Genome-wide analyses of aggressiveness in attention-deficit hyperactivity disorder

15 Pages·2016·2.38 MB·English

RESEARCH ARTICLE
Neuropsychiatric Genetics
Genome-Wide Analyses of Aggressiveness
in Attention-Deficit Hyperactivity Disorder
Erlend J. Brevik,1,2,3* Marjolein M. J. van Donkelaar,4 Heike Weber,5 Cristina S(cid:1)anchez-Mora,6,7,8
Christian Jacob,9 Olga Rivero,10 Sarah Kittel-Schneider,10 Iris Garcia-Mart´ınez,6,7 Marcel Aebi,11,12
Kimm van Hulzen,4 Bru Cormand,13,14,15 Josep A. Ramos-Quiroga,6,7,8,16 IMAGE Consortium,
Klaus-Peter Lesch,9,17 Andreas Reif,5 Marta Ribas(cid:1)es,6,7,8 Barbara Franke,4,18 Maj-Britt Posserud,1,2
Stefan Johansson,19,20 Astri J. Lundervold,2,3 Jan Haavik,1,2 and Tetyana Zayats2*
1Division of Psychiatry, Haukeland University Hospital, Bergen, Norway
2K.G. JebsenCentrefor Research onNeuropsychiatricDisorders, Departmentof Biomedicine, Universityof Bergen, Bergen, Norway
3Department ofBiological andMedicalPsychology, University of Bergen, Bergen, Norway
4Department ofHumanGenetics, Donders Institute for Brain, Cognition andBehaviour, Radboud University MedicalCenter, Nijmegen,
The Netherlands
5Department ofPsychiatry,Psychosomatics and Psychotherapy, University of Frankfurt, Frankfurt, Germany
6PsychiatricGenetics Unit, Vall d’Hebron Research Institute (VHIR), Universitat Aut(cid:3)onoma de Barcelona, Barcelona, Spain
7Department ofPsychiatry,Hospital Universitari Vall d’Hebron, Barcelona,Spain
8Biomedical Network Research Centre onMentalHealth (CIBERSAM), Barcelona, Spain
9Department ofPsychiatryandPsychotherapy,KlinikN€urtingen, N€urtingen,Germany
10Division of MolecularPsychiatry, Center of MentalHealth, University of W€urzburg, W€urzburg, Germany
11Department of Forensic Psychiatry,Childand Youth Forensic Service, UniversityHospital of Psychiatry,Zurich,Switzerland
12Department of Child andAdolescent Psychiatry, Universityof Zurich,Zurich, Switzerland
13Facultat deBiologia, Departament de Gen(cid:3)etica, Universitat de Barcelona, Catalonia, Spain
14Centrode Investigaci(cid:1)onBiom(cid:1)edica enRed de Enfermedades Raras (CIBERER), Barcelona, Spain
15Institutde Biomedicina de la Universitat de Barcelona (IBUB), Catalonia, Spain
16Department of Psychiatry and Legal Medicine, Universitat Aut(cid:3)onoma de Barcelona, Barcelona, Spain
17Department of Translational Neuroscience, School for Mental Health andNeuroscience (MHeNS),Maastricht University, Maastricht,
The Netherlands
18Department of Psychiatry,Donders Institute for Brain, Cognition and Behaviour,Radboud UniversityMedicalCenter, Nijmegen,
The Netherlands
19CenterforMedical Genetics andMolecularMedicine, Haukeland UniversityHospital, Bergen, Norway
20Department of ClinicalScience, Universityof Bergen, Bergen, Norway
ManuscriptReceived:23June2015;ManuscriptAccepted:9February2016
ThisisanopenaccessarticleunderthetermsoftheCreativeCommons Grant sponsor: Instituto de Salud Carlos III, Ministerio de Ciencia e
Attribution-NonCommercial License, which permits use, distribution Innovacio(cid:1)n, Spain; Grant sponsor: Instituto de Salud Carlos III-FIS,
andreproductioninanymedium,providedtheoriginalworkisproperly Spain;Grantnumbers:PI11/00571,PI11/01629,PI12/01139,PI14/01700;
citedand isnot usedfor commercial purposes. Grant sponsor: Ag(cid:3)encia de Gestio(cid:1) d’Ajuts Universitaris i de Recerca-
Grant sponsor: K.G. Jebsen Foundation for Medical Research; AGAUR Generalitat de Catalunya; Grant number: 2014SGR1357;
Grantsponsor:UniversityofBergen;Grantsponsor:WesternNorwegian Grantsponsor:DepartamentdeSalut,GovernmentofCatalonia,Spain;
HealthAuthorities(HelseVest);Grantsponsor:EuropeanCommunity’s Grant sponsor: NIH; Grant numbers: R01MH62873, R01MH081803;
Seventh Framework Programme; Grant number: FP7/2007–2013; Grant sponsor:European College ofNeuropsychopharmacology.
Grant sponsor: Research and Innovation Program; Grant numbers: (cid:1)Correspondence to:
602805,H2020;Grantsponsor:MarieSklodowska-Curie;Grantnumber: Erlend J. Brevik, PsyD, and Tetyana Zayats, M.D., Ph.D., K.G. Jebsen
643051 (MiND); Grant sponsor: Deutsche Forschungsgemeinschaft; Centre for Research on Neuropsychiatric Disorders, Department of
Grant numbers: DFG: KFO 125, TRR 58/A5, DFG RE1632/5-1; Biomedicine, University of Bergen,Bergen,Norway.
