The Relationship between Native American Ancestry, Body Mass Index and Diabetes Risk among

13 Pages·2015·0.45 MB·English

RESEARCHARTICLE
The Relationship between Native American
Ancestry, Body Mass Index and Diabetes Risk
among Mexican-Americans
HaoHu,ChadD.Huff,YukoYamamura,XifengWu,SaraS.Strom*
DepartmentofEpidemiology,UniversityofTexasMDAndersonCancerCenter,Houston,Texas,United
StatesofAmerica
*[email protected]
Abstract
Higherbodymassindex(BMI)isawell-establishedriskfactorfortype2diabetes,andrates
ofobesityandtype2diabetesaresubstantiallyhigheramongMexican-Americansrelative
tonon-HispanicEuropeanAmericans.Mexican-Americansaregeneticallydiverse,witha
OPENACCESS highlyvariabledistributionofNativeAmerican,European,andAfricanancestries.Here,we
Citation:HuH,HuffCD,YamamuraY,WuX,Strom evaluatetheroleofNativeAmericanancestryonBMIanddiabetesriskinawell-defined
SS(2015)TheRelationshipbetweenNative Mexican-Americanpopulation.Participantswererandomlyselectedamongindividuals
AmericanAncestry,BodyMassIndexandDiabetes
residingintheHoustonareawhoareenrolledintheMexican-AmericanCohortstudy.Using
RiskamongMexican-Americans.PLoSONE10(10):
acustomIlluminaGoldenGatePanel,wegenotypedDNAfrom4,662cohortparticipantsfor
e0141260.doi:10.1371/journal.pone.0141260
87Ancestry-InformativeMarkers.Onaverage,theparticipantswereof50.2%NativeAmeri-
Editor:TarasKOleksyk,UniverityofPuertoRicoat
canancestry,42.7%Europeanancestryand7.1%Africanancestry.Usingmultivariatelin-
Mayaguez,UNITEDSTATES
earregression,wefoundBMIandNativeAmericanancestrywereinverselycorrelated;
Received:June19,2015
individualswith<20%NativeAmericanancestrywere2.5timesmorelikelytobeseverely
Accepted:October5,2015 obesecomparedtothosewith>80%NativeAmericanancestry.Furthermore,wedemon-
Published:October26,2015 stratedaninteractionbetweenBMIandNativeAmericanancestryindiabetesriskamong
Copyright:©2015Huetal.Thisisanopenaccess women;NativeAmericanancestrywasastrongriskfactorfordiabetesonlyamongover-
articledistributedunderthetermsoftheCreative weightandobesewomen(OR=1.190foreach10%increaseinNativeAmericanancestry).
CommonsAttributionLicense,whichpermits
Thisstudyoffersnewinsightintothecomplexrelationshipbetweenobesity,geneticances-
unrestricteduse,distribution,andreproductioninany
try,andtheirrespectiveeffectsondiabetesrisk.Findingsfromthisstudymayimprovethe
medium,providedtheoriginalauthorandsourceare
credited. diabetesriskpredictionamongMexican-Americanindividualstherebyfacilitatingtargeted
preventionstrategies.
DataAvailabilityStatement:Dataunderlyingthe
analysesarewithinthepaperanditsSupporting
Informationfiles.
Funding:TheCohortreceivesfundscollected
pursuanttotheComprehensiveTobaccoSettlement
Introduction
of1998andappropriatedbythe76thlegislatureto
TheUniversityofTexasMDAndersonCancer TheMexican-Americanpopulationisageneticallydiverseethnicgroupwithvaryingpropor-
Center,fromtheCarolineWLawFundforCancer
tionsofNativeAmerican,EuropeanandAfricanancestry.Comparedtonon-HispanicEuro-
Prevention,andtheDanDuncanFamilyInstitutefor
peanAmericans,NativeAmericansandHispanicAmericanshavehigherBodyMassIndex
RiskAssessmentandCancerPrevention.HaoHuis
(BMI),increasedratesofobesity,andhigherincidenceoftype2diabetes[1–4].Theincreased
supportedbyTheUniversityofTexasMDAnderson
CancerCenterOdysseyfellowship.Thefundershad ratesofobesityandtype2diabetesamongthesepopulationsisdueinparttoshared
PLOSONE|DOI:10.1371/journal.pone.0141260 October26,2015 1/13
NativeAmericanAncestry,Obesity,andDiabetesinHispanics
noroleinstudydesign,datacollectionandanalysis, environmentalriskfactorssuchaslowersocio-economicalstatusanddietcomposition[5–7],
decisiontopublish,orpreparationofthemanuscript. butsharedgeneticriskfactorsmayalsobeacontributingfactor[8–10].
