Nature and nurture in behavioral problems Eco de Geus Department of Biological Psychology, Neuroscience Campus / EMGO + institute VU University, Amsterdam The Netherlands
Topics Quantitative Genetics Genetic variance Genetic covariance between family members Twin Family Studies (aggression & borderline personality) Heritability estimates Sex differences - Gene-environment correlation and interaction Gene Finding studies (conduct disorder & depression) Candidate gene approach Whole genome association
GENES (past) ENVIRONMENT Nature & Nurture GENE x ENVIRONMENT INTERACTION DISPOSITION (current) ENVIRONMENT GENE x ENVIRONMENT CORRELATION BEHAVIOR Pi = µ + Gi + Ei + Gi*Ei Variance(Pi) = variance(g)+variance(e)+variance(g*e)+2*covariance(g,e)
Genetic variance Allele of Father Mother B E2 (CA) 3 b E4 (CA) 9 Ok Toxic Gene = unit of heredity (makes a protein) Locus = physical (base pair) location in a gene Allele = different variants of the gene at a locus (SNP, haplotypes, repeats) Homozygous genotype = paternal and maternal alleles are identical Heterozygous genotype = paternal and maternal alleles are different
Allele of Father Mother Mendelian traits (yes/no) B b Exon T allele for dysfunctional or toxic protein Ok T gm gf gm gf x 1 2 3 T gm gm gm gf gf gm gf gf 1 3 1 T 2 3 2 T 1/4 1/4 1/4 1/4
Allele of Father Mother Quantitative traits B b Regulatory zone b..b increasing alleles for better transcription: more growth protein synthesis Ok Tox d = -4 167 175 (179) 191 bb Bb m BB -a = -12 a = +12 Example: A stature gene with a bi-allelic polymorphism in the regulatory zone of a growth protein yields three types of persons with three different heights: 167, 175, 191 cm.
A breeding (thought!) experiment P homozygote seletion (BB fathers * bb mothers) => F1, all Bb F1 intercross (Bb fathers * Bb mothers) => F2, BB, Bb, bb Genotype (i) BB Bb bb Frequency (f) ¼ ½ ¼ Genotypic effect (x) a d -a f * x ¼ a ½ d -¼ a Mean genetic effect (µ g ) = f i *x i {a=12, d=-4} Genetic variance (V *(x -µ 2 G ) = f i i µ g ) = 12*¼ + -4*½ + -12*¼ = -2 =¼*(12 --2) 2 + ½*(-4 --2) 2 + ¼*(-12 --2) 2 = 76
Non-inbred population in HWE Frequency of B-allele is p; frequency of b-allele is q Hardy Weinberg Equilibrium (HWE): the genotype frequencies are stable across generations Genotype (i) BB Bb bb Frequency (f) p 2 2pq q 2 Genotypic effect (x) a d -a f * x p 2 a 2pqd -q 2 a Mean genetic effect (µ g ) = f i *x i = p 2 a + 2pqd - q 2 a = (1-q) 2 a + 2pqd - q 2 a = a(p-q) + 2pqd Genetic variance (V G ) = f i *(x-µ g ) 2 = p 2 *(2q(a-dp)) 2 +2pq*(a(q-p)+d(1-2pq)) 2 +q 2 *(-2p(a+dq)) 2 = 2pq(a+(q-p)d) p)d) 2 + 4(pqd) 2 V G = V A + V D
Mo co other s a ombinati allele ons Father s allele combinations BC bc Bc bc 2 Genes BC BBCC BbCC BBCc BbCc bc bbcc bbcc bbcc bbcc Bc BBcC BbcC BBcc Bbcc bc bbcc bbcc bbcc bbcc b = decreaser allele (+0), B = increaser allele (+2) c = decreaser allele (+0), C = increaser allele (+2) 9 Genotypes 3n, where n is the number of genes BC bc Bc bc BC μ +8 μ+6 μ +6 μ +4 bc μ +6 μ+4 μ +4 μ +2 Bc μ +6 μ+4 μ +4 μ +2 bc μ +4 μ+2 μ +2 μ +0 5 Phenotypes 2n +1, where n is the number of genes 7 3 Genes 27 Genotypes 7 Phenotypes 6 5 4 Genes 81 Genotypes 9 Phenotypes 4 3 2 1 0 7 6 5 4 3 2 1 0 20 15 10 5 0
Familial resemblance Pi = µ + Ai + Di + Ei +Ci + gene environment interaction terms V P = V A + V D + V E + V C + variance of the gene environment interaction terms + gene-environment covariance terms. COV P (relative1, relative2) = β*v A + γ*v D COV P (sibling, sibling) = ½ V A + ¼ V D + 1V C + δ*v C COV P (parent, offspring) = ½ V A COV P (uncle, nephew) = ¼ V A + 1V C CAVEAT: Family members share part of their environment (SES, Neighborhood, Diet, Parental rearing style, School, etc.). This common environment (C) can also contribute to family resemblance!!!
