soo jeong kim, m.d. department of psychiatry university of ... · asdasd score (shao et al. 2003)....

Soo‐Jeong Kim, M.D.Department of Psychiatry

University of Florida

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Is autism “genetic, i.e., heritable”?

What is the evidence?

What do we know?

What is the mechanism?

What are the barriers in finding “genes” for autism?

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What do we know about neurobiology of autism?

Animal models?

Neuroimaging studies?

Neuroanatomy?

Neurotransmitters?

“Autistic disturbances of affective contact”

Inability to relate to others

Failure to use language to convey meaning

Congenital‐not schizophrenic

Similar trait in the family

Large head circumference

Obsessive desire for sameness

Rituals, routines, repetitive questions

Leo Kanner, 19434

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DSM‐I(1952)

DSM‐III(1980)

DMS‐II(1968)

DSM‐III‐R(1987)

DSM‐IV(1994)

“autism” was first described in 1943, but no mention of autism in DSM‐I

“autistic” was mentioned under the “schizophrenia, childhood type”

“Infantile autism”‐ six criteria; highly specific“Atypical PDD” for other ASDs

“Autistic disorder” requires 8 items; much broader than DSM‐III; highly sensitive; “PDD NOS” for other ASDs

Five categories under PDD including Autism, Asperger, Rett’s, CDD, and PDD NOS

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Social Reciprocity

NonverbalPeer

Sharing

Reciprocity

Communication

Delayed speech

conversation

Odd speech

Pretend play

RRBCircumscribed

Interest

Inflexible routines

Stereotypy

Parts of objects

DSM-IV Diagnostic Criteria for ASDs

Social Communication

Deficits in social‐emotional reciprocity

Deficits in nonverbal communicative behaviors used for social interaction

Deficits in developing and maintaining relationships

RRB

Stereotyped or repetitive speech, motor movements, or use of objects

Excessive adherence to routines

Highly restricted, fixated interests

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Hyper‐or hypo‐reactivity to sensory input or unusual sensory interest

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What does “heritable” mean?

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Heritability: The proportion of observed variation in a particular trait that can be attributed to inherited genetic factors in contrast to environmental factors.

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If genes influence autism, family members show more “autism‐related” behaviors than unrelated people.

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Twin Study

Family Study

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DSM‐III“Autism”SRR=4.5%

ASDSRR=10.9%

Siblings of ASDs –

deficits in communica

tion

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Family Study• Sibling recurrence rate higher than general population• Non‐ASD siblings still show some deficits in communication

Twin Study

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MZ

DZ

SE

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Studies Research Protocol # of Twin Pairs Autism ASD

Folstein and Rutter (1977)

Via letters to psychiatrists

11 MZ, 10 DZSS MZ‐36%DZ‐0%

MZ‐82%DZ‐10%

Ritvo et al (1985)

Advert in autism society newsletter

23 MZ, 10 DZSS, 7 DZOS

MZ‐96%DZ‐24%

Steffenburg et al (1989)

Twin registers and autism society

11 MZ, 10 DZSS, 1 Triplet

MZ‐91%DZ‐0%

MZ‐91%DZ‐30%

Bailey et al (1995)

Folstein and Rutter sample + more

25MZ, 20 DZSS, 2 Triplets

MZ‐60%DZ‐0%

MZ‐92%DZ‐10%

Taniai et al (2008)

Child screening system in Japan

19MZ, 14 DZSS, 12 DZOS

MZ‐95%DZ‐31%

Rosenberg et al (2009)

Interactive Autism Network (IAM)


MZ‐88%DZ‐31%

MZ‐96%DZ‐81%

Lichtenstein et al (2011)

Swedish Twin Registry


MZ‐39%DZ‐15%

Ronald and Hoekstra (2011)

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Twin Study

Family Study• Sibling recurrence rate higher than general population• Non‐ASD siblings still show some deficits in communication

• MZ vs DZ = 36‐96% vs. 0‐31%

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Family & relatives of individuals with ASDs

“mild autism traits” or “broad autism phenotype” are commonly observed

Siblings of ASDs Lower pragmatic language skills

Quantitative autism traits in community sample Continuous distribution

Factor analyses for “triad” of ASD symtoms

Separate genetic factors for RRB vs. Social‐Communication

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How?

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How?

