AUTISM SUSCEPTIBILITY

LOCI

K30/K12 Meeting

Ana Isabel Alvarez Retuerto, PhD.

What is Autism?

• Early onset (3 yr, even 18 mth or 1 yr)

• Social & communicative impairments

• Repetitive & stereotype behaviors

• Not a distinct disorder but a spectrum(ASDs or PDD, Rett, Asperger, etc)

• Affectation mild-severe

• Other (Mental Retardat., Fra. X., Seizures,Tuberous Sclerosis, etc.)

Diagnosis

• Diagnostic and Statistical Manual for MentalDisorders (DSM-IV) and International Classif.Diseases (ICD10) (last 15 years)

• Autism Diagnostic Interview (ADI) (Le Couteur et al,

1989) or ADI-R (revised), Autism DiagnosticObservation Schedule (ADOS) (Lord C. et al, 2000).

• Other test (Vineland, Peabody Picture VocabularyTest-PPVT, Raven)

Epidemiology

• Rate of PDDs= 60/10,000 (rates of PDD-

NOS & Asperger vary widely w/ survey)

• Prevalence of Autism= 13/10,000

• Asperger Syndrome= 3/10,000

• Mean Male: Female ratio= 4:1• (Fombonne E. et al, 2005)(34 surveys, 14 countries, published

English)

Autism (Causes & Genetics)(1)

• Heritable complex disorder (Rutter, 2000; Folstein & Rosen-

Sheidley, 2001; Lamb et al, 2002).

• Concordance rate MZ twins 60-95%; DZ twins &

siblings 0% and 10% for autism and ASD (Bailey et

al 1995; Folstein & Rutter 1977; Folstein & Rutter 1988; Ritvo et al 1985;

Steffenburg et al 1989).

• Siblings recurrence risk for autism & ASD 2-4.5%(Chakrabarti & Fombonne 2001; Fombonne 2003; Yeargin-Allsopp et al

2003).

• ASD not a Simplex Mendelian Fashion.

Autism (Causes & Genetics)(2)

• Several loci (3-15) proposed (Pickles et al 1995;

Risch et al 1999).

• Clinical complexity & heterogeneity.

• Genetic heterogeneity (several genes in

different families).

• Environmental influences.

Autism/Genetics

• 5-10% show chromosomal abnormalities

– 15q duplication (1-3%)

– Fragile X (1-3%)

– Sex Chromosomes (1-3%)

• Most case complex genetics (3-15 loci proposed)

– Different genes or interactions might cause same

phenotype (multigenic). Several genes act together to

produce full phenotype (polygenic) and/or with

environment (multifactorial).

Susceptibility Loci Search

• 1) Find chromosomal region by linkage

analysis

• 2) Search gene/s or regions through

association studies.

Genome Scans

• 1) Genome-wide scans using microsatellite

markers.

• Many independent genome-scans

several chromosomal regions

no consistent replication of strong linkage

findings

overlap of some regions in these international

family scans.

Genomic Regions Found

• Figure 1. Chromosomal regions with evidence of linkage in 10 genome-wide scans for ASD susceptibility loci. If a dataset has been expanded and updated in subsequent studies, only the most recent publication has been considered.Results fromeach study are indicated by a letter, followed by ** if MLS>3.6, by * if MLS>2.2, and by 8 if MLS>1.A:AGRE[Yonan et al., 2003]; (a) AGRE2 [Cantor et al., 2005]; (B) [Buxbaum et al., 2001], (C) CLSA [Barrett et al., 1999];(D) Duke [Shao et al., 2002b]; (F) Finland [Auranen et al., 2002]; (I) IMGSAC [Lamb et al., 2005]; (M) [McCauley et al.,2005]; (P) PARIS [Philippe et al., 1999]; (S) Stanford [Risch et al., 1999].(Bacchelli et al 2006)

Overlapping Regions

• Chromosome 2q [IMGSAC 2001, Lamb et al 2005, Philippe et

al 1999, Buxbahum et al 2001, Shao et al 2002].

• Chromosome 7q, “AUTS1”, [Int’l Molecular Genetic

Study Autism Consortium, IMGSAC 1998, 99 fam, MLS=2.53][IMGSAC 2001; Lamb et al 2005, Barret et al 1999, Philippe etal 1999, Risch et al 1999, Liu et al 2001, Alarcon et al 2002 & 2005,Auranen et al 2002, Shao et al 2002, Moloy et al 2005, Shellenberg etal 2006].

• Chromosome 17q [IMGSAC 2001, Yonan et al 2003, Stone et

al 2004, Cantor et al 2005, Lamb et al 2005, McCauley et al 2005]

• Loci found & (# diff. studies): Chr.1p(3), 2q(4),3q(4), 4q(3), 6q(4), 7q(8), 10q(4), 13q(3), 16p(7)& 19p(4)

Collaborative Effort (1)

• Unraveling the pathophysiology of the disorder.

• Genetic contribution & interaction or risk withenvironmental factors.

• Understanding the process, prevention, treatment,interventions.

• FAMILIES PARTICIPATION.

• Difficult family environment & ethical issues.

Collaborative Effort (2)

• Autism Genetic Resource Exchange

(AGRE)(www.agre.org) & Cure Autism Now(www.cureautismnow.org)

• National Institute Mental Health NIMH Human

Genetics Repository. 830 (749 MPX families/4014

indiv (w/ DNA & clinical assesments)

• Molecular Cytogenetics and Karyotype (Dr. L Martin &

Dr. Ledbetter/ Emory Univ.)