Grant sponsor: Fritz Thyssen Foundation; Grant number: E-mail: [email protected] (EJB);[email protected] (TZ)
Az.10.13.1185; Grant sponsor: Jacobs Foundation; Grant sponsor: Article first publishedonlinein WileyOnline Library
Spanish Ministerio de Economı´a y Competitividad; Grant number: (wileyonlinelibrary.com): 29March 2016
SAF2012-33484; Grant sponsor: AGAUR; Grant number: 2014SGR932; DOI10.1002/ajmg.b.32434
(cid:1) 2016 The Authors. American Journal of Medical Genetics Part B: Neuropsychiatric Genetics Published by Wiley Periodicals, Inc. 733
734 AMERICAN JOURNAL OF MEDICAL GENETICS PART B
Aggressivenessisabehavioraltraitthathasthepotentialtobe
harmful to individuals and society. With an estimated herita- How to Cite this Article:
bilityofabout40%,geneticsisimportantinitsdevelopment.We
Brevik EJ, van Donkelaar MMJ, Weber H,
performed an exploratory genome-wide association (GWA) S(cid:1)anchez-Mora C,Jacob C,Rivero O,Kittel-
analysisofchildhoodaggressivenessinattentiondeficithyper- Schneider S,Garcia-Martı´nez I, Aebi M,
activity disorder (ADHD) to gain insight into the underlying
van Hulzen K,Cormand B, Ramos-Quiroga
biological processes associated with this trait. Our primary
JA, IMAGE Consortium, Lesch K-P, Reif A,
sample consisted of 1,060 adult ADHD patients (aADHD). To Ribas(cid:1)esM, Franke B,Posserud M-B,
further explore the genetic architecture of childhood aggres-
Johansson S,Lundervold AJ, HaavikJ,
siveness, we performed enrichment analyses of suggestive
Zayats T.2016. Genome-Wide Analyses of
genome-wide associations observed in aADHD among GWA
Aggressiveness in Attention-Deficit
signals of dimensions of oppositionality (defiant/vindictive
Hyperactivity Disorder.
and irritable dimensions) in childhood ADHD (cADHD).
Am JMedGenet PartB 171B:733–747.
No single polymorphism reached genome-wide significance
(P<5.00E-08). The strongest signal in aADHD was observed
atrs10826548,withinalongnoncodingRNAgene(beta¼(cid:3)1.66,
standard error (SE)¼0.34, P¼1.07E-06), closely followed by
Thiscan beillustrated bythefact thataround 30%ofyouthand
rs35974940 in the neurotrimin gene (beta¼3.23, SE¼0.67,
25% of adult prison inmates are found to qualify for an ADHD
P¼1.26E-06).ThetopGWASNPsobservedinaADHDshowed
diagnosis[Youngetal.,2014].Studiesofchildhoodaggressiveness
significantenrichmentofsignalsfromboththedefiant/vindic-
in adults can, therefore, be of great importance to improve our
tive dimension (Fisher’s P-value¼2.28E-06) and the irritable
understanding of adult ADHD.
dimension in cADHD (Fisher’s P-value¼0.0061). In sum, our
The etiology of ADHD as well as traits of aggressiveness is
results identify a number of biologically interesting markers
complex,withgeneticsplayinganimportantrole.Theheritability
possibly underlying childhood aggressiveness and provide tar-
ofADHDhasbeenestimatedtobeupto88%acrossthelifespan
gets for further genetic exploration of aggressiveness across
[Larssonetal.,2013],whereastheestimatesofgeneticinfluenceon
psychiatric disorders. (cid:1)2016TheAuthors.AmericanJournalofMedical aggressionvaryacrossstudies,collectivelyreachingabout40–50%
GeneticsPartB:NeuropsychiatricGeneticsPublishedbyWileyPeriodicals,Inc. [Brendgenetal.,2006;TuvbladandBaker,2011].Suchdiversityin
theestimationofaggressionheritabilitymayresultfrominconsis-
Key words: ADHD; aggression; GWAS tency in measures across studies. Several different aggression
measureshavebeenutilizedtoassessthegeneticandenvironmen-
INTRODUCTION talinfluencesonitsdevelopment[Veroudeetal.,2015],reflecting
that there is no consensus regarding its definition [Ramirez and
Aggressivenesscanbedefinedasanybehaviordirectedtowardan Andreu, 2006]. Furthermore, the estimates of aggressiveness are
individualwiththeimmediateintenttocauseharm[Andersonand influenced by the age of the study participants. The literature
Bushman, 2002]. Violence, which is strongly related to aggres- reports stability of aggressiveness between childhood and adult-
siveness,isthesixthleadingcauseofburdenofdiseaseforpeople hood,withadolescenceasatransientperiodwithlittlestabilityin
aged 15–44 years worldwide [WHO, 2008]. To date, most inter- thistrait[Moffitt,2005].Genesseemtoexplainlittlevariationin
ventionsdesignedtoreduceviolencerisktypicallyhavesmalleffects, adolescent aggression, but are likely to account for individual
reflectingourlimitedunderstandingofitscausesandstressingthe differences in childhood and adult aggression [Lyons et al.,
needforfurtherstudies[Moffitt,2005;McGuire,2008]. 1995].Also,givenhigherlevelsofaggressioninmalesandhigher
Asacomplexphenomenon,aggressivenessspansacrossnumer- geneticloadinmaleswithantisocialbehaviorcomparedtofemales,
ousfacetsofhumanbehavior,rangingfromemotionallabilityand it is an open question whether genetic propensity is of greater
temperamental traits (e.g., hot-tempered, short fuse, irritable) to importance in one sex over the other [Miles and Carey, 1997;
physical violence [Lesch et al., 2012]. These traits are frequently TuvbladandBaker,2011].Interestingly,similarconsiderationsof
found among youth with attention deficit hyperactivity disorder ageandsexeffectsarealsopresentinstudiesofADHDaswellas
(ADHD), a common child and adolescent psychiatric disorder when ADHD is co-morbid with aggressive behavior [Faraone
with a prevalence of about 5% and a rate of persistence into et al., 1991, 2015].
adulthoodofabout50%[Faraoneetal.,2015].ADHDisdefined GiventhatADHDandaggressionoftenco-occurandthatboth
by symptoms of inattention and hyperactivity/impulsivity, and traitsareheritable,twinstudieshavenotedthepossibilityofshared
youthwithADHDoftenhaveco-existingdisorders,someofwhich genetic etiology between ADHD and aggression. A common
arecloselyrelatedtoaggressivenessandviolence,suchasconduct genetic factor has been reported among ADHD and symptoms
disorder (CD) and/or oppositional defiant disorder (ODD) and of aggression in 9–10-year-old children [Tuvblad et al., 2009].
disorders characterized by symptoms defined within the broader Likewise,ithasbeensuggestedthatimpulsivityandaggressionare
termofantisocialbehavior[Dalsgaardetal.,2002].Thesedisorders geneticallymediatedtoasimilarextent[Seroczynskietal.,1999].
put youth with ADHD at high risk of problems associated with Influenced by major theories on neuronal circuits, genetic
aggressivenessinadulthood[Klassenetal.,2010],especiallywhen associationstudiesofADHDand/oraggressionhavebeendomi-
theaggressivebehaviorhasanearlyonset[Hofvanderetal.,2009]. nated by candidate gene studies, focusing on the regulation of
BREVIK ET AL. 735
monoaminergictransmission[Faraoneetal.,2015;Veroudeetal., biologicalpathwaysinvolvedinADHDand/oraggressiveness,as
2015].Inlinewithtwinstudies,thesecandidategeneanalyseshave the majority of GWA findings tend to reside outside the tradi-
provided further support toward a shared genetic component tional protein-coding regions [Dick et al., 2011; Schizophrenia
between ADHD and aggression. Many genes associated with Working Group of the Psychiatric Genomics, 2014].
