title: Additive effects of genetic variation in GCK and G6PC2 on insulin secretion and fasting glucose.
abstract: OBJECTIVE
  Glucokinase (GCK) and glucose-6-phosphatase catalytic subunit 2 (G6PC2) regulate the glucose-cycling step in pancreatic beta-cells and may regulate insulin secretion. GCK rs1799884 and G6PC2 rs560887 have been independently associated with fasting glucose, but their interaction on glucose-insulin relationships is not well characterized.
  
  
  METHODS
  We tested whether these variants are associated with diabetes-related quantitative traits in Mexican Americans from the BetaGene Study and attempted to replicate our findings in Finnish men from the METabolic Syndrome in Men (METSIM) Study.
  
  
  RESULTS
  rs1799884 was not associated with any quantitative trait (corrected P > 0.1), whereas rs560887 was significantly associated with the oral glucose tolerance test 30-min incremental insulin response (30' Deltainsulin, corrected P = 0.021). We found no association between quantitative traits and the multiplicative interaction between rs1799884 and rs560887 (P > 0.26). However, the additive effect of these single nucleotide polymorphisms was associated with fasting glucose (corrected P = 0.03) and 30' Deltainsulin (corrected P = 0.027). This additive association was replicated in METSIM (fasting glucose, P = 3.5 x 10(-10) 30' Deltainsulin, P = 0.028). When we examined the relationship between fasting glucose and 30' Deltainsulin stratified by GCK and G6PC2, we noted divergent changes in these quantitative traits for GCK but parallel changes for G6PC2. We observed a similar pattern in METSIM.
  
  
  CONCLUSIONS
  Our data suggest that variation in GCK and G6PC2 have additive effects on both fasting glucose and insulin secretion.
authors.affiliation: Department of Preventive Medicine, Division of Biostatistics, Keck School of Medicine, University of Southern California, Los Angeles, California, USA.
authors.forename: Xia
authors.initials: X
authors.lastname: Li
authors.forename: Yu-Hsiang
authors.initials: YH
authors.lastname: Shu
authors.forename: Anny H
authors.initials: AH
authors.lastname: Xiang
authors.forename: Enrique
authors.initials: E
authors.lastname: Trigo
authors.forename: Johanna
authors.initials: J
authors.lastname: Kuusisto
authors.forename: Jaana
authors.initials: J
authors.lastname: Hartiala
authors.forename: Amy J
authors.initials: AJ
authors.lastname: Swift
authors.forename: Miwa
authors.initials: M
authors.lastname: Kawakubo
authors.forename: Heather M
authors.initials: HM
authors.lastname: Stringham
authors.forename: Lori L
authors.initials: LL
authors.lastname: Bonnycastle
authors.forename: Jean M
authors.initials: JM
authors.lastname: Lawrence
authors.forename: Markku
authors.initials: M
authors.lastname: Laakso
authors.forename: Hooman
authors.initials: H
authors.lastname: Allayee
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Buchanan
authors.forename: Richard M
authors.initials: RM
authors.lastname: Watanabe
mesh_terms: D000328:Adult; D000368:Aged; D001786:Blood Glucose / Q000378:metabolism*; D005215:Fasting; D005260:Female; D014644:Genetic Variation; D000081410:Germinal Center Kinases; D005952:Glucose-6-Phosphatase / Q000235:genetics*; D006801:Humans; D007328:Insulin / Q000097:blood / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000378:metabolism; D008297:Male; D017058:Mexican Americans / Q000235:genetics*; D008875:Middle Aged; D020641:Polymorphism, Single Nucleotide; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*
chemical_list: D001786:Blood Glucose; D000081410:Germinal Center Kinases; D007328:Insulin; D017346:Protein Serine-Threonine Kinases; D005952:Glucose-6-Phosphatase; C492194:G6PC2 protein, human