CompetingInterests:Theauthorshavedeclared Thestrongcorrelationbetweentype2diabetesandobesity[11]motivatesthehypothesis
thatnocompetinginterestsexist. thatNativeAmericangeneticancestryispositivelyassociatedwithbothBMIandtype2diabe-
tesrisk.However,recentstudiessuggestthatthisrelationshipbetweenNativeAmericanances-
try,BMI,andtype2diabetesisfarmorecomplex.Astudyconductedin170Hispanic,Native
Americanandmixed-ethnicitystudentsinNewMexicosuggestedthatnon-Europeangenetic
ancestrywaspositivelycorrelatedwithBMI(p=0.008)[2].Similarly,asecondstudyof846
NativeAmericanparticipantsrecruitedfrom8NativeAmericanreservationsreportedasignif-
icantpositivecorrelation(p=1.46e-4)[12],Incontrast,astudyinvolving1,506Mexican
AmericansfromStarrCounty,TexasfoundanegativecorrelationbetweenNativeAmerican
ancestryandBMI(p=0.011)[13].Eachofthesestudiesusedgeneticmarkerstoestimateindi-
vidualancestryandeachcontrolledforsocio-economicstatus.InasampleofLatinopopula-
tionscontaining662type2diabetescasesand269controlsfromcentralMexicoand
Colombia,researchers[6]estimatedtheamountofEuropeangeneticancestrybygenotyping
67ancestryinformativemarkers(AIM)amongparticipants.Theyfoundthatnon-European
ancestrywaspositivelycorrelatedwithtype2diabetesrisk(oddsratioof16.7and3.8fora
100%increaseinnon-EuropeanancestryinMexicansandColombians,respectively).How-
ever,aftercontrollingforsocioeconomicstatus,theassociationbetweenancestryandtype2
diabeteswasmuchweakerinsamplesfromcentralMexico(oddsratioof6.0,p=0.02)and
non-significantinsamplesfromColombia.Anotherstudy[14]conductedon286type2diabe-
tespatientsand275controlsfromMexicoCityfoundasimilartrend:theoddsratiofordiabe-
tesassociatedwitha100%increaseinNativeAmericanadmixturewas1.6,however,thisresult
wasnotstatisticallysignificant.Together,theseresultssuggestthatNativeAmericanancestry
mayincreasetype2diabetesrisk,butthattheinfluenceofNativeAmericanancestryonBMI
valuesdependsonthespecificpopulationandtheenvironment.Giventhecomplexrelation-
shipamonggeneticancestry,BMI,anddiabetesrisk,wehypothesizethatNativeAmerican
ancestryandBMIinfluencetheriskofdiabetesinanon-independentmanner.Althoughsome
evidenceexistsforaninteractionbetweenBMIandself-reportedAfricanancestryindiabetes
risk[15],nosuchinteractionhasbeenreportedinMexican-Americans.
Ultimately,anydirectrelationshipbetweenNativeAmericanancestry,diabetesrisk,and
BMIshouldbetheresultofindividualriskvariantsthataremorecommoninpopulationswith
NativeAmericanancestry.Genome-WideAssociationStudies(GWAS)haveidentifiedover50
locisignificantlyassociatedwithdiabetesandover30locisignificantlyassociatedwithBMI
[16];atleast14[9,17–19]and10[8,20]ofthemhavebeenreplicatedinHispanicpopulations.
StudiesinMexicanpopulationshavealsoidentifiedadditionalrisklociofdiabetes.In2006,
onestudyonasingleMexican-Americanfamily[21]foundanoveldiabetesriskmutationin
ADRB3usinglinkageanalysis;morerecently,aGWASstudyconductedonMexican-Ameri-
cansinStarrCounty,Texas[9]foundthreenovelriskgenes,TOMM7,HNTandPARD3B.
However,itislargelyunknownhowmuchpopulationheterogeneityindiabetesprevalencecan
beexplainedbytheseloci.Encouragingprogresseshavebeenmadeina2013GWASstudyin
LatinAmericansinvolving3,848type2diabetescasesand4,366controls[10].Ariskhaplotype
inSLC16A11wasfoundtobeverycommonamongNativeAmericansandMexicanAmericans
butrareinEuropeansandAfricans;thishaplotypeaccountsfor20%ofthedifferenceintype2
diabetesprevalencebetweenMexican-AmericansandEuropeans.However,mostofthe
increasedriskoftype2diabetesinMexicanAmericansremainsunexplained.
Tofurtherinvestigatetherelationshipbetweengeneticancestry,BMI,anddiabetesrisk
amongMexicanAmericans,wegenotypedAncestry-InformativeMarkers(AIMs)in4,662
MexicanAmericanparticipantslivinginHouston,Texas.Weestimatethegeneticancestryof
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Table1. Demographiccharacteristicsofparticipants.
