The Etiology of Human Congenital Heart Defects

Literature Seminar Feb 19 2009

Bernard Thienpont

Congenital Heart Defect

•structural anomaly of the heart, present at birth

•not necessarily manifest in the neonatal period

•can remain benign throughout life

Congenital Heart Disease

Congenital heart defect

(Congenital) Cardiomyopathy (Congenital) Rhythm Disturbance

Congenital Heart Disease

Congenital heart defect

(Congenital) Cardiomyopathy Congenital Rhythm Disturbance

A = Secondary to B

Congenital Heart Disease

Congenital heart defect

(Congenital) Cardiomyopathy Congenital Rhythm Disturbance

A & B share an underlying cause

(same gene independently associated with both)

NKX2.5ACTC

Heart formation

1. heart field specification

van Wijk, Moorman & van den Hoff , 2006

Heart formation

2. Heart tube formation

Moorman & VandenBerg, 2009

Concomitant neural crest induction

Heart formation

3. Heart chamber formation

Moorman & VandenBerg, 2009

Black, 2007

http://pie.med.utoronto.ca/HTBG/HTBG_content/HTBG_heartEmbryologyApp.html

Different chamber identities

Heart formation

4. Outflow tract septation

Black, 2007

Semin Cell Dev Biol. 2007 February; 18(1): 101–110

Black, 2007

Semin Cell Dev Biol. 2007 February; 18(1): 101–110

Heart formation

5. Ventricular septation

Cai et al, nature 2008

Heart formation

5. Atrial septation

CHDs: Classifications

• Why?Many CHDs are complexDifferent patients can have similar CHDs to a

varying extent

CHDs: ClassificationsAnatomical:Group CHDs that affect the

same cardiac structure e.g. AEPC

Abnormalities of : • Position and connection of heart • Tetralogy of Fallot and variants• Great veins• atriums and atrial septum• AV valves and AV septal defect• Ventricles and ventricular septum• VA valves and great arteries• Coronary arteries, arterial duct and

pericardium

Embryological:Group CHDs that are

caused by the same embryological problem

e.g. Boughman et al., AJMG 1987

Abnormalities because of • Cell migration problems• Flow lesions• Cell death• Extracellular matrix• Targeted growth defects• other

e.g. VSDAnatomical:Group CHDs that affect the

same cardiac structure e.g. AEPC

Abnormalities of : • Position and connection of heart • Tetralogy of Fallot and variants• Great veins• atriums and atrial septum• AV valves and AV septal defect• Ventricles and ventricular septum• VA valves and great arteries• Coronary arteries, arterial duct and

pericardium

Embryological:Group CHDs that are caused

by the same embryological problem

e.g. Boughman et al., AJMG 1987

Abnormalities because of • Cell migration problems VSD-I• Flow lesions VSD-II• Cell death VSD-III• Extracellular matrix VSD-IV• Targeted growth defects• other

Frequency of CHDsVSD

ASD

PS

ToF

Coarc

AoS

AVSD

TGA

HLH

DORV

Pulmonary atresia

Ebstein

Single ventricle

TA

TAPVC

Tricuspid valve atresia

Hoffman & Kaplan (2002)

Clinical classification

Isolated vs syndromic CHDs? Second major malformation? Dysmorphism (3 or more minor malformations)

Δ etiology:Mostly multifactorial vs single (genetic) cause

Syndromic vs isolated CHDs

dTGA AS

Ebstein PA AS SV TA

PDAASD

0%10%20%30%40%50%60%70%80%90%

100%

Greenwood (1975) & Pradat et al. (2003)

Causes of CHDs

• Environmental or genetic?

Environmental causes

• Teratogens – Alcohol– α-epileptica

• PKU

Environmental causes

• Teratogens • PKU• Viral infections?

1 2 3 4 5 6 7 8 9 10 11 120.50.60.70.80.9

11.11.21.31.41.5

Environmental causes

• Teratogens• PKU• Viral infections• Pregestational diabetes

Diabetic Non-diabeticCVM 22 1417

Normal 587 1905923.61% 0.74% Major CHDs:TGAPTAAVSD

Environmental causes

• Teratogens• PKU• Viral infections• Pregestational diabetes• Twinning

Twinning

~ chorionic & amniotic structures:DC/DA 1%

Twinning

~ chorionic & amniotic structures:DC/DA 1%MC/DA 5-7% (concordance = 25-50%)

TTT: 8% vs 3.4%

Twinning

~ chorionic & amniotic structures:DC/DA 1%MC/DA 5-7% (concordance = 25-50%)

MC/MA 28% (often right atrial isomerism)

