HRC2009, Birmingham, October 20th 2009
Transcript of HRC2009, Birmingham, October 20th 2009
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Genet ic Bas is o f Cl in ic a l Ar rhyt hm ias
Andrew Grac ePapw or t h Hospi t a l and Cam br idge Univers i t y
HRC2009, Bi rm ingham , Oc t ober 20 t h 2009
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The Human as an Experimental System
in Molecular Genetics
The core of genetics is to screen for mutations that causedetectable, heritable changes in biological form orfunction
Ray White, Science1988
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The Human as an Experimental System
in Molecular Genetics
The core of genetics is to screen for mutations that causedetectable, heritable changes in biological form orfunction
Human genes have historically been identified whenaffected by mutations producing genetic disease
Ray White, Science1988
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Long QT Syndrome
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Long QT Syndrome
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Monogenic DisordersSimple Mendelian disorders caused by ~1000 Disease-causing genes
e.g. Hypertrophic cardiomyopathy, Long-QT syndrome, Brugada
syndrome etc.
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Characterisation monogenic diseases
1. Careful phenotyping
2. Genotyping: positional cloning, candidate gene
3. Genetic modifiers
Monogenic DisordersSimple Mendelian disorders caused by ~1000 Disease-causing genes
e.g. Hypertrophic cardiomyopathy, Long-QT syndrome, Brugada
syndrome etc.
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Gene Mutation Arrhythmia Substrate
ARRHYTHMIAS AND GENETIC HEART DISEASE
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Gene Mutation Arrhythmia Substrate
ARRHYTHMIAS AND GENETIC HEART DISEASE
Ion channel
MutationTorsade de Pointes
Direct Relationship: Long QT SyndromeSarcomere
MutationVentricularFibrillation
Indirect Relationship e.g. Hypertrophic Cardiomyopathy
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Gene Mutation Arrhythmia Substrate
ARRHYTHMIAS AND GENETIC HEART DISEASE
Ion channel
MutationTorsade de Pointes
Direct Relationship: Long QT SyndromeSarcomere
MutationVentricularFibrillation
Indirect Relationship e.g. Hypertrophic Cardiomyopathy
StructuralDisorganization
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Gene Mutation Arrhythmia Substrate
ARRHYTHMIAS AND GENETIC HEART DISEASE
Ion channel
MutationTorsade de Pointes
Direct Relationship: Long QT SyndromeSarcomere
MutationVentricularFibrillation
Indirect Relationship e.g. Hypertrophic Cardiomyopathy
StructuralDisorganization
Ion channelMutation
Ventricular Fibrillation
Putative Direct Relationship e.g. Brugada Syndrome
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Mutations in Cardiac Ion Channel Genes responsiblefor Cardiac Arrhythmias
Priori and Napolitano Ann NY Acad Sci 2004; 1015:96-110
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Considerations specific to humans Highest order experimental system for genetics
Powerful documentation of phenotypes
Expert phenotypers (doctors), records over time- room for improvement
Ray White, Science1988
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Considerations specific to humans Highest order experimental system for genetics
Powerful documentation of phenotypes
Expert phenotypers (doctors), records over time- room for improvement
BUT not the best experimental system for intervention
- overlong generation time, social proscriptions tocontrolled crosses etc.
