diabetes decreases the overall life expectancy and cause a heavy burden on public health ( 1 ) .
moreover , the asia - pacific region is considered to be on the verge of an emerging diabetes epidemic ( 2 ) .
the development of type 2 diabetes is affected by genetic and environmental determinants ( 3 ) .
recently , one study investigated whether common variants of functional and positional candidate genes , including adrb3 , pparg , enpp1 and capn10 , were determinants of type 2 diabetes ( 4 ) .
enpp1 , also called k121q , has a glutamine substitution for lysine at codon 121 ( 5 ) .
type 2 diabetes is characterized by insulin resistance ( 6 ) , and enpp1 plays an important role in insulin resistance ( 7 , 8) .
enpp1 interacts with -subunit of the insulin receptor to interrupt signaling ( 9 ) . in previous studies , the k121q polymorphism of the human pc-1 gene was strongly associated with insulin resistance ( 1 , 3 , 7 , 10 - 12 ) . however , there was no association between insulin resistance and the k121q variant ( 13 , 14 ) .
in addition , there were discrepancies for the impact of enpp1 polymorphism on obesity between ethnic groups ( 5 , 10 , 13 , 15 - 19 ) .
obesity increases the concentration of insulin in plasma and is the major contributor of insulin resistance ( 20 ) .
obesity appears to be an effect modifier of type 2 diabetes in d1057 carriers ( 21 ) .
the association of obesity with the genetic variant of the insulin receptor substrate was identified in other studies ( 21 , 22 ) . in the chinese han population ,
the pc-1 q121 allele was associated with insulin resistance . in women , carriers of the q allele
had an increased risk for obesity development ( 3 ) . in caucasians and african - americans , 121q carriers had an association with increased body mass index ( bmi ) ( 23 ) , and the three - allele risk type haploid qdeltg with the q allele increased the risk for obesity ( 24 )
however , in the danish population , there were no differences in the distribution of frequencies of dominant types ( kk wild type and kq / qq variant type ) and alleles ( 19 ) .
the complexity of type 2 diabetes is related to factors such as genetic heterogeneity , interactions between genes , and the modulating role played by the environment ( 4 ) . in spite of these limitations , studies of type 2 diabetes and genetic factors of obesity
can predict the risks for development of both type 2 diabetes and obesity in order to assist primary prevention , and korea is an appropriate country for such studies because of the homogeneity of racial composition and lifestyle ( 25 ) .
therefore , the aim of this study was to analyze the presence of the enpp1 polymorphism , not studied yet in korean population , to identify the association between genotypes and allele with type 2 diabetes and obesity .
this company is an electric power company located at kori , yonggwang , ulchin , wolsung , and seoul in korea .
there were 195 male workers ( age 48.26.7 yr , bmi 24.672.64 kg / m ) who were diagnosed as diabetics during medical examinations conducted from march 2004 to october .
the 1,750 male workers ( age 45.27.7 yr , bmi 24.772.64 kg / m ) in the control group were selected randomly .
subjects were included if they met one of the criteria below and their onset age was older than 20 yr old to exclude type 1 diabetes : 1 ) blood - sugar level before a meal exceeded 126 mg / dl twice or more ; 2 ) blood - sugar level before a meal exceeded 126 mg / dl once or more and blood - sugar level two hours after a meal exceeded 200 mg / dl ; 3 ) those who reported that he had a history of diabetes in the questionnaire and being taken oral hypoglycemic agents .
the workers included in the obesity group were those whose bmi was 25 kg / m or more . after collecting a blood sample from vein in fasting ( 8 hr ) status , we measured the blood - sugar level , insulin , and lipid profile
. we also measured height and weight to calculate bmi . if fasting glucose levels were greater than 126 mg / dl
, we checked the 2 hr post - prandial plasma glucose level at each site within 1 month .
height and weight were measured by autoanalyzer ( health guard , fanics , seoul , korea ) .