ADHD point toward the same biological mechanisms as those Inthepresentstudy,weaimedtoperformexploratorygenome-
associated with aggressive behavior, including genes that are wideassociationteststoshedlightonthegeneticsusceptibilityloci
involved in the synthesis, binding, transport and degradation of and biological processes possibly involved in the etiology of
neurotransmitters, especially dopamine and serotonin [Faraone childhoodaggressivenessinADHD.WeutilizedtheGWAmethod
etal.,2015;Veroudeetal.,2015].Ithasbeenreported,forexample, toanalyzechildhoodaggressivenessinadultswithADHDgathered
thatthegenesMAOA,DRD2,DRD4,COMT,SLC6A4,TPH1,and in studies across Europe. To minimize phenotypic heterogeneity
TPH2 may contribute to the development of ADHD as well as between samples, we derived our measure of childhood aggres-
aggressive behaviors [Gizer et al., 2009; Vassos et al., 2014]. sivenessinadultADHD(aADHD)fromtheWenderUtahRating
However, these candidate gene studies suffer from the lack of Scale(WURS).Thisquestionnairewasusedaspartoftheassess-
replication in independent samples (where available) and small ment procedure at all sites. As the WURS reflects childhood
effectsizessuggestthatsomeofthesegenesplayamorelimitedrole recollections,wealsoexploredapossiblegeneticoverlapofassoci-
inthesusceptibilitytoADHDand/oraggressivebehavior,orthat ation signals observed in aADHD with those of irritable and
theirinvolvementmaybelimitedtorarefamilialcases[McKinney defiant/vindictive dimensions of ODD in youth with ADHD
etal.,2008;Halmoyetal.,2010;Tiihonenetal.,2014].Thus,the (cADHD) [Aebietal.,2015].Finally,weperformedanexamina-
overall genetic architecture of ADHD and/or aggression remains tion of non-protein coding genes in order to obtain a better
largely unknown and warrants studies using a hypothesis-free understanding of the biological processes underlying childhood
approach [Vassos et al.,2014]. aggressiveness in aADHD.
Genome-wide association (GWA) studies allow interrogation
of the entire genome to generate new hypotheses. To date, few MATERIALS AND METHODS
GWA studies have been performed for ADHD and/or aggres-
Subjects
siveness, with no finding passing the stringent Bonferroni-
corrected genome-wide significance level (P<5.00E-08) for aADHD samples. Recruitment of adult ADHD patients
either phenotype [Dick et al., 2011; Tielbeek et al., 2012; Mick was conducted at three sites within an international multi-
et al., 2014; Salvatore et al., 2015]. Nonetheless, as these studies center persistent ADHD collaboration (IMpACT, http://www.
were generally underpowered, some understanding of biological impactadhdgenomics.com): Germany, Norway, and Spain. All
processesbehindADHDand/oraggressivenessmayemergefrom individuals were of Caucasian ancestry. Only participants who
theconvergenceofidentifiednominallysignificantloci.Previous gavewritteninformedconsentwereenrolledinthestudies,which
GWA studies on aggressive behaviors in ADHD have noted a complied with theDeclaration of Helsinki.
number of suggestive association signals, generating biological German sample. Patients with a diagnosis of aADHD were
hypotheses regarding the etiology of ADHD and/or aggression recruited by experienced psychiatrists at the University of
[Anneyetal.,2008;Aebietal.,2015].Inaddition,arecentGWA Wu€rzburg (Wu€rzburg, Germany). Unrelated in- and outpatients
study revealed a positive linear correlation between ADHD of self-reported central-European descent completed a semi-
polygenic scores and comorbid aggression scores, indicating structured clinical interview according to DSM-IV. Inclusion
that the presence of aggressive symptoms in ADHD is likely to criteria were onset before the age of 7 years, lifelong persistence,
index a greater genetic load [Hamshere et al., 2013]. Similarly currentdiagnosisandageofrecruitmentbetween18and65years.
hypothesis-free,genome-widelinkageanalyseshavealsoreported Exclusioncriteria weretheappearanceofsymptomsrestricted to
evidence of significant co-segregation between ADHD and dis- thedurationofanyotherAxisIdisorder;currentdiagnosisofactive
ruptive behavior [Jain et al., 2007]. alcohol or other drug abuse or dependence; lifetime diagnosis of
Thelackofrobustgeneticassociationsignalsmaybeexplained bipolarIdisorder,schizophrenia,oranyotherpsychoticdisorder;
by the modest sample sizes and the complex nature of both andanIQscorebelow80.Foramoredetailedsampledescription,
ADHDandaggressiveness,wheregeneticfactorsareintertwined pleaseconferpreviouspublications[Reifetal.,2009;Frankeetal.,
with environmental influences [Brendgen et al., 2006]. In addi- 2010]. The study was approved by the Ethic Committee of the
tion,heterogeneityingeneticsusceptibility,phenotypicmanifes- University of Wu€rzburg (Wu€rzburg, Germany).
tation, and operationalization of aggressiveness may depress Norwegiansample. ParticipantswererecruitedattheUniver-
association signals [Cross-Disorder Group of the Psychiatric sity of Bergen (UiB, Bergen, Norway) as described elsewhere
Genomics et al., 2013]. The phenotypic heterogeneity in [Halmoy et al., 2009]. In short, adult patients with ADHD were
ADHD may potentially be exacerbated by its high rates of recruitedthroughaNorwegiannationalmedicalregistryaswellas
comorbidity with not only aggressive behaviors, but also bypsychologistsandpsychiatristsworkingatoutpatientclinics.All
mood and anxiety disorders [Biederman et al., 1992]. Another patients had been previously diagnosed with ADHD using either
possible reason behind the lack of replicable genetic findings is DSM-IVorICD-10.TheICD-10criteriawereadaptedtotheDSM-
the limited annotation of the human genome. The annotation IVcriteriabyallowingtheinattentivesubtypeassufficientforthe
has mostly been focused on protein-coding genes that represent ADHD diagnosis. Individuals with other neuropsychiatric disor-
only(cid:4)1%ofourgenome,makingitdifficulttoevaluatepossible derswerenotexcludedaslongastheADHDcriteriawerefulfilled.
