevitable. Tissue biopsies revealed parathyroid hyperplasia and no adenoma. Gene sequencing revealed a homozygous missense mutation: c 2038 C T p (Arg680Cys) in two siblings, both parents were heterozygous for the same missense mutation. Our report reflects the challenges in diagnosis and management of neonatal hyperparathyroidism in resource limited countries. We also highlight the importance of genetic testing in the diagnosis and management of such cases in countries with high rates of consanguineous marriage.

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          Most cited references20

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          Urinary phosphate/creatinine, calcium/creatinine, and magnesium/creatinine ratios in a healthy pediatric population.

          To determine reference values for urinary phosphate/creatinine (Cr) concentration ratios and to complete reference values for urinary calcium/creatinine and magnesium/creatinine ratios in the second morning urine sample of healthy infants, children, and adolescents. Urinary P/Cr, Ca/Cr, and Mg/Cr ratios were determined from the second morning urine sample. Two urine samples were obtained 1 week apart from most subjects to assess reproducibility. Kindergartens and schools of Lausanne, Switzerland. A total of 410 healthy children aged 1 month to 17 years (197 girls and 213 boys) participated in the study. The 5th and 95th percentiles were estimated from 664 urine samples. There were no differences related to sex. A nonlinear regression in terms of age was used to smooth the estimated percentiles yielding reference curves from which critical values may be obtained for any given age. The 95th percentile for urinary Ca/Cr and Mg/Cr agreed with previously reported values in children older than 7 years. The upper limit of the three solute/creatinine ratios decreased significantly with age: for urinary P/Cr from 19.0 mol/mol at 1 month to 2.7 at 14 years; for urinary Ca/Cr from 2.2 to 0.7 mol/mol, and for urinary Mg/Cr from 2.2 to 0.6 mol/mol. Lower limits varied little. Interindividual and intraindividual variations decreased with age. Urinary P/Cr, Ca/Cr, and Mg/Cr ratios vary strongly with age. We provide reference values, expressed both in SI and in mass units, for urinary P/Cr, Ca/Cr, and Mg/Cr in children aged one month to 17 years.
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            Familial hypocalciuric hypercalcemia and neonatal severe hyperparathyroidism. Effects of mutant gene dosage on phenotype.

            Neonatal severe hyperparathyroidism is a rare life-threatening disorder characterized by very high serum calcium concentrations (> 15 mg/dl). Many cases have occurred in families with familial hypocalciuric hypercalcemia, a benign condition transmitted as a dominant trait. Among several hypothesized relationships between the two syndromes is the suggestion that neonatal severe hyperparathyroidism is the homozygous form of familial hypocalciuric hypercalcemia. To test this hypothesis, we refined the map location of the gene responsible for familial hypocalciuric hypercalcemia on chromosome 3q. Analyses in 11 families defined marker loci closely linked to the gene responsible for familial hypocalciuric hypercalcemia. These loci were then analyzed in four families with parental consanguinity and offspring with neonatal severe hyperparathyroidism. Each individual who was homozygous for loci that are closely linked to the gene responsible for familial hypocalciuric hypercalcemia had neonatal severe hyperparathyroidism. The calculated odds of linkage between these disorders of > 350,000:1 (lod score = 5.56). We conclude that dosage of the gene defect accounts for these widely disparate clinical phenotypes; a single defective allele causes familial hypocalciuric hypercalcemia, while two defective alleles causes neonatal severe hyperparathyroidism.
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              Rescue of calcium-sensing receptor mutants by allosteric modulators reveals a conformational checkpoint in receptor biogenesis.

              The calcium-sensing receptor (CaR), a member of G protein-coupled receptor family C, regulates systemic calcium homeostasis by activating G(q)- and G(i)-linked signaling in the parathyroid, kidney, and intestine. CaR is ubiquitinated by the E3 ligase dorfin and degraded via the endoplasmic reticulum-associated degradation pathway (Huang, Y., Niwa, J., Sobue, G., and Breitwieser, G. E. (2006) J. Biol. Chem. 281, 11610-11617). Here we provide evidence for a conformational or functional checkpoint in CaR biogenesis using two complementary approaches. First we characterized the sensitivity of loss- or gain-of-function CaR mutants to proteasome inhibition by MG132. The stabilization of loss-of-function mutants and insensitivity of gain-of-function mutants to MG132 suggests that receptor sensitivity to calcium influences susceptibility to proteasomal degradation. Second, we used the allosteric activator NPS R-568 and antagonist NPS 2143 to promote the active and inactive conformations of wild type CaR, respectively. Overnight culture in NPS R-568 increased expression of CaR, whereas NPS 2143 had the opposite effect. NPS R-568 and NPS 2143 differentially regulated maturation and cell surface expression of wild type CaR, directly affecting maximal signaling responses. NPS R-568 rescued expression of loss-of-function CaR mutants, increasing plasma membrane expression and ERK1/2 phosphorylation in response to 5 mM Ca(2+). Disorders of calcium homeostasis caused by CaR mutations may therefore result from altered receptor biogenesis independent of receptor function, i.e. a protein folding disorder. The allosteric modulators NPS R-568 and NPS 2143 not only alter CaR sensitivity to calcium and hence signaling but also modulate receptor expression.
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                Author and article information

                Contributors
                Journal
                Pan Afr Med J
                Pan Afr Med J
                PAMJ
                The Pan African Medical Journal
                The African Field Epidemiology Network
                1937-8688
                15 October 2021
                2021
                : 40
                : 105
                Affiliations
                [1 ]Department of Pediatric Endocrinology, Gaafar Ibn Auf Pediatric Tertiary Hospital, Khartoum, Sudan,
                [2 ]Radbound University Medical Center, Nijmegen, Netherlands,
                [3 ]Sudan Childhood Diabetes Center, Khartoum, Sudan,
                [4 ]Faculty of Medicine, University of Khartoum, Khartoum, Sudan
                Author notes
                Corresponding author: Samar Sabir Hassan, Department of Pediatric Endocrinology, Gaafar Ibn Auf Pediatric Tertiary Hospital, Khartoum, Sudan. dr.samar.hassan.80@ 123456gmail.com
                Article
                PAMJ-40-105
                10.11604/pamj.2021.40.105.29527
                8627147
                34887979
                45f2a244-6b9e-4075-a8dc-e0f9aeb3dbd0
                Copyright: Samar Sabir Hassan et al.

                The Pan African Medical Journal (ISSN: 1937-8688). This is an Open Access article distributed under the terms of the Creative Commons Attribution International 4.0 License ( https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 26 April 2021
                : 14 August 2021
                Categories
                Case Series

                Medicine
                neonatal hyperparathyroidism,calcium sensing receptor,parathyroidectomy,hypercalcemia
                Medicine
                neonatal hyperparathyroidism, calcium sensing receptor, parathyroidectomy, hypercalcemia

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