the study used data from the cross - sectional population - based 1998 singapore national health survey ( nhs98 ; n = 4,723 ) .
genotype data were available for 3,734 subjects comprising 2,520 chinese , 693 malay , and 521 asian indians .
a total of 1,881 chinese subjects with normal glucose tolerance ( ngt ) had previously served as the control subjects for the singapore replication arm in our original report ( 6 ) , whereas type 2 diabetes case subjects were from a separate study ( the singapore diabetes cohort study ) . in this present study ,
all subjects ( including subjects with ngt , impaired fasting glucose , impaired glucose tolerance [ igt ] , and type 2 diabetes ) were derived from the nhs98 study .
details of the nhs98 survey have been previously described in greater detail ( 9 ) .
briefly , this was a population - based , cross - sectional survey conducted between september and november in 1998 .
the reference population was 2.16 million chinese , malay , and asian indian singapore residents aged between 18 and 69 years .
the survey was based on the world health organization ( who)-recommended model for field surveys of diabetes and other noncommunicable diseases and the who monica protocol for population surveys .
the research protocol for nhs98 was approved by the singapore general hospital institutional review board ( # 54/2001 ) .
fasting blood samples were collected for glucose and insulin after an overnight fast of 10 h. all subjects underwent a 75-g oral glucose tolerance test except those taking oral hypoglycemic agents or insulin .
subjects were classified as having diabetes if they gave a history of diabetes or if their fasting glucose was > 7 mmol / l or 2-h post - challenge glucose > 11.1 mmol / l .
mmol / l and impaired glucose tolerance as 2-h post - challenge glucose of 7.811.1 mmol / l .
insulin resistance was estimated using the homeostasis model assessment method ( homa - ir ) ( 10 ) .
-cell function was assessed using the corrected insulin response at 120 min ( cir120 ) ( 11 ) .
genotyping of four snps in intron 15 of kcnq1 rs2237897 ( c > t ) , rs2237895 ( a > c ) , rs2237892 ( c > t ) , and rs2283228 ( a > c ) was performed using the taqman snp genotyping assay ( applied biosystems , foster city , ca ) . genotyping
success rate for rs2237897 , rs2237895 , rs2237892 , and rs2283228 was 92 , 99 , 92 , and 87% , respectively .
to assess reproducibility , 1% of samples were analyzed in duplicate ; genotyping was 100% concordant for these samples .
minor allele frequency , hardy - weinberg equilibrium , and linkage disequilibrium ( ld ; reported using r ) were estimated using haploview ( 12 ) .
the distribution of glucose and insulin measures were skewed and therefore normalized by natural logarithmic transformation .
linear regression analyses were performed to study the associations between diabetes - related traits with genotypic groups .
individuals were as assigned as 0/1/2 according to their number of minor alleles under an additive model of inheritance .
there was no significant heterogeneity between the sexes ( p > 0.05 ) , and subsequent analyses were performed with the sexes combined and adjusted for sex .
linear regression with adjustment for ethnicity was used to estimate the summary effect size of the snps in the combined sample from the three ethnic groups .
logistic regression was used to estimate the association between kcnq1 snps and type 2 diabetes .
all analyses were stratified by ethnic group and adjusted for age , sex , and bmi ( where appropriate ) .
analysis of association with -cell function was further adjusted for insulin resistance ( 13 ) .
fasting blood samples were collected for glucose and insulin after an overnight fast of 10 h. all subjects underwent a 75-g oral glucose tolerance test except those taking oral hypoglycemic agents or insulin .
subjects were classified as having diabetes if they gave a history of diabetes or if their fasting glucose was > 7
mmol / l and impaired glucose tolerance as 2-h post - challenge glucose of 7.811.1 mmol / l .
insulin resistance was estimated using the homeostasis model assessment method ( homa - ir ) ( 10 ) .
-cell function was assessed using the corrected insulin response at 120 min ( cir120 ) ( 11 ) .
genotyping of four snps in intron 15 of kcnq1 rs2237897 ( c > t ) , rs2237895 ( a > c ) , rs2237892 ( c > t ) , and rs2283228 ( a > c ) was performed using the taqman snp genotyping assay ( applied biosystems , foster city , ca ) . genotyping
success rate for rs2237897 , rs2237895 , rs2237892 , and rs2283228 was 92 , 99 , 92 , and 87% , respectively .
to assess reproducibility , 1% of samples were analyzed in duplicate ; genotyping was 100% concordant for these samples .
minor allele frequency , hardy - weinberg equilibrium , and linkage disequilibrium ( ld ; reported using r ) were estimated using haploview ( 12 ) . the distribution of glucose and insulin measures were skewed and therefore normalized by natural logarithmic transformation .
linear regression analyses were performed to study the associations between diabetes - related traits with genotypic groups .
individuals were as assigned as 0/1/2 according to their number of minor alleles under an additive model of inheritance .
there was no significant heterogeneity between the sexes ( p > 0.05 ) , and subsequent analyses were performed with the sexes combined and adjusted for sex .