736 AMERICAN JOURNAL OF MEDICAL GENETICS PART B
Individuals with IQ below 70 were excluded from the study. All was adopted as a continuous measure of aggressiveness, ranging
participants provided either blood or saliva samples for DNA from0to24.SupplementaryFigureS1showsthedistributionof
extraction. The study was approved by the regional committee this measureacrossgenders inthe three aADHDdatasets.
formedical and health researchethics, western Norway. cADHD sample. The dimensions of oppositionality were
Spanish sample. Participants were recruited at the Depart- assessedusingthelongformoftherevisedConnersParentRating
mentofPsychiatryfromtheHospitalUniversitariValld’Hebron Scale (CPRS-R:L) [Conners et al., 1998]. The defiant/vindictive
(HUVH,Barcelona,Spain)asdescribedelsewhere[Sanchez-Mora and irritable dimensions of ODD were defined on theoretical
et al., 2015]. Patients were adults of Caucasian origin and met grounds as described elsewhere [Aebi et al., 2015], and reflect
DiagnosticandStatisticalManualforMentalDisorders-IV(DSM- two previously described dimensions of ODD [Stringaris et al.,
IV)criteriaforADHD.ThediagnosisofADHDwasevaluatedwith 2012; Aebi et al., 2013].
the Structured Clinical Interview for DSM-IV Axis I and II Dis-
orders (SCID-I and SCID-II) and the Conner’s Adult ADHD Genotype Data
Diagnostic Interview for DSM-IV (CAADID Parts I and II).
Consensuseligibilitycriteriaforthecurrentstudywereadiagnosis Genotyping of each sample was performed by each of the four
of ADHD according to the diagnostic criteria of DSM-IV, onset participating groups,individually. To maximize available genetic
before the age of 7 years via retrospective diagnosis (which was information among examined datasets, genetic imputation was
confirmed by a family member, wherever possible), lifelong per- carried out independently ateach site.
sistence and current diagnosis. DNA was extracted from either
peripheralbloodorsalivasamples.Thestudywasapprovedbythe
aADHD Samples
ethics committee ofthe institution.
cADHD sample. Youth with ADHD were participants in the German sample. Genotyping of participants was performed
International Multicentre ADHD Genetics (IMAGE) study, on Illumina’s PsychChip array (Illumina, San Diego, CA) at the
recruited in 12 children and adolescent psychiatry clinics repre- BroadInstitute(Cambridge,MA)usingthePsychChip15048346B
senting eight countries across Europe. Approvalwas obtained by manifest. Genotypes were assigned in Illumina’s GenomeStudio
theInstitutionalReviewBoardofSUNYUpstateMedicalUniver- v2010.3, using the calling algorithm/genotyping module version
sityandfromethicalreviewboardswithineachcountry.Adetailed 1.8.4. Quality control procedures were performed as described
descriptionofthestudydesignandassessmentprocedureshasbeen previously,withlightlymodifiedexclusioncriteria(SNPsexhibit-
providedinpreviouspublications[Mulleretal.,2011a,b].Inshort, ing missingness above 98%; minor allele frequency below 5%;
entry criteria for probands were a clinical diagnosis of ADHD failingHardy–Weinbergequilibriumtest[P<10(cid:3)4])[Zayatsetal.,
according to DSM-IV-based structured interviews and access to 2015]. Genotype imputation was performed with SHAPEIT/
one or both biological parents and one or more full siblings for IMPUTE2 pipeline as described elsewhere, using 1000 Genomes
DNAcollectionandclinicalassessment.Exclusioncriteriaincluded Phase3dataasareference[Marchinietal.,2007;Howieetal.,2009;
autism, epilepsy, IQ<70, brain disorders, and any genetic or Cross-Disorder Group ofthe Psychiatric Genomics,2013].
medical disorder associated with externalizing behaviors that Norwegian sample. Participants were genotyped on Human
might mimicADHD. OmniExpress-12v1-1_B(Illumina,SanDiego,CA)platformatthe
deCODE Genetics facility (Reykjavik, Iceland). Genotyping and
quality control procedures are described elsewhere [Zayats et al.,
Measures of Aggressiveness
2015]. Imputation was performed utilizing IMPUTE software as
aADHD samples. The adult measure of childhood aggres- previouslydetailed[Marchinietal.,2007;Howieetal.,2009;Cross-
siveness in the aADHD samples was derived from the Wender Disorder Group of the PsychiatricGenomics, 2013].
Utah Rating Scale (WURS) [Ward et al., 1993]. The WURS is a Spanish sample. Genome-wide genotyping was performed
questionnaire used for retrospective assessment of childhood withtheIlluminaHumanOmni1-QuadBeadChipplatform.Qual-
symptoms of ADHD in adults. An exploratory factor analysis itycontrolwasimplementedattheindividualandSNPlevelusing
(EFA) was run to determine the latent structure of the WURS. PLINKandincludedfilteringsubjectswithlowcallrate(<98%)or
TheEFAconsistedofaprincipalcomponentanalysiswithVarimax gender discrepancy followed by filtering SNPs with minor allele
rotation and yielded three factors with Eigen values above one. frequency (MAF)<0.01, Hardy–Weinberg equilibrium test
Fromthemainfactorexplainingthegreatestamountofvariancein P-values<1e-06 or call rate<0.99 in either cases or controls.
responsestotheWURS(30.7%),thetopsixitemswiththehighest Imputation was performed using BEAGLE software [Browning
loadings (0.74–0.82) all represented prototypical elements of andBrowning, 2007].
