The Second Activating Glucokinase Mutation (A456V)
Implications for Glucose Homeostasis and Diabetes Therapy
- Henrik B.T. Christesen1,
- Bendt B. Jacobsen1,
- Stella Odili2,
- Carol Buettger2,
- Antonio Cuesta-Munoz2,
- Torben Hansen3,
- Klaus Brusgaard4,
- Ornella Massa5,
- Mark A. Magnuson6,
- Chiyo Shiota6,
- Franz M. Matschinsky2 and
- Fabrizio Barbetti57
- 1Department of Pediatrics, Odense University Hospital, Odense, Denmark
- 2Department of Biochemistry and Biophysics and Diabetes Research Center, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- 3Steno Diabetes Center, Gentofte, Denmark
- 4Department of Clinical Biochemistry and Genetics, Odense University Hospital, Odense, Denmark
- 5IBCIT Biomedical Scientific Park S Raffaele, Rome, Italy
- 6Department of Molecular Biophysics and Physiology, Vanderbilt University School of Medicine, Nashville, Tennessee
- 7Bambino Gesù Pediatric Hospital, Rome, Italy
Abstract
In this study, a second case of hyperinsulinemic hypoglycemia due to activation of glucokinase is reported. The 14-year-old proband had a history of neonatal hypoglycemia, treated with diazoxide. He was admitted with coma and convulsions due to nonketotic hypoglycemia. His BMI was 34 kg/m2, and his fasting blood glucose ranged from 2.1 to 2.7 mmol/l, associated with inappropriately high serum levels of insulin, C-peptide, and proinsulin. An oral glucose tolerance test (OGTT) showed exaggerated responses of these peptides followed by profound hypoglycemia. Treatment with diazoxide and chlorothiazide was effective. His mother never had clinical hypoglycemic symptoms, even though her fasting blood glucose ranged from 2.9 to 3.5 mmol/l. Increases in serum insulin, C-peptide, and proinsulin in response to an OGTT suggested a lower threshold for glucose-stimulated insulin release (GSIR). Screening for mutations in candidate genes revealed a heterozygous glucokinase mutation in exon 10, substituting valine for alanine at codon 456 (A456V) in the proband and his mother. The purified recombinant glutathionyl S-transferase fusion protein of the A456V glucokinase revealed a decreased glucose S0.5 (the concentration of glucose needed to achieve the half-maximal rate of phosphorylation) from 8.04 (wild-type) to 2.53 mmol/l. The mutant’s Hill coefficient was decreased, and its maximal specific activity kcat was increased. Mathematical modeling predicted a markedly lowered GSIR threshold of 1.5 mmol/l. The theoretical and practical implications are manifold and significant.
Footnotes
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Address correspondence and reprint requests to Henrik B.T. Christesen, Department of Pediatrics, Odense University Hospital, 5000 Odense C, Denmark. E-mail: thybo{at}dadlnet.dk.
Received for publication 20 August 2001 and accepted in revised form 17 December 2001.
CT, computed tomography; DGGE, denaturing gradient gel electrophoresis; EEG, electroencephalogram; GDH, glutamate dehydrogenase; GK, glucokinase; GSIR, glucose-stimulated insulin release; GST, glutathionyl S-transferase; MODY, maturity-onset diabetes of the young; OGTT, oral glucose tolerance test; PHHI, persistent hyperinsulinemic hypoglycemia in infancy; PND, permanent neonatal diabetes; S0.5, the concentration of glucose needed to achieve the half-maximal rate of phosphorylation; SSCP, single-strand conformation polymorphism.
- DIABETES