Twin studies

ProblematicMZ : 25-50% concordanceDZ : 13% concordance

discordance?– Postzygotic mutations– Epigenetic Δ (e.g. X inactivation)– Stochastic factors

Catastrophic Chance

– …

Genetic causes

x1.3

x4.3x5

Population risk = 0.8% Relative risk:

Genetic causes

Familial aggregationExcluding BAV

AoS ASD AVSD Coarc HLH PS ToF TGA TA VSD CHD0%

2%

4%

6%

8%

10%

12% SibsParentsChildren

Genetic causes

CHD Frequency in parents of CHD children

AoS ASD AVSD Coarc HLH PS ToF TGA TA VSD CHD0%

1%

2%

3%

4%

5%

6%

7%

8%

Parents

mothers

fathers

Genetic causes

CHD frequency in children of CHD parents

AoS ASD AVSD Coarc HLH PS ToF TGA TA VSD CHD0%

2%

4%

6%

8%

10%

12%

Childrenmother is probandfather is proband

Genetic causes

Familial aggregation: caveats– Ascertainment bias– Mailing questionairs– Inclusion criteria– Classification differences

Genetic causes

Increased transmission of CHD via mother • > Male susceptibility• Mitochondrial?• Imprinting

Classification of genetic causes

• genetic lesionsmall mutations ↔ chromosomal aberrations

• inheritance patternAD, AR, XL, other

• pathogenic mechanism of the mutationLoss-of-function, gain-of-function, dominant-negative

• number of loci involved:monogenic, oligogenic, polygenic

genetic lesion

small mutations ↔ chromosomal aberrations• Based on detection technique• Distinction = blurring

genetic lesion

small mutations • Syndromic / isolated• De novo / familial• Monogenic

• Frequent SNPs

– ELN– CREBBP– NKX2-5

chromosomal aberrations• Syndromic (± 55% of sCHD)• de novo• Often contiguous gene

syndromes• ID = diagnosis

– AVSD in T21– ASD, VSD, PS in 4p-– aortic abnormalities in 45,X

Inheritance pattern: AD

• 37/51 genes that are associated with CHDs– 22/37 loss of function

• signaling molecules• transcription factors• Transcription modulators

– Dominant-negative• Alagille (JAGGED1)• Structural proteins (MYH6, MYH11, ACTC1, …)

– Gain-of-function• Noonan/CFC/Costello• Rarely: TBX5, TBX1

Inheritance pattern: XL

• 6/51: XL• All but ZIC3: syndromic• Turner (45,X)

40%: CVM (L-OFT abn: Coarc, AS, HLH)

Etiology?Pre-X-inactivation? UnlikelyPAR?10% of genes escape X-inactivation

Inheritance pattern: XL

male preponderance:

ASdTGA

HLHCoarc

DORV

TAPVR PA ToFASD

AVSD0%

10%20%30%40%50%60%70%80%90%

100%

femalemale

The number of loci

rela

tive

risk

& e

ffect

size

population frequency

monogenic

oligogenic

polygenic

Monogenic

Most mutations causing iCHDs high penetrance

ascertainment bias !!most genes: linkage studies (necessarily high penetrance)

Monogenic

Variable penetrance & expressivityDue to

Type of mutation (eg TBX5)Modifiers eg VEGF polymorphisms in del22q11 + CHD

CRELD1 mutations in T21 + AVSD

Monogenic

Variable penetrance & expressivityYET:Typical CHDs

eg AVSD in T21conotruncul malformations in del22q11Familial CHDs: high concordance

Oligogenic

• No segregation of mutation with phenotype• Rare & unique mutations• Gene ID: candidate gene approach• Sequencing patients and normal controls• Functional studies

Oligogenice.g. FOXH1, GDF1, CFC1 and TDGF1:27/375 patients carry a mutation vs 0/125 control

Oligogenic

Functional studies

Polygenic

• SNPs that predispose to CHDs• Different constellations:

– Polymorphism in cis on same allele • eg T21

– Polymorphism in cis on other allele • eg del22q11: no SNPs in TBX1 are associated with CHDs

(Rauch 2004)

– Polymorphism in trans• VEGF in 22q11

Polygenic

• Low effect size• likely environmental contribution

Multifactorial (genes + environment)e.g.

SNP in NNMT risk does not increase significantlylow Nicotamide intake risk does not increase significantly

SNP in NNMT + low Nicotamide intake significantly increased risk

Gene identification: Challenges

• Large cohort of different types of CHD• Sequence patients and controls (1000 genomes)

• Include CNV analysis• Functional studies to prove pathogenic nature• Link between CHD and defect in heart

formation is often unclear