Studies of relationships between variation of the human G protein-coupled receptor 40 Gene and Type 2 diabetes and insulin release.
OBJECTIVE
Recently, a novel human G protein-coupled receptor 40 (GPR40), which is predominantly expressed in pancreatic islets, was shown to mediate an amplifying effect of long-chain fatty acids on glucose-induced insulin secretion. The present aim was to examine the coding region of GPR40 for variation and to assess whether identified variants confer an increased risk of Type 2 diabetes or altered insulin release.


METHODS
Mutation analysis was performed in 43 patients with Type 2 diabetes, 18 normal glucose-tolerant subjects, and 3 maturity-onset of diabetes in the young (MODY) X patients using direct sequencing. Genotyping was performed using polymerase chain reaction (PCR)-generated primer extension products analysis by high throughput chip-based mass spectrometry (MALDI-TOF). The potential impact of GPR40 mutations on [(3)H]-myo-inositol turnover was estimated in COS-7 cells after stimulation with various concentrations of 5,8,11-eicosatriynoic acid.


RESULTS
Two nucleotide substitutions, an Arg211His polymorphism and a rare Asp175Asn mutation, were identified. Both variants showed EC(50) values similar to the wild type. However, the maximal efficacy of the rare Asp175Asn was 39% lower compared with the wild type (P = 0.01). The Arg211His polymorphism had a similar allele frequency among 1384 Type 2 diabetic patients [MAF%; 23.4 (95% CI: 21.8-25.0)] and 4424 middle-aged glucose-tolerant subjects [24.1% (23.2-25.0)]. A genotype-quantitative trait study of 5597 non-diabetic, middle-aged subjects from the Inter99 cohort showed no significant differences in oral glucose tolerance test (OGTT)-derived estimates of insulin release between carriers of various GPR40 genotypes.


CONCLUSIONS
Variations in the coding region of GPR40 do not appear to be associated with Type 2 diabetes or insulin release alterations.
Hamid
Y H
YH
Steno Diabetes Center, DK-2820 Gentofte, Denmark. yah@steno.dk
Vissing
H
H
Holst
B
B
Urhammer
S A
SA
Pyke
C
C
Hansen
S K
SK
Glümer
C
C
Borch-Johnsen
K
K
Jørgensen
T
T
Schwartz
T W
TW
Pedersen
O
O
Hansen
T
T
D016022:Case-Control Studies; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D008875:Middle Aged; D009154:Mutation / Q000235:genetics*; D010375:Pedigree; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D043562:Receptors, G-Protein-Coupled / Q000235:genetics*
C473034:FFAR1 protein, human; D007328:Insulin; D043562:Receptors, G-Protein-Coupled