linear regression with adjustment for ethnicity was used to estimate the summary effect size of the snps in the combined sample from the three ethnic groups .
logistic regression was used to estimate the association between kcnq1 snps and type 2 diabetes .
all analyses were stratified by ethnic group and adjusted for age , sex , and bmi ( where appropriate ) .
analysis of association with -cell function was further adjusted for insulin resistance ( 13 ) .
the anthropometric and biochemical characteristics of the participants are detailed in table 1 . among these individuals
, there was a higher prevalence of type 2 diabetes among the malay and asian indian populations and a lower mean bmi and fasting glucose level among the chinese population .
clinical characteristics of the nhs98 study population by ethnicity data are means  sd unless otherwise stated .
units for insulin120(i ) are given in mmol / l and for glucose120(g120 ) in mg / dl .
subjects taking diabetes medication were excluded ( 59 chinese , 35 malays , and 44 asian indians ) .
allele frequency for rs2237897 , rs2237895 , rs2237892 , and rs2283228 were similar between the chinese and malays but different in asian indians ( table 2 ) .
rs2237895 was in weak ld with rs2237897 , rs2237892 , and rs2283228 ( r < 0.25 ) , whereas moderate ld was observed between rs2237897 , rs2237892 , and rs2283228 ( chinese : r = 0.560.79 malay : r = 0.740.86 , asian indian : r = 0.390.62 ) ( supplemental fig .
all snps in the chinese and malays were in hardy - weinberg equilibrium ( p > 0.05 ) . in the asian indians , three of the snps that had low minor allele frequency ( rs2237897 , rs2237892 , and rs2283228 ) were not in the hardy - weinberg equilibrium .
association of kcnq1 genetic variants with type 2 diabetes in the chinese , malay , and asian indian population in singapore risk allele denoted in bold .
* p values adjusted for age , sex , bmi , and ethnicity ( for combined analysis ) . table 2 shows the association between kcnq1 snps with type 2 diabetes in the chinese , malay , and asian indian population in singapore .
significant associations were observed in the chinese , with rs2237897 showing the strongest effect : odds ratio ( or ) 1.50 ( 1.151.96 ) , p = 0.003 . in the combined sample of the three ethnic groups , the risk alleles of rs2237897 ( c ) , rs2237892 ( c ) , and rs2283228 ( a )
were also associated with type 2 diabetes in our study , consistent with previous reports ( 6,7 ) . of these , rs2237897 showed the strongest association ( or 1.48 [ 1.201.83 ] , p = 0.0003 ) . in the combined sample of only chinese and malays subjects ,
the association with rs2237897 remained significant ( or 1.45 [ 1.161.81 ] , p = 0.001 ) .
the risk alleles for rs2237897 , rs2237892 , and rs2283228 showed statistically significant association with higher fasting glucose levels ( p = 0.014 , 0.011 , and 0.034 , respectively ) and reduced cir120(p = 0.007 , 0.013 , and 0.014 , respectively ) in the chinese population . after restricting to subjects without diabetes , the association remained significant with cir120(p = 0.011 , 0.020 , and 0.015 , respectively ; online appendix table 1 ) .
a similar trend was observed among the malays and asian indians , although the associations did not reach statistical significance , possibly because of the limited sample sizes for these minority ethnic groups . in the combined analysis , rs2237897 and rs2237892
were significantly associated with fasting glucose levels ( p = 0.029 and p = 0.021 , respectively ) , whereas rs2237897 , rs2237892 , and rs2283228 were significantly associated with lower -cell function ( cir120 ) ( p = 0.013 , 0.021 , and 0.020 , respectively ) .
these snps also showed associations with bmi in the malay population and waist - to - hip ratio in asian indians .
however , these associations were no longer statistically significant in the combined analysis . based on a risk allele frequency of between 0.3 and 0.6
, power calculations estimate that the combined sample provided 90% power to detect a 10% change in the examined traits .
combined estimates were obtained using linear regression with adjustment for ethnicity . * additionally adjusted for bmi and excluding subjects taking diabetic medication ( 59 chinese , 35 malays , and 44 asian indians ) .
values were log - transformed to improve normality in regression analysis , and adjusted means were subsequently back - transformed .
polymorphisms within kcnq1 have recently been shown to be strongly associated with an increased risk of type 2 diabetes in the east asian and european populations ( 6,7 ) .
of the three polymorphisms within kcnq1 previously described , rs2237897 appeared to have the strongest association with type 2 diabetes ( 6 ) , whereas another study reported the strongest association with rs2237892 ( 7 ) .
consistent with these findings , we found that both these snps were significantly associated with type 2 diabetes in the combined analysis of three ethnic groups .
in addition , the presence of the risk allele for kcnq1 variants rs2237897 , rs2237892 , and rs2283228 were associated with increased fasting glucose level and decreased -cell function in the chinese population and combined sample .