the fasting blood level was analyzed by glucose - oxidase assay using an autochemistry analyzer . to determine the lipid profile ,
total cholesterol was analyzed by enzyme assay using cholesterol oxidase ( cod ) , high density lipoprotein ( hdl ) cholesterol by glycerol phosphate oxidase assay , low density lipoprotein ( ldl ) cholesterol by direct surfactant assay .
we carried out this study under the approval by the ethnics committee of the asan medical center , and obtained written consent from all subjects , providing subjects with sufficient explanation to obtain informed consent .
we extracted genomic dna from buffy coats using the generall blood sv kit ( general biosystem , seoul , korea ) and following the instructions suggested by the manufacturer .
the method of genotyping used to identify the k121q polymorphism in enpp1 exon 4 was polymerase chain reaction - restriction fragment length polymorphism ( pcr - rflp ) , using dna treated with a restriction enzyme after pcr , based on the paper reported by abate et al .
we carried out student 's t - test to analyze the effects of genotypes on biochemical parameters using genotypes as factors .
the hardy - weinberg equilibrium was computed based on the  goodness - of - fit test .
we also investigated the differences in frequencies of genotypes between type 2 diabetic and normal groups , and between obesity and normal groups by fisher 's exact test .
the spss 12.0 ( for window ) statistical software package was used for statistical analysis .
this company is an electric power company located at kori , yonggwang , ulchin , wolsung , and seoul in korea .
there were 195 male workers ( age 48.26.7 yr , bmi 24.672.64 kg / m ) who were diagnosed as diabetics during medical examinations conducted from march 2004 to october .
the 1,750 male workers ( age 45.27.7 yr , bmi 24.772.64 kg / m ) in the control group were selected randomly .
subjects were included if they met one of the criteria below and their onset age was older than 20 yr old to exclude type 1 diabetes : 1 ) blood - sugar level before a meal exceeded 126 mg / dl twice or more ; 2 ) blood - sugar level before a meal exceeded 126 mg / dl once or more and blood - sugar level two hours after a meal exceeded 200 mg / dl ; 3 ) those who reported that he had a history of diabetes in the questionnaire and being taken oral hypoglycemic agents .
the workers included in the obesity group were those whose bmi was 25 kg / m or more . after collecting a blood sample from vein in fasting ( 8 hr ) status , we measured the blood - sugar level , insulin , and lipid profile
. we also measured height and weight to calculate bmi . if fasting glucose levels were greater than 126 mg / dl
, we checked the 2 hr post - prandial plasma glucose level at each site within 1 month .
height and weight were measured by autoanalyzer ( health guard , fanics , seoul , korea ) .
the fasting blood level was analyzed by glucose - oxidase assay using an autochemistry analyzer . to determine the lipid profile ,
total cholesterol was analyzed by enzyme assay using cholesterol oxidase ( cod ) , high density lipoprotein ( hdl ) cholesterol by glycerol phosphate oxidase assay , low density lipoprotein ( ldl ) cholesterol by direct surfactant assay .
we carried out this study under the approval by the ethnics committee of the asan medical center , and obtained written consent from all subjects , providing subjects with sufficient explanation to obtain informed consent .
we extracted genomic dna from buffy coats using the generall blood sv kit ( general biosystem , seoul , korea ) and following the instructions suggested by the manufacturer .
the method of genotyping used to identify the k121q polymorphism in enpp1 exon 4 was polymerase chain reaction - restriction fragment length polymorphism ( pcr - rflp ) , using dna treated with a restriction enzyme after pcr , based on the paper reported by abate et al .
we carried out student 's t - test to analyze the effects of genotypes on biochemical parameters using genotypes as factors .
the hardy - weinberg equilibrium was computed based on the  goodness - of - fit test .
we also investigated the differences in frequencies of genotypes between type 2 diabetic and normal groups , and between obesity and normal groups by fisher 's exact test .
the spss 12.0 ( for window ) statistical software package was used for statistical analysis .
the frequencies of the kk type , kq type , and qq type in enpp1 k121q were 82.1% , 17% and 0.9% , respectively .
