The second activating glucokinase mutation (A456V): implications for glucose homeostasis and diabetes therapy.
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/m(2), 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 S(0.5) (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 k(cat) was increased. Mathematical modeling predicted a markedly lowered GSIR threshold of 1.5 mmol/l. The theoretical and practical implications are manifold and significant.
Christesen
Henrik B T
HB
Department of Pediatrics, Odense University Hospital, Odense, Denmark. thybo@dadlnet.dk
Jacobsen
Bendt B
BB
Odili
Stella
S
Buettger
Carol
C
Cuesta-Munoz
Antonio
A
Hansen
Torben
T
Brusgaard
Klaus
K
Massa
Ornella
O
Magnuson
Mark A
MA
Shiota
Chiyo
C
Matschinsky
Franz M
FM
Barbetti
Fabrizio
F
D000293:Adolescent; D000494:Allosteric Regulation; D003920:Diabetes Mellitus / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism; D003981:Diazoxide / Q000627:therapeutic use; D004789:Enzyme Activation; D005941:Glucokinase / Q000235:genetics*; D005947:Glucose / Q000378:metabolism*; D005982:Glutathione Transferase / Q000235:genetics; D006706:Homeostasis; D006801:Humans; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age; D007328:Insulin / Q000097:blood / Q000378:metabolism; D000078790:Insulin Secretion; D007700:Kinetics; D008297:Male; D020125:Mutation, Missense; D010766:Phosphorylation
D007328:Insulin; D005982:Glutathione Transferase; D005941:Glucokinase; D005947:Glucose; D003981:Diazoxide