( 7 ) , which reported an association of these kcnq1 variants with -cell function . together , these findings corroborate the hypothesis that the role of this protein in the pathogenesis of type 2 diabetes is likely mediated through its effects on the pancreatic -cell , although there is still a possibility that these polymorphisms may increase the risk of type 2 diabetes through regulation of nearby genes .
in contrast , there was no association between rs2237895 with any diabetes - related traits , specifically highlighting the importance of the polymorphisms rs2237897 , rs2237892 , and rs2283228 ( which are in moderate ld ) in increasing the risk of developing type 2 diabetes .
further fine mapping of snps in kcnq1 , especially within the ld block containing rs2237897 and rs2237892 , may allow the identification of the causal variant .
kcnq1 is located on 11p15.5 , which encodes the pore - forming -subunit of the iks kchannel , which is expressed mainly in the heart and , to a lesser extent , the inner ear , stomach , small and large intestine , liver , and kidney .
kcnq1 is also expressed in the pancreas , where it is coexpressed with products of other regulators such as kcne1 , which may alter its biophysical characteristics and role ( 15 ) .
as such , it is plausible that polymorphisms within the kcnq1 gene alter the properties and role of the iks kchannel , causing decreased pancreatic -cellfunction and insulin production , leading eventually to hyperglycemia . whereas we do appreciate that the associations observed in the chinese do not represent an independent replication , since the controls used are largely the same as those in the study by unoki et al .
( 6 ) , we have provided data on malays and indians and , in our opinion , it was reassuring that similar trends for an effect of these three polymorphisms on association with type 2 diabetes , fasting glucose , and -cell function were also observed in the malay and asian indian subjects , even though their limited numbers certainly resulted in a reduction of study power .
although associations with bmi in malays and waist - to - hip ratio in asian indians were found , the smaller sample sizes for these ethnic groups , together with the fact that these observations were not found in other ethnic groups , inevitably led us to be cautious in interpreting these findings . one caveat of this study is that we only examined the snps , which showed the strongest association , identified by unoki et al .
although the chinese show strong and consistent associations with these snps , the association among malays and asian indians is less clear .
further fine mapping of the kcnq1 locus , for instance , through deep dna resequencing may allow the identification of population - specific causative variants .
the use of cir120represented a limitation of our study , since it only served as an approximate measure of -cell function , which may be better assessed using the cir30 .
thus , if cir30measurements were available , the positive associations that had been observed in our study may be further strengthened .
it has also been suggested that cir120could inadvertently capture information on additional aspects of glucose intolerance instead of insulin secretion alone .
the previous finding of the association between cir30with kcnq1 snps , in nondiabetic european subjects of the botnia prospective study during their follow - up visit ( p = 0.024 ) ( 7 ) , however , appeared to corroborate our hypothesis that these snps may exert their effect on type 2 diabetes through an effect on insulin secretion . in conclusion ,
the risk alleles of rs2237897 , rs2237892 , and rs2283228 within the kcnq1 gene are associated with decreased pancreatic -cell function and fasting glucose levels , suggesting that the impact of these polymorphisms on the risk of type 2 diabetes may be mediated through an impact on -cell function rather than insulin resistance .
further studies will be useful to replicate these promising findings and to fully delineate the role of kcnq1 and its related pathways in the pathogenesis of type 2 diabetes .
 objectivethe potassium voltage - gated channel , kqt - like subfamily , member 1 ( kcnq1 ) has been found through a genome - wide association study to be a strong candidate for conferring susceptibility to type 2 diabetes in east asian and european populations . 
 our objective was to describe the association between polymorphisms at the kcnq1 locus with insulin resistance , -cell function , and other type 2 diabetes  related traits in a sample of chinese , malays , and asian indians living in singapore.research design and methodswe examined the associations between four previously reported kcnq1 single - nucleotide polymorphisms ( snps ) with type 2 diabetes  related traits in 3,734 participants from the population - based 1998 singapore national health survey cohort ( 2,520 chinese , 693 malay , and 521 asian indians ) . 
 insulin resistance was calculated from fasting insulin and glucose using the homeostasis model assessment method , whereas pancreatic -cell function was assessed using the corrected insulin response at 120 min ( cir120).resultssnps rs2237897 , rs2237892 , and rs2283228 were significantly associated with type 2 diabetes ( odds ratio [ or ] 1.48 , p = 3  104 ; or 1.38 , p = 0.002 ; or 1.31 , p = 0.012 , respectively ) . within the chinese population , 
 the risk alleles for rs2237897 , rs2237892 , and rs2283228 were significantly associated with higher fasting glucose levels ( p = 0.014 , 0.011 , and 0.034 , respectively ) and reduced cir120(p = 0.007 , 0.013 , and 0.014 , respectively ) . 
 a similar trend was observed among the malay and asian indian minority groups , although this did not reach statistical significance because of limited sample sizes.conclusionsthe increased risk for type 2 diabetes associated with kcnq1 is likely to be caused by a reduction in insulin secretion . 
 further studies will be useful to replicate these findings and to fully delineate the role of kcnq1 and its related pathways in disease pathogenesis . 
RESEARCH DESIGN AND METHODS
Biological measures.
SNP genotyping.
Statistical analysis.
RESULTS
DISCUSSION
Supplementary Material