Common variants, e.g. GWAS

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Human Genome Project2003

International HapmapProject2005

Reference human genome sequenceComputerized database

Map of human genetic variations

Chip/bead based SNP array

GWAS

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Human Mol Genetics 2010

1558 autism families1M SNPs on beadchip

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•GWAS revealed several chromosomal loci, some reaching genome‐wide significance level vs. the others suggestive linkage/association

GWAS needs for an extremely high number of families to reach statistical power

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How? Rare variants, e.g. rare mutation or rare CNV


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CNV: Gains or losses of a large chunk of DNA sequence (10 K to 5 M bases).

Science 2007

Increased frequency of de novo CNVs• Simplex 12 out of 118 (0.102)• Multiplex 2 out of 77 (0.026)• All 14 out of 195 (0.072)• Controls 2 out of 196 (0.010)

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Moreno‐De‐Luca et al. Deletion 17q12 is a recurrent copy number variant that confers high risk of autism and schizophrenia. Am J Hum Genet. 2010 Nov 12;87(5):618‐30. Epub 2010 Nov 4. Erratum in: Am J Hum Genet. 2011 Jan 7;88(1):121.

Bremer et al. Copy number variation characteristics in subpopulations of patients with autism spectrum disorders. Am J Med Genet B Neuropsychiatr Genet. 2011 Mar;156(2):115‐24. doi: 10.1002/ajmg.b.31142. Epub 2010 Dec 8.

CNV: 7% in ASD families vs. 1% in control families

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Not necessarily CNV, but any change results in loss/gain of function of specific gene(s)

Kortüm F et al. The core FOXG1 syndrome phenotype consists of postnatal microcephaly, severe mental retardation, absent language, dyskinesia, and

corpus callosum hypogenesis. J Med Genet. 2011 Mar 25.

Fassio A et al. SYN1 loss‐of‐function mutations in ASD and partial epilepsy cause impaired synaptic function. Hum Mol Genet. 2011 Mar 25.

Madrigal I et al. Intermediate FMR1 alleles and cognitive and/or behaviouralphenotypes. Eur J Hum Genet. 2011 Mar 23.

Gauthier J et al. Truncating mutations in NRXN2 and NRXN1 in autism spectrum disorders and schizophrenia. Hum Genet. 2011 Mar 22.

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Kim & Cook 2000

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Genetic syndromes, e.g., 15q11‐q13 mat dup

Genomic imprinting disordersPrader‐Willi syndrome (PWS)

Angelman syndrome (AS)

15q11‐q13

15q11‐q13

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PWSCR

Father Mother

Deletion~70%

mUPD~25%

Imprinting defect <5%

Chromosome 15

15q11‐q13PWSCR

Profound hyperphagia “voracious appetite”

HypotoniaPoor sucking

Failure to thrive

Early‐onset Morbid Obesity Hypogonadism

GH deficiencyShort Stature

Small hands/feet

Almond shaped eyes

Downturned mouth

Almond shaped eyesBitemporal narrowing

Thin upper lipDownturned mouth

RRBASDMood disorder Psychosis

Mild to moderate MR

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PWSPWS

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Increased rate of ASD (18 to 37%) among individuals with PWS, especially with UPD (Veltman et al, 2005).

PWS

SCQ>=15 SCQ<15

Increased linkage at the GABRB3 locus in 15q11‐q13 region in families sharing a high IS factor score (Shao et al. 2003).ASDASD

Genomic imprinting disordersPrader‐Willi syndrome (PWS)

Angelman syndrome (AS)

Microdeletion syndromes22q13 deletion syndrome

Smith‐Magenis syndrome (SMS)

15q11‐q13

15q11‐q13

17p11.2

22q13

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Genomic duplicationDown syndrome

Interstitial maternal dup 15q

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15q11‐q13

Sex chromosome Turner syndrome (45, X) X

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Genetic mutation

Fragile X syndrome (FXS)

Sanfilippo syndrome B

Rett syndrome

Tuberous Sclerosis

17q21

Xq28

Xq27.3

9q,16p

Smith‐Lemli‐Opitz syndrome 11q13

Cohen syndrome 8q22‐q23

ADSL deficiency 22q13.1

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Gene Gene or

Epigenetics

Gene‐Gene or Gene‐Environment interaction‐

Epigenetics


Genetic syndromes, e.g., PWS, 15q11‐q13 mat dup

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Candidate genes

Epigenetics

GWAS

Rare mutation and CNV

Genotype‐Phenotype

Search for common variants

Search for rare variants

SNP chip/bead

Whole genome sequencing and/or

SNP array

Gene‐GeneGene‐Environment

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Clinical heterogeneity is a main barrier to identification of susceptibility genes for ASDs.