Men(n=1273) Women(n=3389) p-value*
Mean SD Mean SD
Age 40.1 16.8 39.2 14.5 0.163
BMI 29.6 6.1 30.9 7.3 1.41E-06
Overweight(BMIbetween25and30) 477(37.5%) - 1011(29.8%) - 7.81E-07
Obesity(BMI>=30.0) 525(41.2%) - 1661(49.0%) - 2.43E-06
HBP 203(15.9%) - 595(17.6%) - 2.06E-01
Diabetes 146(11.5%) - 445(13.1%) - 1.38E-01
*p-valuesarecalculatedwithWilcoxonranksumtestforageandBMI,andwithFisherexacttestotherwise.
doi:10.1371/journal.pone.0141260.t001
eachindividualusingADMIXTURE[22]andthenevaluatetherelationshipbetweengenetic
ancestry,BMI,anddiabetesriskinthispopulation.
Results
Estimatinggeneticancestry
WesummarizedthedemographiccharacteristicsoftheparticipantsofthisstudyinTable1,
andtheinformationofthe87AIMsinS1Table.WefirstusedthetoolADMIXTURE[22]to
generategeneticancestryestimatesforeachindividual.ADMIXTUREisamodel-basedclus-
teringalgorithmforestimatingindividualgeneticancestry;itusesthesamelikelihoodmodel
asinitspredecessorSTRUCTURE[23]butissubstantiallyfaster[22].Acommonlyused
approachforestimatinggeneticancestrywithmodel-basedmethodsistocalculatethegeno-
typefrequenciesinthe“source”populationsusingareferencepopulationpanel.[24]However,
wedidnothaveaccesstoNativeAmericanDNAsamplesorpublicallyavailableNativeAmeri-
cangenotypedataonall87AIMs.Nonetheless,becausethelikelihoodmodelofADMIXTURE
assumesthatallinputmarkersareinlinkageequilibrium,[22]onlytheallelefrequencyateach
individualmarkerareneededtoestimategeneticancestry.Therefore,wegeneratedthegeno-
typesof87AIMsin3000simulatedindividualsofAfrican,EuropeansandNativeAmerican
ancestries,accordingtopreviouslyreportedallelefrequencies.Wethenpredictedtheancestry
proportionsofourparticipantswithasupervised-learningstrategyusingADMIXTURE.
Onaverage,ourparticipantswereof7.1%Africanancestry,50.2%NativeAmericanances-
tryand42.7%Europeanancestry(Fig1).ThevariationinAfricanancestrybetweenindividuals
wasrelativesmall(SD=0.062)comparedtoEuropeanandNativeAmericanancestries
(SD=0.168and0.164,respectively).Thecompositionofgeneticancestrywasverysimilar
betweenmenandwomen(Table2).Inordertovalidatethegeneticancestryestimate,wealso
performedaseparateADMIXTURErunandincludedEuropeanandAfricanindividualsfrom
1000GenomesProjectsintheanalysis.Ourmodelcorrectlypredictedtheethnicitiesofthese
individualswithhighaccuracies(S2Table).
CorrelationbetweengeneticancestryandBMI
WenextevaluatedtheassociationofgeneticancestrywithBMIusingmultivariatelinearregres-
sion.Overall,a10%increaseinNativeAmericanancestryreducedBMIby0.13m/kg2(Table3).
However,theassociationwasonlysignificantamongwomen,whichprobablyresultedfromthe
smallersamplesizeinmen(n=1272)versuswomen(n=3387).Consistentwiththisexplana-
tion,theconfidenceintervaloftheregressioncoefficientoverlappedbetweenmenandwomen,
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Fig1.Geneticancestriesof4,659participantsintheMexican-AmericanCohort.Eachcolumnrepresentsoneindividual.Thelengthsoflineswith
differentcolorsineachcolumnrepresenttheproportionofgeneticancestryforthisindividual.Green:European;Blue:NativeAmerican;Red:African.
doi:10.1371/journal.pone.0141260.g001
andtheinteractiontermbetweenNativeAmericanancestryandgenderwasnotsignificant
(p>0.1).Additionally,apoweranalysisindicatedthatthestatisticalpowertodetectasignificant
effectofNativeAmericanancestryinmenisonly25%assumingthattheeffectsizeisthesameas
inwomen.(MaterialsandMethods).AfricanancestryisalsosignificantlycorrelatedwithBMI,
witha10%increaseinAfricanancestryincreasingBMIby0.43m/kg2.Wenextcomparedthe
BMIdistributionsbetweenindividualswithlessthan20%NativeAmericanancestry(n=195)
andwithgreaterthan80%NativeAmericanancestry(n=155)(Fig2)andfoundthatthelatter
grouphadsignificantlylowerBMIthantheformer(p-value=3.7×10−4fromWilcoxontest),
withmeanBMIof29.2and31.9,respectively.Remarkably,30.3%oftheindividualsfromthe
Table2. Geneticancestrybygender.