• Genome Scans

Cytogenetics

• AGRE, abnormal karyotype=13/544 fam.

(2.38%); Fra.X Mut.= 17/751 fam. (2.26%)

Collaborative Effort

Genome Scans (1)• 1) Columbia Univ. (1a) [110 MPX fam, 335 markers].

Main findings: Broad Diag.: Chr. 5p & Xq. Narrow Diag.:Chr. 19q & Xq. Also 8q & 16p (p< 0.01). (1b) Follow-up156 fam (46more) Chr. 7q, 17q & X. (Liu et al 2001). (1c)345 Sib-pairs(235 new). 408 markers (73 new) Chr. 17q11,5p, 11p, 4q & 8q (p<0.01). (Yonan et al 2003). (1c/d) Chr17q11 (p<0.01), 148 sibships Male-only. (Stone et al2004).

• AGRE + Finnish families, [314 fam (288 AGRE + 26Finnish)], Chr. 1p12q25, 3p24-26, 4q21-31, 5p15-q12,6q14-21, 7q33-36, 8q22-24, 17p12-q21 & 19p13-q13(p<0.05). (Ylisaukko-oja T. et al 2006)

Collaborative Effort

Genome Scans (2)

• 2) CIDR scan, [109 sib-pairs, 400 markers], Chr17q21(p<0.01) MO. Formal replication (Cantor et al2005).

• 3) AGP (Autism Genome Project)(NAAR & NIH)(50centers USA+Europe) [1496 fam/7917 fam. members;~ 10,000 SNPs]. Sugg. Link. 11p12-13 & 15q23-25.3(Narrow Diag. FC: 5p15.33, 9p24.1 & 11p13-12,MO:5q12.3 & 9q33.3 (diff. Locat. From FC). Other:2q (FC), 7q modest link (MO). (AGP Consortium2007).

Endophenotypes/QTL (1)

– 1) QTL WORD, PHRASE, RSB: [152 MPX fam. 335 markers]. WORD

Chr7q35 (p=0.001) & chr11(p=0.013). PHRASE Chr10(p=0.018),

11(p=0.014) & 20 (p=0.011) (Alarcon et al 2002)

– 2) QTL WORD, PHRASE, RSB: [291(152+139 new) MPX fam. 408

markers]. WORD Chr3q (p<0.001) & 17q (p=0.002), chr.7q35. PHRASE

Chr17(p=0.013), chr.3(p=0.04) & chr.16 (p=0.019). RSB Chr.16

(p=0.006) (Alarcon et al 2005)

– 3) QTL Non-verbal Communication. [228 MPX fam., 408 markers].

Chr.1p13-q12(p=0.0001), chr.4q21-25(p=0.0008),chr.7q35(p=0.008),chr8q23-24(p=0.005) and 16p12-13 (p=0.001)( OSA) (Chen et al

2006).

Endophenotypes/QTL (2)

• 4) Linkage/Stratification fam. Lang. Delay [133 MPX

fam, 365 markers] Chr.2,4, 6,7,8 & 9(p<0.05).

Chr.1,10,12,15 & 19 (p<0.01)(WD or PD). (Spence et

al 2005)

• 5) Social Responsiveness Scale (SRS) QTL [99 MPX

fam 408 markers, teacher reported]. Chr.11 & 17

(p<0.01). Also MO (p<0.01) in chr. 11, 17 & chr, 4, 8

& 10 (p<0.01). (Duvall et al 2007)

Association Studies

• A) Illumina= 516 SNPs returned clean in 217 AGRE trios.

16 candidate genes assessed with dense SNP typing on chrs 7 and 17 (Stone et

al 2007). 5 neuroligin familiy members tested. No association found.

(www.agre.org)

• B) Perlegen= 12,500 SNPs typed on 1,000 individuals (333Trios) (MPX fam).

220 trios returned. Chr.5, 7 &17, 51 cand. genes neuronal migration, 31 genes

that escape X-inactivation. Candidate pathways also tested (neuronal migration

& synaptic plasticity). Several genes show association. Overrepresentation of

SNPs found (NRXN1, NRXN3, GABARB3).

• D) Illumina= (SNP Repl. Perlegen Results). 384 SNPs in 330 independent

trios. Analysis ongoing searching for replication of previous reported genes.

(CNTNAP2 QTL & Language Delay) .

• Gene profiling in autistic (Fra.X+Chr,15 dup) cell lines (Nishimura et al 2007)

Ongoing

• Focus on endophenotypes. (Word, Phrase,

RSB, Language impairment, SRS, Head

Circumference, Chr.15q+Fragile-X, etc).

• Infant sibs & Endophenotypes.

• Preparation of 3rd stage replication

(CNPNAP2) AGRE+ other cohorts.

• Imaging & Genetics.(CNTNAP2 & fMRI)

Acknowledgments

• UCLA• Daniel H. Geschwind

• Stanley F. Nelson

• Rita Cantor

• Maricela Alarcon

• Sarah Spence

• Jennifer Stone

• Jackie Duvall

• Gary Chen

• Naoko Kono

• Ake Lu

• AGRE & FAMILIES

• Emory University• Christa L. Martin

• David Ledbetter

• University of

Chicago• T. Conrad Gilliam

• Amanda L. Yonan

• NIH grants R01 MH 64547 and U54

MH068172 to Dr. Daniel H. Geschwind