aggressiveness: “temper outburst/tantrums,” “angry,” “hot- or cADHD sample. Sample collection and DNA isolation has
short-tempered/low boiling point,” “disobedient with parents/ been described previously [Brookes et al., 2006]. Genome-wide
rebellious/sassy,” “losing control of myself,” and “irritable,” For genotypingandqualitycontrolwasperformedaspartoftheGAIN
eachitem,theparticipantwasaskedtoevaluateifshe/heasachild studyusingthePerlegen600Kgenotypingplatform,aspreviously
was (or had) a specific symptom and to rate it according to the described[Nealeetal.,2008].Theimputationwasperformedusing
following four response categories: “not at all/very slightly” (0), MACHandtheHapmap2(Release22Build36)referencedataset
“mildly”(1),“moderately”(2),quiteabit”(3),or“verymuch”(4). [Li et al., 2010]. Quality control was performed on the imputed
Thearithmeticsumoftheresponsesoftheaforementioneditems data,andSNPswithimputationqualityscoreslowerthan0.30,a
BREVIK ET AL. 737
minor allele frequency lower than 0.01, and those failing the Genome-wide enrichment analyses between GWA results in
Hardy–Weinberg equilibrium test at a threshold of P(cid:5)10(cid:3)5 aADHDandcADHDsamples. Priortoperformingenrichment
were excluded. SNPs and subjects with missingness rates higher analyses, the genetic data in both aADHD and cADHD samples
than 0.05 wereremoved from the data. were pruned to remove correlated loci in linkage disequilibrium
(LD) with each other. A pairwise correlation coefficient (r2)
threshold of 0.2 and the 1000 Genomes CEU reference dataset
Statistical Analyses
were used to identify independent SNPs, as previously described
TheageandgenderdistributionsbetweentheaADHDandcADHD [Lindgrenet al., 2009; Genomes Project et al., 2012].
samples were assessed using x2for gender andANOVAfor age. EnrichmentwasexaminedbymeansofFisher’stestperformed
Genome-wide association (GWA) of aggressiveness. In the in the R software, assessing the difference in proportion of
aADHD sample, single nucleotide polymorphisms (SNPs) were SNPs revealing association P-values below 0.05 in the cADHD
tested forassociation with the WURS-derived measure of aggres- sampleaccordingtosuggestiveassociationintheaADHDsample
sivenessintheformoflinearregressioncarriedoutinPLINKusing (P-valuebeloworequalto1.00E-03versusP-valueabove1.00E-03)
post-imputation dosage data [Purcell et al., 2007]. Regression [Rahmioglu et al., 2015]. Consistency in directionality of SNP
models were adjusted for age and sex. Genotype data of each site effects with indication of enrichment between aADHD and
werefirstprocessedindividually.Theresultswerethencombined cADHD samples was tested as linear regression on the effect
with the use of fixed-effects inverse variance meta-analysis in (beta) of each SNP for aADHD as an outcome and for cADHD
METAL[Willeretal.,2010].OnlySNPswithminorallelefrequency (eitherirritableordefiant/vindictivedimensionsofODD,respec-
(MAF)equaltoorabove1%andimputationINFOmeasureequalto tively) as predictor variables [Doet al., 2013].
orabove0.6wereincludedintheanalyses.Genomiccontrol,QQ Examination of previously reported aggressiveness-related
plotting,andregionalplottingoftoplociwereappliedtocheckthe candidateGWAloci. Weassembledalistofpreviouslyreported
integrityofteststatistics[DevlinandRoeder,1999;Cuellar-Partida candidate GWA loci associated with aggressive behavior by
et al., 2015]. The genomic inflation factor was calculated using systematic literature search the catalog of published genome-
METAL[Willeretal.,2010].Agenome-widesignificancethreshold wide association studies provided by National Human Genome
of5.00E-08wasadoptedtocorrectformultipletesting. ResearchInstitute(NHGRI)(https://www.genome.gov/26525384),
GWAanalysesofirritableanddefiant/vindictivedimensionsof using key words of “aggression,” “anger,” “violence,” as well as
ODDincADHDsamplewasperformedinPLINKsoftwareinthe “conduct disorder” and “antisocial personality disorder.” Each
form of linear regression adjusted for sex and age [Purcell identified candidate GWA locus was then looked up in meta-
et al., 2007]. Details of the analyses are described elsewhere analyzedaADHDsample.
[Aebi et al., 2015].
Gene-based and Gene-set association of aggressiveness in the
RESULTS
aADHDmeta-analyzedsample. Gene-basedandgene-setpath-
wayanalysiswereperformedintheaADHDsamplecarriedoutin Subjects, Measure of Aggressiveness, and
MAGMA software [de Leeuw et al., 2015]. First, a degree of
GWA Analyses
associationwascalculatedforeachgenebasedonMETAL-derived
individualSNPs’P-values,using1000GenomesCEUdatasetasa Intotal,1,060adultpatientsaswellas750childrenandadolescentswith
reference panel to correct for linkage disequilibrium (LD) ADHDwereavailablefortheanalyses.TheagerangesintheaADHD
[GenomesProjectetal.,2012].Toevaluateeachgene’scontribu- sampleswere17–75intheGermansample,18–57intheNorwegian
tiontoexaminedgene-sets(gene-setpathwayanalysis),theP-value sample,and17–60intheSpanishsample.InthecADHDsample,the
ofeachgenewasconvertedtoaZ-valueandusedasanoutcome age range was 5–17. Details of the final samples are summarized in
variable in a regression model with gene-set membership as a Table I. Supplementary Figure S1 presents the distribution of the
predictor. Gene size and gene-sets’ gene density were added as selectedmeasureofaggressivenessineachaADHDdataset.
covariates to adjust for possible confounding effects and prevent After quality control of imputed SNPs in the adult samples,
spurious association. 9.301.568 SNPs were available for the analyses in the German
For gene-based tests, we assessed the association with both sample, 8.910.491 SNPs in the Norwegian sample, and 6.683.176
protein and non-protein-coding genes. The protein-coding gene SNPsintheSpanishsample.Amongthesethreedatasets,7.576.458
listwascuratedfromthecatalogofknowngenesdownloadedfrom autosomalSNPswerepresentinatleasttwoand,thus,weremeta-
the Genome Browser of the University of California Santa Cruz analyzedtoassessgeneticarchitectureofchildhoodaggressiveness
(UCSC,CA).Thenon-protein-codinggeneswereexaminedinthe in aADHD. In cADHD sample, 1.871.025 autosomal SNPs were
form of long non-coding RNA (lncRNA) genes detailed in the available for the analyses.