the homozygous type of q carrier ( qq type ) was added to the heterozygous type ( kq type ) because the frequency of qq type was very low ( 0.9% ) .
we investigated the differences in age , blood pressure , bmi , and results of clinical examinations according to genotypes of enpp1 k121q between the type 2 diabetic and non - diabetic groups ( table 1 ) . when type 2 diabetics and non - diabetics were pooled ( n=1,945 ) , there were no significant differences in bmi , systolic pressure , diastolic pressure , glucose value in fasting status , total cholesterol , ldl cholesterol , hdl cholesterol , triglyceride , c - reactive protein , and homa - ir between the kk type and kq+qq type .
in addition , there were no significant differences in the same characteristics above between type 2 diabetic group and non - diabetic groups ( table1 ) , and between the obese group and non - obese groups ( table2 ) .
the frequencies of genotypes were in accordance with the hardy - weinberg equilibrium ( p=0.85 ) .
the odds ratio of having a kq+qq genotype was 0.85 for diabetics versus non - diabetics .
the odds ratio of having a q allele was 0.91 for diabetics versus non - diabetics .
however , there was no significant difference in the genotypic and allelic distribution between type 2 diabetics and non - diabetics ( table3 ) .
the odds of a kq+qq genotype were 0.93 for obese versus non - obese subjects . furthermore , the odds of having a q allele were 0.96 for obese versus non - obese subjects
. however , there was no significant difference in the genotypic and allelic distribution between obese and non - obese ( table4 ) .
the frequency of the kk type in enpp1 k121q genotypes was 82.1% , that of kq+qq type was 17.9% and that of q allele was 9.4% .
there was no statistically significant difference in the distribution among these genotypes and alleles ( p=0.81 , p=0.89 , respectively ) , although the 121q carrier and q allele in obese and/or diabetics seemed to differ slightly from those in the non - obese non - diabetics ( reference group ) . in determining the prevalence of the q allele carriers ( kq and qq subjects ) and q allele
, there were no significant differences in the genotypic and allelic distribution with the respect to any phenotypes ( data not shown ) .
after adjusting for the effects of obesity , the probability of type 2 diabetes in kq+qq type was 0.858 ( data not shown ) and that in q allele was 1.095 , showing no significant difference ( table 5 ) .
moreover , after adjusting for the effects of type 2 diabetes , the probability of developing obesity in the kq+qq type was 0.936 ( data not shown ) and that in the q allele was 1.038 , showing no significant difference ( table 6 ) .
the results of studies of the association between enpp1 k121q variants and both type 2 diabetes and obesity in several races are disparate .
we carried out this study to investigate the association of k121q variants with type 2 diabetes and obesity in korean male workers .
insulin resistance is a major component of the pathogenesis of type 2 diabetes ( 27 ) , and insulin receptor kinase activity is impaired in muscle and other insulin - sensitive tissue of many type 2 diabetic patients ( 28 ) , and then a potential inhibitor of the insulin receptor tyrosine kinase is identified as the plasma - cell membrane differentiation antigen-1 ( pc-1 ) ( 29 ) .
therefore , it is significant to analyze enpp1 ( pc-1 ) polymorphism . in the previous studies of the association between type 2 diabetes and polymorphism in enpp1 , the k121q missense mutation increased the odds ratio ( or ) for type 2 diabetes in dominican ( 10 ) , south asian , caucasian ( 16 ) , finnish ( 18 ) , and french populations ( 24 ) .
moreover , according to a meta - analysis of the association between enpp1 k121q variant and type 2 diabetes , the odds ratios were 1.30 ( 95% confidence interval [ ci ] , 1.13 - 1.50 ) ( 16 ) and 1.17 ( 95% ci , 1.10 - 1.25 ) ( 19 ) , showing significant association . in this study , 121q was not associated with type 2 diabetes , showing consistent results with those in the japanese population ( 5 ) , danish caucasians ( 13 ) , oji - cree population ( 17 ) , finnish population ( 18 ) , and danish white subjects ( 19 ) .
