Case Report: Hypoglycemia Due to a Novel Activating Glucokinase Variant in an Adult – a Molecular Approach

Anojian Koneshamoorthy, Dilan Seniveratne-Epa, Genevieve Calder, Matthew Sawyer, Thomas W.H. Kay, Stephen Farrell, Thomas Loudovaris, Lina Mariana, Davis McCarthy, Ruqian Lyu, Xin Liu, Peter Thorn, Jason Tong, Lit Kim Chin, Margaret Zacharin, Alison Trainer, Shelby Taylor, Richard J. MacIsaac, Nirupa Sachithanandan, Helen E. ThomasBalasubramanian Krishnamurthy

Research output: Contribution to journalArticlepeer-review

Abstract

We present a case of an obese 22-year-old man with activating GCK variant who had neonatal hypoglycemia, re-emerging with hypoglycemia later in life. We investigated him for asymptomatic hypoglycemia with a family history of hypoglycemia. Genetic testing yielded a novel GCK missense class 3 variant that was subsequently found in his mother, sister and nephew and reclassified as a class 4 likely pathogenic variant. Glucokinase enables phosphorylation of glucose, the rate-limiting step of glycolysis in the liver and pancreatic β cells. It plays a crucial role in the regulation of insulin secretion. Inactivating variants in GCK cause hyperglycemia and activating variants cause hypoglycemia. Spleen-preserving distal pancreatectomy revealed diffuse hyperplastic islets, nuclear pleomorphism and periductular islets. Glucose stimulated insulin secretion revealed increased insulin secretion in response to glucose. Cytoplasmic calcium, which triggers exocytosis of insulin-containing granules, revealed normal basal but increased glucose-stimulated level. Unbiased gene expression analysis using 10X single cell sequencing revealed upregulated INS and CKB genes and downregulated DLK1 and NPY genes in β-cells. Further studies are required to see if alteration in expression of these genes plays a role in the metabolic and histological phenotype associated with glucokinase pathogenic variant. There were more large islets in the patient’s pancreas than in control subjects but there was no difference in the proportion of β cells in the islets. His hypoglycemia was persistent after pancreatectomy, was refractory to diazoxide and improved with pasireotide. This case highlights the variable phenotype of GCK mutations. In-depth molecular analyses in the islets have revealed possible mechanisms for hyperplastic islets and insulin hypersecretion.

Original languageEnglish (US)
Article number842937
JournalFrontiers in Endocrinology
Volume13
DOIs
StatePublished - Mar 17 2022

Keywords

  • MODY
  • congenital hyperinsulinism
  • glucokinase
  • hyperplastic islets
  • hypoglycemia

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism

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