aforementionedcatalog.Forgene-setpathwayanalysis,weexam- IndividualGWAanalysesrevealednogenome-widesignificanthits
ined structural categories of gene ontology (GO, http:// (P(cid:5)5.00E-08) in either aADHD sample (not shown) nor in the
geneontology.org), with respect to cellular function, biological cADHDsample(SupplementaryTableSIandFig.S2).Noneofthe
processandcellularcompartments.Toachievemeaningfulstatis- variants in the meta-analysis reached the Bonferroni-corrected
tics and interpretation of the results, we restricted our pathway genome-widesignificancelevel(P(cid:5)5.00E-08)either.Thestrongest
analysistothoseGOtermsthatcontainedSNPsinatleast10genes signalwasobservedatrs10826548onchromosome10locatedwithin
perterm inour aADHDdata. the transcript of a long noncoding RNA (lncRNA) (beta¼(cid:3)1.66,
738 AMERICAN JOURNAL OF MEDICAL GENETICS PART B
TABLE I. Details of the ADHD Patient Samples
aADHD samples
IMpACTsite Numberof participants Females(%) Age(mean(cid:6)SD) Aggressiveness score (mean(cid:6)SD)
Germany 368 53.0 35.18(cid:6)10.53 11.33(cid:6)5.17
Norway 293 52.6 32.61(cid:6)11.00 12.10(cid:6)6.39
Spain 399 32.3 31.31(cid:6)12.39 10.19(cid:6)6.15
Total 1,060 45.1 33.01(cid:6)11.51 11.11(cid:6)5.94
cADHD sample
ODDscores (mean(cid:6)SD)
Numberofparticipants Femalesa (%) Ageb(mean(cid:6)SD) Irritable Defiant/vindictive
IMAGE 750 12.3 10.67(cid:6)2.77 7.75(cid:6)3.06 8.95(cid:6)4.18
SD,standarddeviation.
AggressivenessscorewasderivedfromWURSintheaADHDsample.InthecADHDsample,dimensionsofoppositionality(irritableanddefiant/vindictivedimensions)wereexamined[Aebietal.,2015].
aDifferenceintheproportionoffemalesbetweentheaADHDandcADHDsamples:P<2.2E-16(x2test).
bDifferenceinagebetweentheaADHDandcADHDsamples:P<2.2E-16(ANOVA).
standard error (SE)¼0.34, P-value¼1.07E-06) (Fig. 1), closely cADHD, we investigated the independent (r2<0.2) GWA sig-
followedbyrs35974940intheneurotrimin(NTM)gene(beta¼3.23, nals of suggestive significance (P(cid:5)1.00E-03) in aADHD for
SE¼0.67, P-value¼1.26E-06) (Fig. 2). Top associated markers enrichment in GWA signals of either defiant/vindictive or
(P(cid:5)1.00E-05) are summarized in Supplementary Table SII. The irritable dimensions in cADHD. Given our modest sample
genomicinflationfactorwasclosetooneforallindividualandmeta- size, only those SNPs were considered in cADHD results that
GWAanalysesinaADHD.QQplotsofGWAanalysesinaADHDare revealedaP-valuebeloworequalto0.05toavoidtheexamina-
presentedinSupplementaryFigureS3. tion of effects with a wide confidence interval. The top GWA
SNPs of WURS-derived childhood aggressiveness in aADHD
Gene-Based and Gene-Set Association showed significant enrichment of signals from both the
of Aggressiveness in the aADHD defiant/vindictive dimension (Fisher’s P-value¼2.28E-06) and
the irritable dimension in cADHD GWA analysis (Fisher’s
Meta-Analyzed Sample
P-value¼0.0061; Fig. 3A).
Amongannotatedprotein-codinggenes,17.595hadmorethanone Next,weexaminedthedirectionalityofeffectsofvariantswith
SNPpresentintheaADHDdata.Thestrongestsignalwasnotedfor associationsignalsinbothaADHDandcADHDsamples(P(cid:5)1.00
the WD repeat domain 62 (WDR62) gene (P-value¼4.84E-05). E-03inaADHDandP<0.05incADHD).Significantcorrelation
SupplementaryTableSIIIsummarizesthetopprotein-codinggenes between betas was observed in assessment of both oppositional
(P(cid:5)1.00E-03)observedinaADHDsample.Noneoftheprotein- dimensions in cADHD and childhood aggressiveness in aADHD
codinggene-basedtestssurvivedthecorrectionformultipletesting. (P¼0.0053and0.0045fordefiant/vindictiveandirritabledimen-
AmonglncRNAgenes,22.696hadmorethanoneSNPpresentin sionsrespectively),butthedirectionoftherelationshipwasnega-
our aADHD data. The strongest association was observed for tive(Fig.3BandC).SupplementaryTableSVIIsummarizesthetop
ENST00000427806 (P-value¼3.04E-05). The top lncRNA genes hits(P(cid:5)1-00E-05)observedinGWAmeta-analysisofchildhood
(P(cid:5)1.00E-03)detectedinthisstudyarereportedinSupplemen- aggressiveness in aADHD and their corresponding statistics
taryTableSIV.Noneofthenon-protein-codinggene-basedtests observed in cADHD.
survived the correctionfor multiple testing.
AmongGOpathways,1.945termscontainedSNPsinatleast10
Examination of Previously Reported
genespertermintheaADHDdata.Themostprominentassociation
wasobservedfornegativeregulationofI-kappaBkinase/NF-kappaB Aggressiveness-Related Candidate Genes
signaling pathway (GO:0043124 term, P-value¼7.26E-04). Sup- and GWA Loci
plementaryTableSVreportstopGOterms(P(cid:5)0.01)recognizedin
this study. None of the GO pathways survived the correction for Among previously reported aggressiveness-related GWA loci,
multipletesting. severalSNPsnotedtobeassociatedwithanger,conductdisorder
and adult anti-social personality disorder revealed P-values
Genome-Wide Enrichment Analyses Between below 0.05 in our study (Supplementary Table SVIII). The
strongestsignalintheGWAanalysisofchildhoodaggressiveness
GWA Results in aADHD and cADHD Samples
in aADHD among the aforementioned loci was observed for
To assess potential genome-wide overlap of association signals rs4889240 in the PKD1L2 (polycystic kidney disease 1-like 2)
between measures of childhood aggressiveness in aADHD and gene (beta¼(cid:3)0.73, SE¼0.25, P-value¼0.0039), previously
BREVIK ET AL. 739
FIG.1. Plotofthelocussurroundingrs10826548.SNPsareplottedbypositiononchromosome10againstGWAP-valuesforaggressive
behaviormeasureinaADHD.EstimatedrecombinationratesfromHapMapareplottedinbrightredtoreflectlocalLDstructure.TheSNPs
surroundingrs10826548arecolor-codedtoreflecttheirLDwithit(accordingtopair-wiser2valuesfromtheHapMapCEUdatabase).SNPs
withLDr2(cid:7)0.2areplottedatthebottomofthegraphwithLDcolor-codingspecifiedinthetoprightcorner.“Genes”referstoprotein-coding
genesinthepresentedregion.“lincRNAsAllCellTypeTopView”reflectsthedatafromlncRNAUSCStrackinbraintissue.“tfbsConsSites”reflects
theTFBSUCSCtrack.