Men Women p-value*
Mean SD Mean SD
African 6.91% 6.21% 7.12% 6.23% 0.28
Europeans 43.20% 16.89% 42.50% 16.79% 0.22
NativeAmerican 49.90% 16.62% 50.38% 16.37% 0.36
*p-valuesarecalculatedwithWilcoxonranksumtest.
doi:10.1371/journal.pone.0141260.t002
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Table3. AssociationbetweengeneticancestryandBMI.
NativeAmericanAncestry AfricanAncestry
Regressioncoefficient* p-value Regressioncoefficient* p-value
Male -0.29(-2.32,1.74) 0.78 1.62(-3.69,6.92) 0.55
Female -1.6(-3.15,-0.05) 0.042 5.44(1.49,9.4) 0.0071
Combined -1.34(-2.60,-0.07) 0.038 4.31(1.05,7.57) 0.01
*Shownintheparenthesesarethe95%confidenceintervaloftheregressioncoefficient
doi:10.1371/journal.pone.0141260.t003
groupwithlessthan20%NativeAmericanancestrywereseverelyobese(BMI>=35)compared
to12.3%inthegroupwithgreaterthan80%NativeAmericanancestry(p=5.6×10−5fromFisher
exacttest).
Associationbetweengeneticancestry,BMIanddiabetesstatus
Weevaluatedself-reporteddiabetesstatustoinvestigatetheinfluenceofNativeAmerican
ancestryondiabetesriskinMexican-Americans.WhenBMIwasnotincludedasacovariate,
wefoundthatNativeAmericanancestrywasasignificantriskfactorfordiabetes,withanOR
of1.067fora10%increaseinNativeAmericanancestry(p=0.037;Table4),whichisconsis-
tentwithpreviousestimatewithinAmericanIndianandAlaskaNativeadults[25].
Fig2.HistogramofBMIvaluesinhigh-NativeAmericanAncestrygroup(grey;NAancestry>80%)andlow-NativeAmericanAncestrygroup
(black;NAancestry<20%).
doi:10.1371/journal.pone.0141260.g002
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Table4. RegressionanalysisofdiabetesstatuswithNativeAmericangeneticancestry.
NotcontrollingforBMI ControllingforBMI
ORassociatedwith10%increaseinNA p- ORassociatedwith10%increaseinNA p-
ancestry* value ancestry* value
Male 0.987(0.871,1.120) 0.84 Male 0.986(0.869,1.118) 0.82
Female 1.097(1.023,1.177) 0.0098 Female 1.108(1.032,1.19) 0.0045
Combined 1.067(1.004,1.135) 0.037 Combined 1.077(1.012,1.145) 0.019
*Shownintheparenthesesarethe95%confidenceintervals
doi:10.1371/journal.pone.0141260.t004
Interestingly,aftercontrollingforBMI,theassociationbetweenNativeAmericanancestryand
diabetesbecamestronger(OR=1.077fora10%increaseinNativeAmericanancestry;
p=0.019).CombiningthiswiththeobservationthatBMIissignificantlylowerinMexican-
AmericansofhighNativeAmericanancestry,weconcludedthatNativeAmericanancestry
increasesthediabetesriskdespiteitsinverseassociationwithBMI.Whenwestratifiedthese
databygender,wefoundthattheassociationbetweenNativeAmericanancestryanddiabetes
wasonlysignificantamongwomen(Table4),whichonceagainwaslikelyduetothesmaller
samplesizeofmen.The95%confidenceintervaloftheORfora10%increaseinNativeAmeri-
canancestrywas0.869to1.118inmen,andthustheresultsareconsistentwiththeeffectsize
weobservedinwomen.WealsoobservednoevidenceofaNativeAmericanancestryxgender
interaction(p=0.08).Inaddition,apoweranalysissuggestedthatthestatisticalpowerto
detectasignificanteffectofNativeAmericanancestryinmenisonly38%assumingthatthe
effectsizeisthesameasinwomen.(MaterialsandMethods)
WenextinvestigatedwhetherthemagnitudeofriskassociatedwithNativeAmericanances-
trydiffersbyBMIlevel.Toaddressthisissue,westratifiedthedataintofourBMIgroupsbased
ontheclinicalguidelinesoftheNationalHeart,Lung,andBloodInstitute,[26]asshownin
Table5.WeanalyzedtheassociationbetweenNativeAmericanancestryanddiabetesforeach
groupusingmultivariatelogisticregression,aftercontrollingfordailyexercise,age,highblood
pressure,andacculturationscore.Duetothelimitedsamplesizeandpowerinmen(Table4),
werestrictedouranalysestoonlywomen.Surprisingly,wefoundthatNativeAmericanances-
trywasonlysignificantlyassociatedwithdiabetesriskamongoverweightandobesewomen
(BMIbetween25and35),withanORof1.190fora10%increaseinNativeAmericanancestry
(p=0.0004;Table5).TherewasnoassociationbetweenNativeAmericanancestryanddiabetes
riskamongseverelyobese(BMI>=35)andnormal/under-weight(BMI<25)women
(p=0.59and0.66;OR=1.033and0.951,respectively).Wealsoperformedalikelihoodratio
testforinteractionbetweentheNativeAmericangeneticancestryandBMI,whichwas
Table5. RegressingNativeAmericangeneticancestrywithdiabetesriskbyBMIinwomen.
