Ahmad R. Hariri, Ph.D.

Developmental Imaging Genomics Program

Department of Psychiatry

University of Pittsburgh School of Medicine

Functional Neuroimaging of Genetically Driven Variation in Brain Function:

Towards a Biological Understanding of Individual Differences in Behavior

Why study genes?

• Various aspects of cognition, temperament, and personality are highly heritable (40-70%)

• Account for the lionshare of susceptibility to major psychiatric disorders

• Transcend phenomenological diagnosis, and represent mechanisms of disease

• Offer the potential to identify at-risk individuals and biological pathways for the development of new treatments

Deshaies 02 — DNA Man #1

Genes:multiple

susceptibility alleles each of

small effect

Behavior:complex functional

interactions and emergent

phenomena

How do we get from here to there?

Genes:multiple

susceptibility alleles each of

small effect

The path from here to there…

Cells:Subtle

molecular alterations

Behavior:complex functional

interactions and emergent

phenomena

Systems:response bias to

environmental cues

IMAGING GENOMICSIMAGING GENOMICS

Imaging Genomics:Basic Principles

Imaging Genomics: Basic Principles

1) Selection of candidate genes

– Well defined functional polymorphisms, associated with specific physiological effects at the cellular level in distinct brain circuits

– Genes with identified SNPs or other allele variants with likely functional implications involving circumscribed neuroanatomical systems

Imaging Genomics: Basic Principles

2) Control for non-genetic factors– Systematic differences between genotype groups could

either obscure a true gene effect or masquerade for one

• Age, gender, IQ, population stratification

• Environmental factors such as illness, injury, or substance abuse

• Task performance– Linked pari passu with BOLD response– Match or consider variability

Imaging Genomics: Basic Principles

3) Task selection– Imaging tasks must maximize sensitivity and

inferential value, as the interpretation of potential gene effects depends on the validity of the information processing paradigm

• Engage circumscribed brain circuits

• Produce robust signals in all subjects

• Show variance across subjects

Imaging Genomics: Applications

Slide courtesy of K.P. Lesch

Central serotonergic system

Figure courtesy of K.P. Lesch

Typical 5-HT neuron and target synapse

Figure courtesy of K.P. Lesch

5-HT Transporter Promoter Variant (5-HTTLPR)

The 5-HTTLPR

Genes:Short and long allele variants

Cells:Alterations in synaptic 5-HT

Harm avoidance,Neuroticism, Depression,

Anxiety

5-HTTLPR and temperament

Genes:Short and long allele variants

Cells:Alterations in synaptic 5-HT

Harm avoidance,Neuroticism,Depression,

Anxiety

Systems:amygdala bias to

environmental cues

IMAGING GENOMICSIMAGING GENOMICS

The Amygdala

fMRI amygdala reactivity paradigm

(A.K.A. Hariri’s Hammer)

P < 0.05, corrected

5-HTTLPR S allele driven amygdalahyper-reactivity to environmental cues

Hariri et al., Science 2002

S allele driven amygdala hyper-reactivity

Heinz et al., Nature Neuroscience 2005

Berlin replication in healthy adults

LL LS SS

R=0.6, p<0.005

Bertolino et al., Biological Psychiatry 2005

Italian replication in healthy adults

0,00

0,05

0,10

0,15

0,20

0,25

0,30

ss ls ll

SERT genotype

% S

ign

al C

han

ge

in A

myg

dal

a

P < 0.05, corrected

S carriers > L/L

Pittsburgh replication in healthy adults

5-HTTLPR S carrier > LL(P < 0.05, uncorrected)

Sample Demographics:LL: 8♀/4♂; Mean age = 46.1S carrier: 9♀/7♂; Mean age 47.5

Furmark et al., Neuroscience Letters 2004

Swedish replication in social phobics

NIMH replication in healthy adults

6527N =

5-HTTLPR

S CarrierL/LM

ea

n +

/- 1

SE

M R

igh

t Am

ygd

ala

BO

LD .3

.2

.1

0.0

-.1

N = 92

Hariri et al., Archives (2005)

Elaboration: S allele load and sex effects

92313 52814N =

5-HTTLPR

S/SL/SL/L

Mea

n +

/- 1

SE

M R

ight

Am

ygda

la B

OLD

.3

.2

.1

0.0

-.1

SEX

Female

Male

Hariri et al., Archives (2005)

5-HTTLPR and temperament

Genes:Short allele

variant

Cells:Increased

synaptic 5-HT

?????????

Systems:amygdala bias to

environmental cues

IMAGING GENOMICSIMAGING GENOMICS

Amygdala reactivity and harm avoidance

Right Amygdala BOLD

.8.6.4.20.0-.2-.4-.6-.8

Tot

al H

arm

Avo

idan

ce

30

20

10

0

-10

Left Amygdala BOLD

.8.6.4.2-.0-.2-.4-.6

Tot

al H

arm

Avo

idan

ce

30

20

10

0

-10

* No correlation between amygdala reactivity and HA

Prefrontal-Amygdala Dynamics

Wood & Grafman 2003

Reduced functional coupling of the amygdala and prefrontal cortex in S allele carriers

Pezawas et al. Nature Neuroscience 2005

right

left

Overall Coupling 5-HTTLPR Effects

Amygdala-Prefrontal connectivity predicts HA

Functional circuitry is key for understanding complex emergent phenomena

Hamann Nature Neuroscience 2005

5-HTTLPR biases corticolimbic information processing related to temperament

Subgenual PFC 5-HT1A and 5-HT2A binding predict amygdala reactivity

sgPFC 1A/2A ratio predicts amygdala reactivity

DRN 5-HT1A predicts amygdala reactivity

Figure courtesy of K.P. Lesch

Typical 5-HT neuron and target synapse

hTPH2 G(-844)T polymorphism

• Relatively high minor allele frequency (T allele = 38%)

• Located within 1 Kb (844 bp upstream) of the transcription initiation site of hTPH2 and is likely a constituent of the proximal promoter of the gene

• Regulatory variants often produce functional changes in gene expression

• Transcriptional regulatory databases indicate transcription factor recognition sequence homology surrounding the -844 promoter variant (http://www.genomatix.de)

• In silico evidence that the G to T allele substitution potentially modifies the binding of several transcription factors including octamer-binding factor 6, special AT-rich sequence-binding protein 1 as well as homeodomain proteins MSX-1 and MSX-2

hTPH2 G(-844)T biases amygdala reactivity

-1.00

0.00

1.00

2.00

hTPH2 genotypeG/G T carrier

Rig

ht

amyg

dal

a ac

tivi

ty

(in

arb

itra

ry u

nit

s)T carriers > G/G

Brown et al., Molecular Psychiatry (in press)

hTPH2 G(-844)T biases amygdala reactivity

Genes:hTPH2

expression?

Cells:5-HT synthesis?

EmotionalBehaviors?

Systems:amygdala bias to

environmental cues

"

"

Acknowledgments

University of PittsburghSteve Manuck

Bob FerrellCarolyn Meltzer

Sarah BrownPatrick FisherScott Kurdilla

NIMH - GeCaPDanny Weinberger

Emily DrabantKaren MunozAnand Mattay

Lukas PezawasAndreas Meyer-Lindenberg

Support:NIMH P01MH041712-18, R24MH067346-03, R01MH061596-04; NIDA R01DA018910-01; NARSAD