DISCUSSION
reported to be associated with CD symptom count in ADHD
patients. The same SNP also revealed nominally significant
association in the same direction with the defiant/vindictive Inthisstudy,weperformedagenome-wideexplorationofchild-
dimension (beta¼(cid:3)0.54, SE¼0.21, P-value¼0.0094), but not hood aggressiveness as reported retrospectively by adult patients
withtheirritabledimensionincADHD.Inthisresult,oneshould with ADHD (aADHD), examining both conventional protein-
keep in mind that the cADHD described here is a subsample of coding and lncRNA genes. We also explored the overlap with
the sample in which the original finding for rs4889240 was parent-reported oppositional behavior in youth with ADHD
described[Aebiet al., 2015]. Full resultsofour literature search (cADHD) and evaluated previously reported aggression-related
are presented in Supplementary Table SVIII. GWAloci.Givenourmodestsamplesize(1060aADHDpatients)
740 AMERICAN JOURNAL OF MEDICAL GENETICS PART B
FIG.2. Plotofthelocussurroundingrs35974940.SNPsareplottedbypositiononchromosome11againstGWAP-valuesforaggressive
behaviormeasureinaADHD.EstimatedrecombinationratesfromHapMapareplottedinbrightredtoreflectlocalLDstructure.TheSNPs
surroundingrs35974940arecolor-codedtoreflecttheirLDwithit(accordingtopair-wiser2valuesfromtheHapMapCEUdatabase).SNPs
withLDr2(cid:7)0.2areplottedatthebottomofthegraphwithLDcolor-codingspecifiedinthetoprightcorner.“Genes”referstoprotein-coding
genesinthepresentedregion.“lincRNAsAllCellTypeTopView”reflectsthedatafromlncRNAUSCStrackinbraintissue.“tfbsConsSites”reflects
theTFBSUCSCtrack.
and the anticipated small effect of common polymorphisms in (beta¼(cid:3)1.16, SE¼0.34, P¼1.07E-06, Supplementary
complex traits, it is not surprising that we did not observe any Table SI). This variant resides in the transcript of a lncRNA
genome-wide significant SNPs (P<5.00E-08). Nonetheless, we with uncertain coding potential (TCONS_00018147) (Fig. 1).
were able to identify several nominally significant variants Non-proteincodingRNAsplayacriticalroleintheregulationof
(P(cid:5)1.00E-05) in biologically interesting genes for follow-up gene expression and have been previously associated with neu-
studies of aggressiveness in ADHD, a feature of the disorder ropsychiatric disorders, including ADHD [Perkins et al., 2005;
that hasreceived little attention so far. Gonzalez-Giraldoetal.,2015;Zayatsetal.,2015].Inaddition,it
Thestrongestsignalintheperformedsingle-pointGWAtests has recently been observed that SNPs previously associated
ofchildhoodaggressivenessinaADHDwasnotedforrs10826548 with neurological and psychiatric conditions may be highly
BREVIK ET AL. 741
FIG.3. EnrichmentanddirectionofeffectamongGWAsignalsofoppositionaldimensionsincADHDandWURS-derivedchildhood
aggressivenessinaADHD.PartAreflectstheproportionofSNPsnominallyassociated(P<0.05)witheachexaminedoppositionaldimension
incADHD(defiant/vindictiveandirritable)amongsuggestivesignals(P(cid:5)1.00E-03)ofassociationwithchildhoodaggressivenessinaADHD.
ReportedP-valuesarethoseofFisher’sexacttest.PartsBandCreflectdirectionsofeffectof24independentnominallysignificantlociin
GWAanalysesofdefiant/vindictivedimensionincADHDandchildhoodaggressivenessinaADHD(partB)aswellas17independentnominally
significantlociinGWAanalysesofirritabledimensionincADHDandchildhoodaggressivenessinaADHD(partC).Linearregressionr2
measuresandP-valuesareshown.
concentrated in the regions of long non-protein coding RNA P-values of 3.59E-06 and 3.25E-06, respectively, Supplementary
genes [Ning et al., 2014]. Table SI) are transcription factor binding sites (TFBS) (Fig. 2).
The second most significant locus identified in this study is Moreover,twootherSNPsinhighlinkagedisequilibriumwiththe
locatedwithintheneurotrimin(NTM)gene(intronicrs35974940, aforementioned ones (rs12804059 and rs7119590, r2¼1 in CEU
P¼1.26E-06, Supplementary Table SI and Fig. S2). NTM is a population)alsorepresentTFBS.Notably,differentialexpression
protein-codinggene,encodingamemberofglycosylphosphatidy- of NTM between two major brain regions linked to aggression
linositol (GPI)-anchored cell adhesion molecules, containing subtypes—prefrontal cortex and amygdala—was observed in
immunoglobulin(Ig)domain.Theseproteinsarepredominantly early prenatal stage of human brain development (P¼0.015,
expressedinthecentralnervoussystem(CNS)[Struyketal.,1995]. http://www.brainspan.org).
Among the association signals observed in NTM gene, several Geneexpressionregulationduringneuronaldevelopmentasoneof
have the potential to alter its expression. As determined in thepossiblemechanismsbehindaggressivenessinaADHDwasfurther
the TRANSFAC database implemented in the SNPinfo server affirmed by our top associated lncRNA gene—ENST00000427806
of the National Institute of Environmental Health Sciences (P¼3.04E-05, Supplementary Table SIV). The target gene of
(http://snpinfo.niehs.nih.gov),rs34588147andrs35665773(GWA this lncRNA has been predicted to be the protein-coding ST6
742 AMERICAN JOURNAL OF MEDICAL GENETICS PART B
(alpha-N-acetyl-neuraminyl-2,3-beta-galactosyl-1,3)-N-acetylgalac- This study should be viewed in light of its limitations. One
tosaminide alpha-2,6-sialyltransferase 5 (ST6GALNAC5) gene explanation for not observing any genome-wide significant loci
[Vucicevicetal.,2015].TheproteinencodedbyST6GALNAC5isa (P<5.00E-08) could be our relatively modest sample size and
memberofsialyltransferases,withreportedfunctionincelladhesion examination of common variants only (MAF>1%). This study
throughcell–cellandcell–extracellularmatrixinteractions[Tsuchida had63%powertodetectcommonvariantswithsmalleffectsizeof
et al., 2003]. Intriguingly, ST6GALNAC5, similarly to NTM, also explaining 0.5% of variability under an additive model and
revealed differential expression in the aggression-related structures an alpha level of 0.05 (http://genome.sph.umich.edu/wiki/
ofprefrontalcortexandamygdalainearlyprenatalstagesofhuman Power_Calculations: Quantitative_Traits). This may also be
braindevelopment(P¼0.013;http://www.brainspan.org). observed in the distribution of the QQ plots (Supplementary
As the adult measure of aggressiveness was derived from self- Fig. S3).
