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Maria Cabrer Endocrine Unit, Hospital Comarcal d’Inca, Inca, Spain

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Guillermo Serra Endocrine Unit, Hospital Universitari Son Espases, Palma, Spain

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María Soledad Gogorza Endocrine Unit, Hospital Universitari Son Espases, Palma, Spain

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Vicente Pereg Endocrine Unit, Hospital Universitari Son Espases, Palma, Spain

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Summary

Chromosome 22q11.2 deletion syndrome (22q11.2DS) is a genetic syndrome that may present with hypocalcemia due to primary hypoparathyroidism (PH) at any age. We report a new diagnosis of 22q11.2DS in a 57-year-old man who presented with symptomatic hypocalcemia. It is important to consider genetic causes of hypocalcemia due to PH regardless of age.

Learning points:

  • It is important to discard genetic cause of primary hypoparathyroidism in a patient without autoimmune disease or prior neck surgery.

  • A new diagnosis of a hereditary disease has familial implications and needs genetic counselling.

  • It is also important to discard other syndrome’s comorbidities.

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Etienne Larger Department of Diabetology, Hôpital Bichat and University Paris Denis Diderot, Paris, France

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Nicolai J Wewer Albrechtsen Department of Biomedical Sciences
Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark

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Lars H Hansen Department of Molecular Signaling, Hagedorn Research Institute, Gentofte, Denmark

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Richard W Gelling Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore

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Jacqueline Capeau Inserm UMR_S 938, Centre de Recherche Saint-Antoine, Paris, France
Sorbonne University, UPMC, University of Paris 6, Institute of Cardiometabolism and Nutrition (ICAN), Paris, France

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Carolyn F Deacon Department of Biomedical Sciences
Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark

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Ole D Madsen Global Research External Affairs, Novo Nordisk A/S, 2760 Måløv, Denmark

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Fumiatsu Yakushiji Department of Internal Medicine, Tokyo Metropolitan Bokutoh Hospital, Tokyo, Japan
Department of Education Planning and Development, Faculty of Medicine, Toho University, Tokyo, Japan

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Pierre De Meyts Global Research External Affairs, Novo Nordisk A/S, 2760 Måløv, Denmark

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Jens J Holst Department of Biomedical Sciences
Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark

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Erica Nishimura Metabolic Disease Research, Novo Nordisk A/S, Måløv, Denmark

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Summary

Glucagon stimulates hepatic glucose production by activating specific glucagon receptors in the liver, which in turn increase hepatic glycogenolysis as well as gluconeogenesis and ureagenesis from amino acids. Conversely, glucagon secretion is regulated by concentrations of glucose and amino acids. Disruption of glucagon signaling in rodents results in grossly elevated circulating glucagon levels but no hypoglycemia. Here, we describe a patient carrying a homozygous G to A substitution in the invariant AG dinucleotide found in a 3′ mRNA splice junction of the glucagon receptor gene. Loss of the splice site acceptor consensus sequence results in the deletion of 70 nucleotides encoded by exon 9, which introduces a frame shift and an early termination signal in the receptor mRNA sequence. The mutated receptor neither bound 125I-labeled glucagon nor induced cAMP production upon stimulation with up to 1 µM glucagon. Despite the mutation, the only obvious pathophysiological trait was hyperglucagonemia, hyperaminoacidemia and massive hyperplasia of the pancreatic α-cells assessed by histology. Our case supports the notion of a hepato–pancreatic feedback system, which upon disruption leads to hyperglucagonemia and α-cell hyperplasia, as well as elevated plasma amino acid levels. Together with the glucagon-induced hypoaminoacidemia in glucagonoma patients, our case supports recent suggestions that amino acids may provide the feedback link between the liver and the pancreatic α-cells.

Learning points:

  • Loss of function of the glucagon receptor may not necessarily lead to the dysregulation of glucose homeostasis.

  • Loss of function of the glucagon receptor causes hyperaminoacidemia, hyperglucagonemia and α-cell hyperplasia and sometimes other pancreatic abnormalities.

  • A hepato–pancreatic feedback regulation of the α-cells, possibly involving amino acids, may exist in humans.

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