all subjects were consecutively recruited from the greater philadelphia area from 20062009 at the children 's hospital of philadelphia .
our study cohort consisted of 5,465 singleton children of european ancestry with recorded birth weight information .
all of these participants had their blood drawn in an 8-ml ethylenediamine tetraacetic acid blood collection tube and subsequently dna extracted for genotyping .
this study was approved by the institutional review board of the children 's hospital of philadelphia .
parental informed consent was given for each study participant for both the blood collection and subsequent genotyping .
we performed high - throughput genome - wide single nucleotide polymorphism ( snp ) genotyping using the illumina infinium ii humanhap550 or human 610 beadchip technology ( illumina , san diego , ca ) at the children 's hospital of philadelphia 's center for applied genomics , as described previously ( 23 ) .
the snps analyzed survived the filtering of the genome - wide dataset for snps with call rates < 95% , minor allele frequency < 1% , missing rate per person > 2% , and hardy - weinberg equilibrium p < 10 .
most loci described from gwa studies published to date have been found using either the affymetrix or illumina platform . in the event
a locus was reported using both the illumina and affymetrix arrays , we used the snps present on the illumina array . in the event of a signal
only being described on the affymetrix array , we either already had that snp on our illumina array or identified and used the best surrogate snp available based on the ceu hapmap ( supplementary table 1 , available in the online appendix at http://diabetes.diabetesjournals.org/cgi/content/full/db09-0506/dc1 ) .
we used two snps at the cdkal1 ( rs4712523 and rs7756992 ; r = 0.677 ) , hhex - ide ( rs1111875 and rs7923837 ; r = 0.698 ) , and pparg ( rs17793693 and rs6802898 ; r = 0.011 ) loci as the association with type 2 diabetes , taken from various gwa studies that reported various snps that were in imperfect linkage disequilibrium with each other .
in addition , rs4712523 is a proxy ( r = 1 ) for rs10946398 , which was previously associated with birth weight . from our database
, we eliminated outliers with birth weight < 1 or > 8 kg , i.e. , those individuals not within the credible range for birth weight at term , to avoid the potential consequences of error or mendelian causes of extreme birth weight .
each birth weight value was adjusted for each sex separately then expressed as a z score .
all statistical analyses were carried out using the software package plink v. 1.05 ( 24 ) .
ethnicity for our cohort was derived using the multidimensional scaling feature within plink . by treating birth weight as a quantitative trait ( treated as a z score after correcting for sex ) , association analysis for each snp
was carried out using linear regression analysis with the snp included as an independent variable ( coded as 0 , 1 , and 2 ) . with 5,465 subjects , the powers to detect 0.2 , 0.3 , 0.4 , 0.5 , 0.6 , 0.8 , and 1% variation at the p = 0.002 level ( i.e. , the corrected p value for the number of tests ) were 47.4 , 74.6 , 90.0 , 96.6 , 98.9 , 100 , and 100% , respectively .
all subjects were consecutively recruited from the greater philadelphia area from 20062009 at the children 's hospital of philadelphia .
our study cohort consisted of 5,465 singleton children of european ancestry with recorded birth weight information .
all of these participants had their blood drawn in an 8-ml ethylenediamine tetraacetic acid blood collection tube and subsequently dna extracted for genotyping .
this study was approved by the institutional review board of the children 's hospital of philadelphia .
parental informed consent was given for each study participant for both the blood collection and subsequent genotyping .
all subjects were consecutively recruited from the greater philadelphia area from 20062009 at the children 's hospital of philadelphia .
our study cohort consisted of 5,465 singleton children of european ancestry with recorded birth weight information .
all of these participants had their blood drawn in an 8-ml ethylenediamine tetraacetic acid blood collection tube and subsequently dna extracted for genotyping .
this study was approved by the institutional review board of the children 's hospital of philadelphia .
parental informed consent was given for each study participant for both the blood collection and subsequent genotyping .
we performed high - throughput genome - wide single nucleotide polymorphism ( snp ) genotyping using the illumina infinium ii humanhap550 or human 610 beadchip technology ( illumina , san diego , ca ) at the children 's hospital of philadelphia 's center for applied genomics , as described previously ( 23 ) .
the snps analyzed survived the filtering of the genome - wide dataset for snps with call rates < 95% , minor allele frequency < 1% , missing rate per person > 2% , and hardy - weinberg equilibrium p < 10 .
most loci described from gwa studies published to date have been found using either the affymetrix or illumina platform . in the event
a locus was reported using both the illumina and affymetrix arrays , we used the snps present on the illumina array . in the event of a signal
only being described on the affymetrix array , we either already had that snp on our illumina array or identified and used the best surrogate snp available based on the ceu hapmap ( supplementary table 1 , available in the online appendix at http://diabetes.diabetesjournals.org/cgi/content/full/db09-0506/dc1 ) .