reportedexperiencesinchildhood,weexaminedthepossibilityof Anotherexplanationforthelackofsignificantfindingsmaylay
overlapofitsGWAsignalswiththosefromGWAanalysesoftwo inphenotypicvariability.Clinicalheterogeneitymayweakentrue
oppositionaldimensionsinacADHDsample.Weobservedaslight associationsignalsduetotheuseofdifferentassessmentprotocols
enrichmentofassociationsignalsbetweenthenominallyassociated orrealgeneticheterogeneityamongsubtypesofADHD[McClellan
lociinaADHDandthoseobservedintheGWAofboththedefiant/ and King, 2010]. There are several methodological caveats to
vindictiveandtheirritableODDdimensionsexaminedincADHD assessing aggressiveness [Moffitt et al., 2015]. As our samples
(Fig.3).However,itisnoteworthythattheaADHDandcADHD consist of outpatients, we investigate a broader and perhaps
sampleswereimputedusingdifferentreferencepanelswithdispa- “softer” aspect of aggressiveness than say, for example, if we
rate genomiccoverage. weretostudyprisoninmatesand/orjuvenileoffenders.However,
Surprisingly,thecorrelationbetweenthedirectionofeffectsofthe this approach provides us with access to the vast majority of
aforementionedSNPswasnegative(Fig.3BandC).Suchaninverse aggressivebehaviors,whichmaynotcometobewritteninofficial
relationshipineffectdirectionalitybetweenparent-reportedODD records [Moffitt, 2005]. Furthermore, we lack assessment of dif-
dimensions and adult retrospective report of childhood aggres- ferent subtypes of aggressive behavior that may be related to
siveness is most likely a chance finding due to our study being different genotypes.
under-powered.Itmightalsoberelatedtophenotypicandgenetic Considering the different direction of effects and different
heterogeneity of the examined samples. There were considerable measures of aggression in the cADHD and the aADHD samples,
differencesinthepercentageoffemalesbetweentheaADHDandthe analyzingtheadultsamplesandtheyouthsampletogethercould
cADHDsamples(TableI),whichcouldindicatesuchmechanisms. potentiallyhaveobscuredthegeneticassociationsignal.Thisiswhy
It has been shown that both age and sex are importantfactors in we refrained from performing meta-analysis across all samples.
geneticinfluencesinADHDandaggression[Lyonsetal.,1995;Miles Nonetheless, the WURS includes a host of symptoms related to
andCarey,1997;TuvbladandBaker,2011;Faraoneetal.,2015].In various elements of aggressiveness, which, based on our factor
addition,theaggressivenessinthecADHDsamplewasdetermined analysisaswellaspreviousresearch[Wardetal.,1993]seemtobe
byparent-report,whereasintheaADHDsample,itwasbasedon of key importance to the phenotype of aADHD, and the ODD
retrospectiveself-report.Thecorrelationbetweenparent-reportand measureshavealsobeenvalidatedinpreviousstudiesofcADHD
self-reporthasbeenshowntobegenerallypoor[Achenbachetal., [Stringarisetal.,2012;Aebietal.,2013].Ourapproachmayaddto
1987],asalsodiscussedinarecentstudythatfoundlittleoverlap the discussion of the Negative Valence System in the Research
between samples of cADHD and aADHD [Moffitt et al., 2015]. Domain Criteria (RDoC) of the National Institute of Mental
Hence, the measures of aggressiveness in the cADHD and the Health (NIMH) of how to conceptualize and operationalize
aADHD samples are different. Furthermore, the youth and adult aggressiveness as a dimension across different samples and dis-
ADHD samples may also be heterogeneous because childhood orders [Verona andBresin, 2015; Veroude et al., 2015].
ADHD does not always persist into adulthood [Faraone et al., We lacked information on current substance abuse in our
2006; Moffitt et al., 2015]. Thus, to gain better understanding of aADHD sample. Substance abuse is known to be frequently
thegeneticoverlapbetweenchildhoodaggressioninaADHDand comorbidwithADHDandmayconfoundtherelationshipbetween
oppositional dimensions in cADHD, this relationship should be ADHD andcurrentaggressiveness.However, we utilized aretro-
examinedinlargersampleusingmorerigorousstatisticalmethods, spectivemeasureofchildhoodaggressivenessthatislikelytoreflect
such as those developed to test specifically forgenetic correlation behavior over a longer period of time and should, thus, be less
among various traits [Yang et al., 2011; Bulik-Sullivan et al., affected by volatile environmental influences [Gulberg-Kj€ar and
2015a,b].Thiswasnotpossibletoimplementinthecurrentstudy Johansson, 2009].
duetoourmodestsamplesize. Finally, since the genome-wide genotyping arrays consist of
Examinationofpreviouslyreportedaggressiveness-relatedGWA SNPsonly,wewerenotabletoassessthecontributionofpreviously
locirevealedmodestcommonalityingeneticarchitecturebetweenthe reportedvariabletandemrepeats(e.g.,thoseinMAOA)thatwere
childhoodmeasuresofaggressivenessinbothcADHDandaADHD, noted to be associatedwith aggressive behaviors and/or ADHD.
aswellasinCDandanti-socialpersonalitydisorder(Supplementary Takentogetherwithevidencefrompreviousstudies,ourresults
TableSVIII).Thisobservationmaybeinlinewithformerlyreported implicatemechanismsofcelladhesionaswellasregulationofgene
phenotypic overlap between these conditions, although to which expressionintheetiologyofchildhoodaggressivenessinADHD.
extentthisoverlapcanbetransmittedtovarioussubtypesofaggres- Asthereisasubstantialdegreeofoverlapinaggressivenessamong
sivenessremainstobedetermined[StoreboandSimonsen,2013]. neuropsychiatric disorders, it could be beneficial to analyze