Samplesize OddsratiorelativetoBMI<25group* ORassociatedwith10%increaseinNAancestry* p-value
BMI<25 689 1(1,1) 0.951(0.759,1.191) 0.6614
BMI>=25and<35 1871 2.248(1.594,3.172) 1.190(1.08,1.311) 0.0004
BMI>=25and<30 1011 1.930(1.329,2.801) 1.254(1.081,1.456) 0.0029
BMI>=30and<35 860 2.638(1.824,3.814) 1.132(0.993,1.29) 0.0641
BMI>=35 800 4.233(2.958,6.058) 1.033(0.917,1.163) 0.594
All 3360 - 1.097(1.023,1.177) 0.0098
*Shownintheparenthesesarethe95%confidenceintervals
doi:10.1371/journal.pone.0141260.t005
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NativeAmericanAncestry,Obesity,andDiabetesinHispanics
significantatp=0.049(SeeMaterialsandMethods).TheseresultssuggestthatNativeAmeri-
canancestryhasdifferentialeffectsondiabetesriskamongdifferentBMIgroups.
Discussion
Inthisstudy,weidentifiedaninverseassociationbetweenBMIandNativeAmericanancestry
intheMexicanAmericanpopulationinHouston,Texas.Incontrast,threepreviousstudies[1,
3,12]reportedpositivecorrelationsintheCreepopulation(n=402),PimaIndians(n=7,796)
andaNativeAmericanCommunity(n=846).Thismaysuggestaninteractionbetweenlife-
style,socioeconomicenvironment,andgeneticancestry,possiblyspecifictoMexicanAmeri-
cans.Forexample,ourparticipantsresideinahighlyurbanizedareaofHouston,Texas,in
contrasttotheindigenousAmerindiancommunityenvironmentinthepublisheddata;thedif-
ferencesinthelifestylesacrossthesepopulationsmaycontributetothedifferentdirectionsof
association.Interestingly,onestudy[13]conductedontheMexicanAmericanpopulationin
StarrCounty,Texas(n=1,506)observedthesameinverseassociationbetweenBMIandNative
Americanancestryasourstudy,whiletwootheradmixedpopulationstudies[6,24]onnative
Mexicans(n=931)andPuertoRicanslivinginBoston(n=1129)didnotidentifyasignificant
association.Duetoourlargesamplesize(4,662)andthehomogenousculturalbackgroundof
ourparticipants,ourstudywasmorepowerfultodetectassociationsinthisadmixedpopula-
tionthanpreviousstudies.Analternativeexplanation,however,isthattheinverseassociation
betweenBMIandNativeAmericanancestryonlyexistsinMexican-Americanpopulations.
GiventhecomplexrelationshipbetweenNativeAmericanancestryanddiabetesrisk,diabetes
riskpredictionmodelsinpopulationswithNativeAmericanancestryshouldbecarefullycali-
bratedinthetargetpopulations.
OnepossibleconfounderintheanalysisofBMIisdiet.High-calorieWesterndietcharacter-
izedbyhighamountsofredmeats,high-fatdietaryproductsandrefinedgrainsarereportedly
positivelycorrelatedwiththelevelsofleptin[27];therefore,ifNativeAmericanancestryiscor-
relatedwiththedietpattern,thentheassociationsbetweenBMIandNativeAmericanancestry
maybeconfounded.Totestthishypothesis,weanalyzedasubsetof2,515respondentswho
hasbeenaskedtoranktheirdietfrom1to5,with1being“onlyMexicanfoods”and5being
“onlyAmericanfoods”.WefoundthatthepercentageofNativeAmericanancestryweresimi-
laracrossindividualswithdifferentdietarypatterns(S1Fig;r2betweenNativeAmerican
ancestryanddietarypatternis0.0086).Also,whenweaddeddietarypatterntotheregression
modelofBMI,thecoefficientofdietarypatternwasnotsignificant(0.06(-0.31,0.43);p=0.74).