we used two snps at the cdkal1 ( rs4712523 and rs7756992 ; r = 0.677 ) , hhex - ide ( rs1111875 and rs7923837 ; r = 0.698 ) , and pparg ( rs17793693 and rs6802898 ; r = 0.011 ) loci as the association with type 2 diabetes , taken from various gwa studies that reported various snps that were in imperfect linkage disequilibrium with each other .
in addition , rs4712523 is a proxy ( r = 1 ) for rs10946398 , which was previously associated with birth weight .
we performed high - throughput genome - wide single nucleotide polymorphism ( snp ) genotyping using the illumina infinium ii humanhap550 or human 610 beadchip technology ( illumina , san diego , ca ) at the children 's hospital of philadelphia 's center for applied genomics , as described previously ( 23 ) .
the snps analyzed survived the filtering of the genome - wide dataset for snps with call rates < 95% , minor allele frequency < 1% , missing rate per person > 2% , and hardy - weinberg equilibrium p < 10 .
most loci described from gwa studies published to date have been found using either the affymetrix or illumina platform . in the event
a locus was reported using both the illumina and affymetrix arrays , we used the snps present on the illumina array . in the event of a signal
only being described on the affymetrix array , we either already had that snp on our illumina array or identified and used the best surrogate snp available based on the ceu hapmap ( supplementary table 1 , available in the online appendix at http://diabetes.diabetesjournals.org/cgi/content/full/db09-0506/dc1 ) .
we used two snps at the cdkal1 ( rs4712523 and rs7756992 ; r = 0.677 ) , hhex - ide ( rs1111875 and rs7923837 ; r = 0.698 ) , and pparg ( rs17793693 and rs6802898 ; r = 0.011 ) loci as the association with type 2 diabetes , taken from various gwa studies that reported various snps that were in imperfect linkage disequilibrium with each other .
in addition , rs4712523 is a proxy ( r = 1 ) for rs10946398 , which was previously associated with birth weight .
from our database , we eliminated outliers with birth weight < 1 or > 8 kg , i.e. , those individuals not within the credible range for birth weight at term , to avoid the potential consequences of error or mendelian causes of extreme birth weight .
each birth weight value was adjusted for each sex separately then expressed as a z score .
from our database , we eliminated outliers with birth weight < 1 or > 8 kg , i.e. , those individuals not within the credible range for birth weight at term , to avoid the potential consequences of error or mendelian causes of extreme birth weight .
each birth weight value was adjusted for each sex separately then expressed as a z score .
all statistical analyses were carried out using the software package plink v. 1.05 ( 24 ) .
ethnicity for our cohort was derived using the multidimensional scaling feature within plink . by treating birth weight as a quantitative trait ( treated as a z score after correcting for sex ) , association analysis for each snp
was carried out using linear regression analysis with the snp included as an independent variable ( coded as 0 , 1 , and 2 ) . with 5,465 subjects , the powers to detect 0.2 , 0.3 , 0.4 , 0.5 , 0.6 , 0.8 , and 1% variation at the p = 0.002 level ( i.e. , the corrected p value for the number of tests ) were 47.4 , 74.6 , 90.0 , 96.6 , 98.9 , 100 , and 100% , respectively .
in our initial analysis , 12 snps corresponding to the 9 type 2 diabetes loci previously studied in the context of birth weight were investigated in our cohort , namely , tcf7l2 , hhex - ide , pparg , kcnj11 , slc30a8 , igf2bp2 , cdkal1 , cdkn2a/2b , and jazf1 ( 4,6 ) ( table 1 ) .
quantitative association results for previously studied type 2 diabetes risk alleles with birth weight in the european american cohort ( n = 5,465 ) , sorted by chromosomal location the direction of effect is shown for the minor allele in each case . *
major allele previously reported to be associated with type 2 diabetes ; * * p  0.002 .
 , regression coefficient for the test snp ; bp , base pair position ; maf , minor allele frequency ; n , number of subjects tested ; p , two - sided trend test p value ; r , value in linear regression ; t , test statistic . as a result ,
we observed strong association with rs7756992 ( p = 8 10 ) at the cdkal1 locus with low birth weight ; this snp yielded strongest association to type 2 diabetes in an icelandic gwa study carried out on the illumina humanhap500 platform ( 21 ) .
snps rs10946398 or rs7754840 at the same locus have been reported to be most strongly associated with type 2 diabetes from gwa studies on the affymetrix platform or the illumina humanhap300 beadchip ( 16,18,19 ) ; however , using a perfect surrogate , rs4712523 ( r = 1 ) , we only observed nominally significant association ( p = 0.01 ) .
it should be noted that rs10946398 and rs7756992 are far from being in perfect linkage disequilibrium ( r = 0.677 ) , thus the inclusion of both in this current study . unlike previous reports
, we did not observe association between rs1111875 at the hhex - ide locus and this trait ( 6 ) . in line with previous reports
, we also did not observe association between birth weight and tcf7l2 , pparg , kcnj11 , slc30a8 , igf2bp2 , cdkn2a/2b , or jazf1 ( 4,6,10 ) .