Rule out known genetic syndromes

Gold standard instruments for ascertainment

Dissection into intermediate or endo‐

phenotypes

Reduced genetic heterogeneity

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What are the findings from neurobiological studies for ASDs?

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• Early overgrowth of brain: normal or smaller head circumference at birth, followed by increase in the rate of growth beginning at ~12 months.

Head Circumference

• Existing MRI studies showed very young children with autism (18mo‐4yo) have 5‐10% abnormal enlargement in total brain volume.

• Not clear whether this enlargement persists into later childhood and adolescence.

• White matter growth>>Gray matter growth• Largest and most consistent growth reported in the

frontal lobes

Neuroimaging studies

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• Only a few studies with limited number of samples• Cerebral cortex – unusually coarse and poorly

laminated, increased cortical thickness, high neuronal density, neurons present in the molecular layer

Cerebral Cortex

Cerebellum• The size of vermis‐not consistent across studies• Decreased Purkinje cells, less expression of GAD67

mRNA

Amygdala

• Precocious enlargement persisting through late childhood

• Abnormal enlargement associated with more severe anxiety, worse social communication skills.

• Decreased number of neurons‐not consistent

Other brain regions

• Limited study‐enlargement of caudate nucleus associated with RRB

• Abnormal hippocampus‐inconsistent across studies

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Amaral et al. 2008

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Mutant mouse models

Environmental restriction

CNS Insult

Pharmacologicintervention

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Social Communication RRB

Choice test: Time spent in a chamber with a social vs. nonsocial stimuli

Ultrasonic vocalization: distress calls for maternal

intervention

Repetitive movement;

excessive self‐grooming; self‐

injurious behavior

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Engrailed 2 null mouse: Reduction of social play‐chasing, pushing, crawling, sniffing

Fmr1‐null mouse: increased levels of social anxiety, reduced social interaction, hyperactivity, and deficits in spatial learning

Mecp2‐mutant mouse: reduced social approach

Prenatal valproic acid exposure: delayed maturation, decreased social exploration

Shank3‐mutant mouse: Deficits in social interaction

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Nature 2011

46Moy and Nadler, 2008

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Mutant mouse models Model for Rett Syndrome (Mecp2) – repetitive forelimb movement

(Shahbazian et al., 2002) Model for Down syndrome (Ts65Dn) – stereotypy (Turner et al., 2001) Model for Alzheimer (TgCRND8) – stereotypy (Ambree et al., 2006) Hoxb8mutant mice ‐ compulsive self‐grooming (Greer & Capecchi, 2002) Sapap3 KO mice ‐ compulsive grooming (Welch et al., 2007)

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Mutant mouse models Model for Rett Syndrome (MECP2) – repetitive forelimb movement

(Shahbazian et al., 2002) Model for Down syndrome (Ts65Dn) – stereotypy (Turner et al., 2001) Model for Alzheimer (TgCRND8) – stereotypy (Ambree et al., 2006) Hoxb8 mutant mice ‐ compulsive self‐grooming (Greer & Capecchi, 2002) Sapap3 KO mice ‐ compulsive grooming (Welch et al., 2007)

CNS insults Prenatal exposure to valproic acid in rats: locomotor and

repetitive/stereotypic‐like hyperactivity (Schneider & Przewlocki, 2005) Borna disease virus infected rats: dyskinesia (Solbrig et al., 1996) Neonatal lesions to limbic structures in rhesus monkeys: delayed stereotypies

(Bachevalier et al., 1999) Stereotypies and hyperactivity in rhesus monkeys exposed to IgG from

mothers of children with autism (Martin et al., 2008)

Martin et al., 200850

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Pharmacological inductionPharmacological induction Intrastriatally administered DA agonist or glutamate receptor ligand induces stereotypy. Intracortical administration of D2 or GABA antagonist enhances motor effect by DA agonist. Intracortical administration of DA or GABA agonist attenuates drug‐induced stereotypy Expression of RRB may be mediated by cortical‐basal ganglia circuitry

(possibly indirect pathway?)

Environmental restriction Restricted housing environments (e.g., zoo, farm, laboratory,

etc.) Early social deprivation

Induces species‐typical RRB, e.g., crib biting or head shaking in horse, jumping or backward somersaulting in deer mice.