Theseevidencessuggestthatdietisunlikelyaconfounderinouranalyses.
OurresultssuggestthatNativeAmericanancestrymayonlybeanimportantriskfactorfor
diabetesamongoverweightandmoderatelyobeseindividuals.WehypothesizethattheNative
AmericanancestryinteractswithBMIondiabetesriskinindividualswithBMIlessthan35,
whereasthealteredhormonalmilieuassociatedwithsevereobesitymayhaveanover-arching
influenceondiabetesrelativetotheeffectsassociatedwithNativeAmericanancestry.Interest-
ingly,apreviousstudy[1]hadasimilarobservationintheCreepopulation,butontheriskof
gestationaldiabetesmellitus.Specifically,normalweightCreewomen((cid:1)77kg)haveasimilar
riskofgestationaldiabetesmellitusasnon-Nativeswomen,butoverweightCree(>77kg)
womenweremorethantwiceaslikelytohavegestationaldiabetescomparedtoobesenon-
Nativewhites.ConsideringthesharedetiologybetweengestationaldiabetesandtypeIIdiabe-
tes[28],itislikelythatthesamemechanismcausestheinteractionbetweenBMIandgenetic
ancestryinbothdiseases.Analternativeexplanationisthat,becausegestationaldiabetesisalso
ariskfactoroftypeIIdiabetes[29],theinteractiontermbetweenBMIandgeneticancestryin
ourmodelisaconfounderofthetrueassociationbetweengestationaldiabetesanddiabetes.If
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thisistrue,thentheoddsratiooftheinteractiontermingestationaldiabetesshouldbemuch
largerthanindiabetes.However,thisisnotthecasewhenwecompare[1]toourstudy(odds
ratioof1.45fortheethnicity×BMItermintheirworkand5.44fortheethnicity×obesityterm
inourwork),suggestingthelatterexplanationunlikely.
Inouranalysis,theNativeAmericanancestrywasassociatedwithincreasedBMIand
decreasedriskofdiabetesonlyamongwomenbutnotinmen.Weattributethisobservationto
themuchlargersamplesizeinwomencomparedtomen(2.66fold),ratherthanarealdiffer-
enceacrossthetwosexes,forthreereasons.First,theconfidenceintervalsoftheregression
coefficientsareoverlappingbetweenmenandwomenforbothanalyses.Second,thepower
analysessuggestedthatifwereducedthesamplesizeofthewomentothesameasmen,then
weonlyhave25%and38%powertodetectasignificantassociationofNativeAmericanances-
trywithBMIanddiabetes,respectively.Lastly,aformalZ-testbasedontheregressioncoeffi-
cientsandtheirstandarderrors[30]oftheNativeAmericanancestrygeneratedap-valueof
0.32inBMIanalysisand0.11indiabetesanalysis,underthenullhypothesisthattheeffect
sizesinmenandwomenarethesame.Therefore,weconcludedthatthereisnoevidenceto
supportasex-differenceintheriskofBMIanddiabetesassociatedwithNativeAmerican
ancestry.
Themainstrengthsofthisstudyareitslargesamplesize(n=4,662)andthehomogenous
culturalbackgroundofourparticipants.TheparticipantsarefrominnercityHouston,there-
forereducingvariationinenvironmentalfactorsandincreasingstatisticalpowertoidentify
geneticassociations.Theuseofgeneticadmixtureforeachindividualratherthanusingself-
identificationofacomplexgeneticidentityisanotherstrength.Wealsopointoutthreelimita-
tionsofthisresearch.First,allcasesofdiabeteswereself-reportedandtheinformationonthe
typeofdiabeteswasnotavailable.Second,informationregardingtheageofonsetwasunavail-
able.Therefore,weusedtheageatthetimeofinterviewasasurrogatefortheageofonsetdur-
ingouranalyses.Third,becauseofthehighcollinearitybetweenNativeAmericanand
Europeanancestry,wecannotruleoutthepossibilitythattheassociationsbetweenBMI,diabe-
tes,andNativeAmericanancestryweredrivenbyassociationsbetweenBMI,diabetes,and
Europeanancestryintheoppositedirection.Todistinguishbetweenthesetwopossibilities,an
independentassociationstudyinapopulationwithoutsuchhighcollinearitybetweenNative
AmericanandEuropeanancestryiswarranted.