Monozygotic (MZ,identical) Twin study r MZ =1;r DZ =½ r MZ =1;r DZ =¼ Dizygotic (DZ,fraternal) r MZ =r DZ =1 1 1 1 1 1 1 1 1 E A D C C D A E e a d c c d a e Behavioral trait Twin 1 Behavioral trait Twin 2 Cov Cov (MZ) + (d*1*d) = a 2 + c 2 +d 2 (MZ) = + (d*1*d) = a 2 +d 2 (MZ) = (a*1*a) + (c*1*c) = a 2 +c 2 Cov Cov + (d*¼*d) = ½ a 2 + c 2 + ¼ d 2 (DZ) = (a* ½ *a) + (d*¼*d) = ½ a 2 + ¼ d 2 (DZ) = (a* ½ *a) + (c*1*c) = ½ a 2 + c 2 V V (c*1*c) c +d 2 P = + (d*1*d) + (e*1*e) = a 2 + d 2 + e 2 + P = (a*1*a) + (c*1*c) + (e*1*e) = a 2 + c 2 + e 2 e 2
Sex differences Testable Assumptions: 1. a female = a male ; d female = d male ;e female = de male 2 Same genes influence trait in males and 2. Same genes influence trait in males and females (in DZ twins of opposite sex A factors are.5 correlated; D factors are 0.25 correlated)
Young NTR 2-3 yearly y reports Birth age 2 Maternal smoking, birth weight, Apgar, etc Motor development, growth age 3 age 5 Child Behavior Check List (CBCL) both parents growth, health, parental SES, religion, Devereux Child Behavior mother age 7 CBCL/TRF/Connors both parents & teacher growth, health, parental SES, religion age 10 age 12 CBCL/Connors both parents & TRF teacher growth, etc CBCL/Connors both parents & TRF teacher CITO score, growth, etc Behavior/lifestyle self-report age 12,14,16,18,20,22
Child Behavior Check List items for the Syndrome Aggressive Behavior
Twin correlations Aggressive Behavior 1 08 0.8 0.6 0.4 MZ Male MZ Female DZ Male DZ Female 0.2 DZ OS 0 3 year 5 year 7 year 10 year 12 year Estimates based on mother ratings
Heritability Aggressive Behavior SAME GENES OPERATE IN GIRLS AND BOYS!!