furthermore , we did not observe any significant association with risk alleles at other type 2 diabetes loci after correction for multiple testing for all 23 snps ( threshold p  0.002 ) ( supplementary table 2 ) .
we detected nominal association with rs1387153 ( p = 0.02 ) at the mtnr1b locus ; however , the corresponding type 2 diabetes risk allele was tracking with higher birth weight .
we also analyzed male and female subjects separately , but the effect of each locus on birth weight did not vary by sex ( supplementary tables 3 and 4 ) .
from this interim analysis of our ongoing gwa study of birth weight in a european american cohort , it is clear that the cdkal1 locus , which was uncovered in gwa analyses of type 2 diabetes , is strongly associated with birth weight in our study population .
this result clearly supports a previous report that came to a similar conclusion ( 6 ) .
however , the study by freathy et al . used a different snp , namely , rs10946398 , which was not present on our illumina beadchip ; we used a perfect surrogate , i.e. , rs4712523 ( r = 1 ) , that only yielded nominal significance ( p = 0.01 ) .
although they did not report for rs7756992 , we found that it gave us the strongest association ( p = 8 10 ) and was selected for this study because it yielded the strongest association to type 2 diabetes in an icelandic gwa study ( 21 ) .
secondly , we did not observe association between hhex - ide and birth weight , which is in contrast with what had been described previously ( 6 ) .
we acknowledge that our cohort is smaller than the original report ( 5,465 vs. 19,200 individuals ) ; indeed , this association was not observed ( p < 0.05 ) in the similarly sized 1958 birth cohort ( 6 ) .
the lack of available covariate data , such as gestational age , was also a limitation of this study .
therefore , it is possible that with a larger cohort with additional covariate data we may observe the association of this locus with birth weight ; however , it could also indicate that hhex - ide has a less pronounced impact on birth weight than cdkal1 .
consistent with the existing literature , we did not find any evidence of association between birth weight and tcf7l2 , pparg , kcnj11 , slc30a8 , igf2bp2 , cdkn2a/2b , or jazf1 ( 4,6,10 ) . given the monogenic precedent for opposing effects of maternal and fetal genotype ( 25 ) , it is possible that effects of common type 2 diabetes alleles could be masked by this phenomenon .
it has been shown that cdkal1 is expressed in the rat pancreatic -cell line ins-1 ( 21 ) .
homozygous carriers of the risk allele have been shown to have a 22% lower corrected insulin response than individuals who are wild - type carriers .
it has been suggested that cdkal1 might influence the secretion of insulin by interacting with cdk5 ( 21 ) .
our data contributes another piece of evidence supporting the hypothesis , namely , that the same genotype conferring lower birth weight can also confer higher type 2 diabetes risk later in life .
cdkal1 was first described in the context of type 2 diabetes in both european caucasians and in han chinese ( 21 ) ; as such , it would be interesting to examine whether the association of cdkal1 with lower birth weight also stands in this and other ethnicities , such as african americans and hispanics . in conclusion
, we strongly confirm that the established type 2 diabetes locus cdkal1 also influences birth weight .
however , we do not observe such association with tcf7l2 , hhex - ide , cdkn2a/2b , or jazf1 .
in addition , of all the other established type 2 diabetes loci to date , we do not observe a convincing role for them in the determination of birth weight .
 objectivea number of studies have found that reduced birth weight is associated with type 2 diabetes later in life ; however , the underlying mechanism for this correlation remains unresolved . 
 recently , association has been demonstrated between low birth weight and single nucleotide polymorphisms ( snps ) at the cdkal1 and hhex - ide loci , regions that were previously implicated in the pathogenesis of type 2 diabetes . in order to investigate whether type 2 diabetes risk  conferring alleles associate with low birth weight in our caucasian childhood cohort , we examined the effects of 20 such loci on this trait.research design and methodsusing data from an ongoing genome - wide association study in our cohort of 5,465 caucasian children with recorded birth weights , we investigated the association of the previously reported type 2 diabetes  associated variation at 20 loci including tcf7l2 , hhex - ide , pparg , kcnj11 , slc30a8 , igf2bp2 , cdkal1 , cdkn2a/2b , and jazf1 with birth weight.resultsour 
 data show that the minor allele of rs7756992 ( p = 8  105 ) at the cdkal1 locus is strongly associated with lower birth weight , whereas a perfect surrogate for variation previously implicated for the trait at the same locus only yielded nominally significant association ( p = 0.01 ; r2 rs7756992 = 0.677 ) . 
 however , association was not detected with any of the other type 2 diabetes loci studied.conclusionswe observe association between lower birth weight and type 2 diabetes risk  conferring alleles at the cdkal1 locus . 
 our data show that the same genetic locus that has been identified as a marker for type 2 diabetes in previous studies also influences birth weight . 
RESEARCH DESIGN AND METHODS
Research subjects
European American Pediatric cohort from Philadelphia.
Genotyping
Illumina Infinium assay.
Analysis
Normalization of birth weight data.
Association.
RESULTS
DISCUSSION