Insummary,westudiedaMexicanAmericanpopulationinHouston,Texasandexplored
thecorrelationamongNativeAmericanancestry,BMI,anddiabetesrisk.Interestingly,we
foundthatNativeAmericanancestrywasassociatedwithdecreasedBMIbutincreaseddiabetes
risk.TheincreasedriskofNativeAmericanancestryfordiabetesismostpronouncedinover-
weightandobeseindividualsbutnotsignificantamongnormalandseverelyoverweight
groups,suggestinganinteractioneffectbetweenBMIandNativeAmericanancestry.Future
studiesarerequiredtoreplicatethisfindingand,ifreplicated,torevealtheexactmechanismof
differentialrisk.Thefindingsfromthisstudywillimproveeffortstopredictdiabetesrisk
amongMexican-Americanindividualsandfacilitatethedesignofmoreeffectivediabetespre-
ventionstrategies.
MaterialsandMethods
Studypopulationandsamplecollection
ThestudywasapprovedbytheinstitutionalreviewboardatM.D.AndersonCancerCenter
andallparticipantshavesignedawrittenconsentformaspertheDeclarationofHelsinki.We
randomlyselected4,662individualswhowereparticipantsoftheMexicanAmericanCohort,a
prospectivelongitudinalstudyofresidentsofHouston,Texaswhichbeenpreviouslydescribed.
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[31]Participantswerefromaculturallyhomogeneousbutgeneticallydiversepopulation,mak-
ingitsuitedforstudyingthegeneticepidemiologyofinheriteddiseases.Wecollecteddemo-
graphic,lifestyle,andmedicalandfamilyhistorydataaswellasbiologicalspecimensfrom
participantsatbaselineenrollment.Themajoritywerewomen(72.7%).Incomparisonto
women,menreportedlowerBMIonaverage(29.6vs.30.9,p=1.41x10-6fromWilcoxonrank
sumtest),andlowerratesofobesity(definedasBMI>30;41.2%vs.49.0%,p=2.4x10-6from
Fisherexacttest).Theratesofhighbloodpressureanddiabetesweresimilarbetweenmenand
women.
DNAgenotypingandgeneticancestryestimate
Weinitiallyselected96Ancestry-InformativeMarkers(AIMs)thathavelargeallelefrequency
differencesamongNativeAmericans,EuropeansandAfricans,fromthreedifferentstudieson
Mexicanpopulations[6,14,32].WeincludedalltheAIMsusedinthefirsttwostudies[6,14],
andacomplementarysetof15AIMsfromthethirdstudy[32].WeusedIlluminaGoldenGate
Paneltoperformthegenotyping.BecauseAIMswithinhighlyadmixedpopulationsoftendevi-
atefromHardyWeinbergEquilibrium(HWE),[33,34]weappliedalooseHWEfilterof
p>5x10-8.Ofthe96markers,3markershadmorethan5%missinggenotypingrate;3were
reportedasfailedcallsbytheGoldenGatepipeline;2weresmallinsertionsordeletions(indels);
1didnotpasstheHWEfilter(S1Table).Thesemarkerswereexcludedfromfurtheranalyses.
Weremovedindelsbecausewecouldnotreliablyestimateallelefrequenciesfrompublic
sequencingdata.Intotal,87markersremained.Threeindividualsinourdatawithgreaterthan
5%missing-genotyperatewereremovedfromthestudy.
Priortothegeneticancestrycalculation,wefirstestimatedtheallelefrequenciesofthe87
AIMsinAfrican(YorubapopulationinIbadan,Nigeria)andEuropean(Utahresidentswith
NorthernandWesternEuropeanancestry)populationsbasedonthepublicallyavailable
genomesfrom1000GenomeProject.[35]ForthefrequenciesoftheselectedAIMsamong
NativeAmericans,weusedthereportedallelefrequencies[6,14,32]wheneverpossible;other-
wise,weusedtheallelefrequencyestimatesintheTotonacpopulation.[36]The87AIMswere
allseparatedbyatleast600kb,andthemeanandstandarddeviationofr2valuebetweenany
twoAIMsonthesamechromosomewas0.08and0.09inthe1000GenomesProject.[35]We
thensimulatedgenotypesforthe87AIMsin1000individualsfromeachofthethreepopula-
tions(African,Europeans,andNativeAmericans)undertheassumptionthatallmarkerswere
inlinkageequilibrium.Finally,weranADMIXTURE[22]onthedatasetcontainingallsimu-
latedandgenotypedindividuals,settingKto3andthegeneticancestryofthesimulatedindi-
vidualsto100%ofthecorrespondingpopulation.TheADMIXTURE-predictedancestry
proportionsofourgenotypedsampleswereusedasthegeneticancestryestimate.Welistedthe
geneticancestryestimate,diabetesstatus,BMIandothercovariatesforeachindividualinS3
Table.