Peromyscus maniculatus (deer mice) Species‐typical stereotypy:

Vertical jumping Backward somersaulting

Lewis lab, personal communication52

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GABA(major inhibitory)

Glutamate (major excitatory)

Dopamine (DA)

Serotonin

Pharmacological studies Intracortical GABA antagonist enhance RRBIntracortical GABA agonist attenuate RRB

Increased linkage at GABRB3 locus in families with high IS (Shao et al., 2003)

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Dopamine (DA)

Serotonin

GRIK2 and GRIN2APositive association with autism

NLGN3 and NLGN4Mutation in two brothers (X‐linked ASD)

NRXN1Rare mutation causing ASD

NRXN3Strong linkage signal to compulsive hoarding among multiplex OCD families with two or more hoarding relatives

SLC1A1 Positive association with OCD

SNP Model of inheritancea Allele Familiesb Sc E(S)d Ze pf

rs301430 Additive C 56 43 42 0.24 0.81

Recessive C 22 8 7 0.47 0.64

T 50 21 21 0.00 1.00

rs301979 Additive C 55 78 71 1.70 0.09

Recessive C 50 24 21.75 0.66 0.51

G 18 1 5.75 ‐2.47 0.01

rs301434 Additive A 59 65 59.5 1.27 0.20

Recessive G 37 11 14.5 ‐1.22 0.22

A 38 17 15 0.69 0.49

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Dopamine (DA)

Serotonin

GRIK2 and GRIN2APositive association with autism

NLGN3 and NLGN4Mutation in two brothers (X‐linked ASD)

NRXN1Rare mutation causing ASD

NRXN3Strong linkage signal to compulsive hoarding among multiplex OCD families with two or more hoarding relatives

SLC1A1 Positive association with OCD

SLC25A12Positive association with ADI‐R D2 in ASD

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Dopamine (DA)

Serotonin

Pharmacological study – induction of stereotypy or self‐mutilation by DA agonist

Animal model – greater invariance in DAT KO mice

Lesch‐Nyhan syndrome – inverse correlation between # of DA nerve terminal and severity of self‐mutilation (Ernst et al., 1996)

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Dopamine (DA)

Serotonin

SLC6A4

• Candidate for autism based on hyperserotonemia & efficacy of SSRIs in treating repetitive behaviors

• Association between novel variants & rigid compulsive behavior (Sutcliffe et al. 2005)

• Association between 5‐HTTLPR long/long genotype & RSMB (Brune et al. 2006)

Pharmacological studies

• Tryptophan depletion worsened repetitive motor behaviors in adults with autism (McDougle et al., 1996)

• Positive correlation between 5‐HT1D receptor sensitivity and baseline compulsion scores in autism (Hollander et al., 2000)

RRB

Arm Flapping

Strict routines

Head banging Focus on parts

Intense preoccupation

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RBS‐R:43 items

Stereotypy

Self injury

Compulsion

Restricted

Sameness

Ritualistic

61Bodfish, Symons & Lewis (2000)

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108 participants with ASDs (Kim lab)

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109 participants with ASDs (Cook lab)

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Lam (n=307) Kim(n=108, RBS=SCQ>14) Cook (n=109)

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Is autism genetic?

Yes, based on family and twin study, autism is highly genetic.

Possibly separate genetic factors responsible for social/communication vs. RRB

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What kinds of genetic studies are ongoing?

GWAS to identify common alleles with small effect sizes

Mutation screening to identify rare mutations

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What is the main barrier to

identify genetic factors?

Clinical and Genetic

heterogeneity

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How to overcome

heterogeneity?

Carefully rule out known genetic syndromes

Utilize rigorous diagnostic assessments

Dissection of phenotypes and examine genotype‐phenotype analyses

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What do we know about brain volume?

Large HC=early childhood brain overgrowth

Frontal lobe >>WM >> GM

Longitudinal study to follow

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What do we know about

neuropathology?

Limited number of studies

Some evidence of abnormalities in Cerebral cortex, cerebellum, amygdala and caudate, etc.

Again, heterogeneity issue

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Animal models?

Transgenic mice to study specific gene mutation

Some interesting models include SHANK3 and SAPAP3 mutant mice.

Environmental factors

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Mark LewisDan DriscollEd Cook

Greg ValcanteAnnette Zaytoun

Cindi FloresRaquel Silva

Judith BadnerSteve Guter

Carlos Sulsona

Families

with PWS

Families with ASDs

&Families with PWS

PWSA (USA)NIMH K23UIC‐ACE P50 HD055751

CTSICARDAPPCI

soo jeong kim, m.d. department of psychiatry university of ... · asdasd score (shao et al. 2003)....

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