Borderline Personality: PAI-BOR scale (Morey 1991) Mood shifts Little control over anger Feel empty Worry about people leaving AI, Affective instability IP, Identity problems Relationships stormy Let people know they have hurt me Mistakes in picking friends NR, Negative relationships Do things impulsively When upset hurt self Reckless person SH, Self harm
Genetic factor structure BPD A E 0.71 (0.67-0.75) 0.70 (0.66-0.75) BPD 0.58 (0.56-0.60) 0.48 (0.46-0.50) 0.49 (0.47-0.51) 0.28 (0.26-0.30) AI IP NR SH 0.16 0.52 (0.07-0.22) (0.51-0.55) 0.22 0.47 (0.18-0.26) (0.45-0.49) 02 0.23 0.47 036 0.36 066 0.66 (0.19-0.27) (0.45-0.49) (0.32-0.40) (0.63-0.68) A s E s A s E s A s E s A s E s Distel et al., J Personality Disorders, in press
Divorce/ break-up Traffic accident 25 20 25 20 Non-exposed 15 10 15 Non- exposed Exposed 10 Exposed 5 5 0 0 MZ DZ Unrelated MZ DZ Unrelated n=283 n=122 n=301 n=135 n=47 n=147 Violent assault Sexual assault 25 Violent assault 25 25 20 20 20 15 10 15 Not exposed Exposed 10 15 5 0 5 0 MZ DZ Unrelated MZ DZ Unrelated n=87 n=42 n=106 n=76 n=46 n=95 BP 10 25 Robbery 25 Job loss 5 20 15 10 5 20 15 Not exposed Exposed 10 5 0 MZ N=87 DZ N=42 Unrelated N= 109 0 0 MZ DZ Unrelated MZ DZ Unrelated n=281 n=122 n=319 n=196 n=95 n=209 Distel et al., Psychological Medicine, submitted
Modeling gene-environment correlation and gene-environment environment interaction Moderator MZ=1, DZ/sib=0.50 G*E interaction GE correlation Divorce / break-up - + E A A E Traffic accident - - Violent e+ββ e Mod T1 Assault - + e+ββ e Mod T2 a+β a Mod Sexual assault T1 + a+β - a Mod T2 Robbery - - BP m+β m Mod T1 m+β m Mod T2 BP Job-loss - M + Twin1 Twin2 Distel et al., Psychological Medicine, submitted
Gene Hunting Association with candidate genes Testing for a significant association between the trait and a specific variant of a known gene. Linkage analyses Testing for co-segregation of traits and highly polymorphic DNA markers within families. Only the location of the markers is known, the gene may be unknown. Whole genome association Testing for a significant association between the trait and > 100.000000 SNP markers that tag most of the SNP variation in the entire genome.
NTR Biobank Home visit it ~9500 NTR participants pants DNA (blood (& buccal for all twins)) Cell lines RNA (rest & LPS challenge) EDTA, Heparin, Citrate plasma (fresh & frozen) Serum Urine Postal collection of buccal swabs ~7500 NTR participants
Candidate Genes The MAOA enzyme, coded by MAOA gene on the X- chromosome m (Xp11.23) inactivates serotonin (and norepinephrine). A common 30 bp repeat (VNTR) polymorphism in the upstream region (MAOA u-vntr) affects transcription in vitro The presence of 3.5 or 4 repeats is associated with relatively higher her MAOA expression (MAOA-H alleles), whereas the presence of 3 repeats (and, possibly, 5 repeats) results in relatively lower expression (MAOA-L alleles) (Sabol et al., 1998).
Caspi et al, Science, 2002
ONLY IN MALES
Caspi et al, Science, 2003
Genome Wide Association Studies (GWAS) Make no a priori assumptions about the biology of the trait Genotype sufficient SNP/CNV markers on the entire genome to capture the main genetic variation in a population using a discovery sample of 4000 to 40.000000 peoplepl Test association at with the phenotype for ~2.5 million markers r and extract SNP/CNPs surviving multiple testing at 10e -8. Assign the SNP/CNPs to genes; prioritize iti 5 to 10 variants because they are coding or regulatory or all occur in the same gene. Follow-up these variants in replication samples that are 2 to 5 fold larger than the discovery sample. A posteriori use our knowledge from biology to make sense of the finding or do new experiments.
GWAS for Major Depression Case-control association i study on 435.291 SNPs 1738 NESDA CASES Patients with DSM-IV Lifetime Major Depressive Disorder by clinical interview. 1802 NTR HYPERCONTROLS: Subjects not just free of current depression, but very low genetic vulnerability for the disorder (longitudinal genetic factor score). 6079 cases and 5893 controls REPLICATION: from 6 independent samples (Bonn-Mannheim- Muenster/MPI-Munich/ UniversityEdinburgh/ DeCC-UK/ STAR*D-USA/ QIMR-Australia)
PCLO gene Localizes to the presynaptic p active zone of monoaminergic neurons. Coding SNP rs2522833 in exon 17 (ala-4814-ser, MAF 0.45) near the C2A calcium binding domain Replicated in the population-based samples at p < 10e-7
938 trios
Edge piece philosophy Risk for Conduct Disorder 90% Numb ber of pe ersons 60% 30% 0% Liability Aggression 29.3 25.4 21.5 17.6 13.7 9.8 5.9 2 Electrode O1 1 2 3 4 5 6
Twin studies
Adoption