Statisticalanalyses
WeusedmultivariatelinearregressionstoexaminetheassociationsbetweenBMIandgenetic
ancestry.WeincludedthefollowingcovariatesthatweresignificantlyassociatedwithBMIin
ourstudy:dailyexercise,age,acculturationscore,educationallevel,percentagelifetimespent
inU.S,alcoholconsumption,smokinghistoryandAfricanancestry.Wealsoincludededuca-
tionallevelinthemodelbecauseofthedocumentedcorrelationsbetweeneducationalleveland
BMI[37].TheDailyexercisecovariateisabinaryvariableindicatingwhethertheparticipant
performs150minutesofmoderate-intensityactivityor75minutesvigorous-intensityactivity
eachweek.Levelofacculturationwasassessedwith4items(languageuse,linguistic
PLOSONE|DOI:10.1371/journal.pone.0141260 October26,2015 9/13
NativeAmericanAncestry,Obesity,andDiabetesinHispanics
proficiency,TVusageandradiousage)fromtheBidimensionalAcculturationScaleforHis-
panics,avalidatedinstrumentthathasverygoodinternalconsistency(Cronbach's
alpha=0.87)andwasdesignedforusewithMexicanAmericans[38].TheEducationallevel
covariateisabinaryvariableindicatingwhethertheparticipanthadatleasthigh-schoollevel
educationortechnicaltraining.Thesmokinghistorycovariateisafactorthatcanbe"never
smoker","pastsmoker"or"currentsmoker".Thealcoholconsumptioncovariatewascreatedin
asimilarfashion.ThecorrelationbetweenAfricanandNativeAmericanancestrieswasvery
low(r2=0.016),whichjustifiestheinclusionofbothancestryestimatesinthesamemodel.We
didnotincludeEuropeanancestryasacovariateduetoitscollinearitywithNativeAmerican
ancestry(r2=0.87).
Toanalyzetheassociationbetweendiabetesandgeneticancestry,weusedmultivariate
logisticregressions,controllingforthefollowingcovariatesthatweresignificantlyassociated
withdiabetesinourstudy:dailyexercise,age,andhighbloodpressurestatus.Wealsoincluded
acculturationscorebecauseofthereportedassociationbetweenacculturationscoreanddiabe-
tes.[39]WeperformedtheanalysisbothwithandwithouttheBMIcovariate,asindicatedin
theResultssection.Fortheanalysesinvolvingmen,wealsoincludedalcoholconsumptionand
smokinghistory,becausetheyweresignificantlyassociatedwithdiabetes.
Poweranalysis
WehavefoundthattheassociationsbetweenNativeAmericanancestry,BMI,anddiabetes
wereonlysignificantinwomenbutnotinmen.Toinvestigatewhetherthiswasduetothe
smallersamplesizeofmen(n=1272)comparedtowomen(n=3387),weperformedthefol-
lowingpoweranalysis.Werandomlysampled1272individualsamong3387womenwith
replacement,andonthissubsetofwomenconstructedthemultivariatelinear(forBMIanaly-
sis)orlogistic(fordiabetesanalysis)regressionmodelsinthesamewayasintheoriginalanaly-
ses.Werepeatedthisprocess500times,andrecordedwhatproportionofthere-sampled
modelsreportedasignificantp-valueforNativeAmericanancestry.Weusedthisproportion
astheestimateofpowerfordetectingasignificantassociationamongmen,assumingtheeffect
sizeishomogenousbetweenmenandwomen.
TestingtheinteractionsbetweengeneticancestryandBMIindiabetes
risk
InordertoevaluatetheinteractioneffectbetweengeneticancestryandBMI,wefirstcatego-
rizedBMIintofourgroups:1)normalweight(BMI<25),2)overweight(BMIbetween25and
30),3)obese(BMIbetween30and35),and4)severelyobese(BMI>35).Wecalculatedthe
relativeriskofdiabetesforeachBMIgroupusinglogisticregression,accountingfordailyexer-
cise,age,highbloodpressure,andacculturationscores.Twoneighboringgroups(overweight
andobese)havesimilarrelativerisksandtheir95%confidenceintervalsoverlapwitheach
other.Waldtestssuggestedthattherelativerisksofthesetwogroupsarenotsignificantlydif-
ferent(p=0.30),whileforanyothercombinationsitwasalwayssignificant.Therefore,we
revisedourmodeltomergetheoverweightandobeseparticipantsintooneriskgroup.We
thenaddedinteractiontermsbetweengeneticancestriesandcategoricalBMIvalues.This
addedtwodegreesoffreedomintothepreviousmodel;asaresult,underthenullhypothesisof
nointeraction,thevalueof-2timestheloglikelihooddifferencebetweenthesetwomodels
shouldbechi-squaredistributedwith2degreesoffreedom.Thisallowedustotestwhetherthe
interactiontermissignificant.
PLOSONE|DOI:10.1371/journal.pone.0141260 October26,2015 10/13