most type 2 diabetes in koreans is characterized by non - obesity , thus the enpp1 k121q mutant relevant to insulin resistance possibly could be a candidate gene that is not appropriate to explain susceptibility to type 2 diabetes .
this can be a possible explanation for the lack of association between enpp1 121q carrier and type 2 diabetes in this study .
obesity is a main risk factor for the development of type 2 diabetes ( 20 ) and there is linear association between obesity and type 2 diabetes ( 3 ) . in previous studies of the association between obesity and polymorphism in enpp1 ,
121q carriers and/or q allele were associated with obesity in the chinese han population ( bmi of obesity group 27 kg / m ) ( 3 ) , caucasians ( bmi of obesity group > 90th percentile ) , african - american adults ( bmi of obesity group > 80th percentile ) ( 23 ) , french population ( bmi of obesity group 95th percentile ) ( 24 ) , and dominican population ( bmi of obesity group 30 kg / m ) ( 10 ) . however , in this study ( bmi of obesity group 25 kg / m ) , there was no difference in distribution between obesity and 121q carriers and presence of the q allele .
this result was consistent with those from a study of 7,333 danes ( 19 ) and a spanish population ( 14 ) in which the bmi of the obesity group was 25 kg / m or higher . on the other hand , in matsuoka 's study ,
the percentage of subjects whose bmi was 30 kg / m or higher was too low ( 2.5% ) to investigate the effect of k121q genotype on obesity .
the results of the present study showed that the frequencies of the q allele was 8.7% in the type 2 diabetic group and 9.2% in the obesity group , which was lower than those in finnish and swedish populations ( 12.9 - 15.1% ) ( 11 ) , danish caucasians ( 14 - 16% ) ( 13 ) , south asians in chennai ( 14% ) , caucasians in dallas ( 16% ) , south asians in dallas ( 19% ) ( 16 ) , the dominican population ( 54.2% ) ( 10 ) and , black children ( 77% ) ( 30 ) .
the frequencies of the q allele investigated in this study might have a smaller statistical power to explain any association with either type 2 diabetes or obesity with 121q carriers ( kq+qq ) and/or the q allele . in conclusion
, the present study suggests that the enpp1 k121q polymorphism was not associated with type 2 diabetes and obesity .
the results of negative associations in this study might be attributable to the low prevalence of obesity , relatively younger age , and low frequencies of the 121q carriers .
large and prospective studies are needed to confirm this preliminary observation in the korean population .
 type 2 diabetes is characterized by insulin resistance , and enpp1 plays an important role in insulin resistance . 
 we investigated the association of the enpp1 k121q polymorphism with both diabetes and obesity ( body mass index [ bmi ] ) in korean male workers . 
 the study design was case - control . 
 subjects were 1,945 male workers ( type 2 diabetes , 195 ; non - diabetes , 1,750 ) of nuclear power plants who received examinations from march to october in 2004 . 
 we collected venous blood samples under fasting ( 8 hr ) conditions , calculated bmi by height and weight , and assessed relevant biochemical factors . 
 the results of this study demonstrated that the enpp1 121q genotype ( kq+qq types ) was not associated with type 2 diabetes ( odds ratios [ or ] , 0.854 ; 95% confidence interval [ ci ] , 0.571 - 1.278 ) or obesity ( or , 0.933 ; 95% ci , 0.731 - 1.190 ) . 
 in addition , the frequency of the q allele was not related to type 2 diabetes ( or , 0.911 ; 95% ci , 0.630 - 1.319 ) or obesity ( or , 0.962 ; 95% ci , 0.767 - 1.205 ) . 
 we concluded that the enpp1 121q allele is not a critical determinant for either diabetes or obesity in korean males . 
 the discordance between the results of this study and those derived from studies of dominican , south asian , caucasian , finnish , and french populations might be due to differences in genetic backgrounds between these populations . 
INTRODUCTION
MATERIALS AND METHODS
Subjects
DNA extraction and PCR
Statistical analysis
RESULTS
DISCUSSION