Ray White, Science1988
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GM mice as the functional bridge:
technical issues
Modification technique
GM > Dominant Negative
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GM mice as the functional bridge:
technical issues
Modification technique
GM > Dominant Negative
Choice of gene
Scn5a, RyR2> K channels
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GM mice as the functional bridge:
technical issues
Modification technique
GM > Dominant Negative
Choice of gene
Scn5a, RyR2> K channels
Method of Interrogation
Physiological range (HR >550) Translational (mouse/human) Comprehensive physiological,structural and molecular assays
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GM Mouse Models of Cardiac Arrhythmias(Cambridge Group)
Scn3b
B d S d ECG d V t i l A h th i
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50
100
012 36 72 96
ICD
Drugs
No Rx
Time [months]
% SurvivalLogrank = 0.0005
Survival according to treatment (n=63)
Brugada et al. Circulation 1998;97:457-60
Brugada Syndrome: ECG and Ventricular Arrhythmias
V1
V2
07.1998
01.2000
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Brugada Syndrome: SCN5A Mutations
Association first described 1998
SCN5A: TTX-insensitive sodium channel, 28 exons, 80 kb
Four homologous domains, each 6 membrane spanning segmen
Brugada mutations(> 120) are loss-of-function
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a
bprobe
E P P HBH 32
GFP NEO
c
B 3H
TK
B
a
probe
E P P HBH 3GFP NEO
c
HB
8.0 kb8.8 kb
+/+ +/- -/-Ac t i
Scn5
GFP
Proc Natl Acad Sci USA. 2002;99:6210
GM MOUSE MODEL
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Wild-type (n=37 9 pA/pF
Scn5a+/-(n=21 5 pA/pF
HALF THE SODIUM CHANNELS
Proc Natl Acad Sci USA. 2002;99:6210-and Leoni et al. submitted 2009
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S1
S1 S2
S
V V
V V
*
*
+/25 ms 25 m
WILD-TYPE MUTANT (Scn5a+/-)
SLOW CONDUCTION
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S1 S2
* * * ** *** ** * ** * S1 S2S1 S2
50
S1 S1 S1S1S1 S1 S1S2 S1S1 S1S2S1 S1S1 S1S1S1 S1 S2
50 ms
Wild-type
Scn5a+/-
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GENES AND FUNCTION (Brugada Syndrome)
SCN5AMutations
SodiumChannels
Ventricular
Arrhythmias
Slowed
Conduction
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GM Mouse Scn5aphenotypes
1. Long QT syndrome (2005-2007) - KPQ 1505-15072. Brugada/idiopathic VF (2002-2007)
3. Lev-Lengre disease/atrioventricular block (2002-2007)
4. Sinus node dysfunction (2002, 2005)5. Atrial arrhythmias (2007)
6. Dilated Cardiomyopathy - but structural change (2005-200
7. Population based risk: SCD, SIDS, drugs (2007)
Interstitial fibrosis in old Scn5a+/ mutants
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OLD WT
OLD HZ
Interstitial fibrosis in old Scn5a+/-mutants
Van Rijen et al. Circulation 2005; 112:1927-193
Intrauterine lethality in Scn5a / mutants
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EC 10.5
Intrauterine lethality in Scn5a -/-mutantsFailure of ventricular development
Scn5a +/-
Scn5a -/-
Intrauterine lethality in Scn5a / mutants
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Scn5a -/-Scn5a +/-
Proc Natl Acad Sci USA. 2002;99:6
Intrauterine lethality in Scn5a -/-mutantsFailure of ventricular development
C l Di S d
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Complex Disease Syndromes
Phenotypes not exhibiting classic Mendelianrecessive or dominant inheritance attributable to a
single gene locus
Practical difficulties
Incomplete penetrance and phenocopy
Genetic heterogeneityPolygenic inheritance
C l Di S d
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Complex Disease Syndromes
Phenotypes not exhibiting classic Mendelianrecessive or dominant inheritance attributable to a
single gene locus
Practical difficulties
Incomplete penetrance and phenocopy
Genetic heterogeneityPolygenic inheritance
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SUBSTRATE FOR ATRIAL FIBRILLATION
MUSCULATURE OF THE PULMONARY VEINS
Nathan and Eliakim; Circulation 1966; 34:412 Ho et al; Heart 2001; 265-270
ASSOCIATION STUDIES
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ASSOCIATION STUDIES
Indirect
Direct
** *
An analogy may help to explain thisphenomenon. In the mid-1960s, George Harrison,Paul McCartney, John Lennon, and Ringo Starr wereoften found together. If you looked for Harrison, there
was a high likelihood, but not complete certainty, thatyou would find the other members of the Beatles ..
SINGLE NUCLEOTIDE POLYMORPHISMS SNPs
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SINGLE NUCLEOTIDE POLYMORPHISMS - SNPs
IN THE GENOME:
~ 90% of all variants
~ 1 SNP / 1.25 kb between any two genomes
~ 2.5 million variants between two genomes
...GCTCCGTTT......GCTCTGTTT...
IN THE EXONS:
~ 60 - 120,000 variants / person
~ 20 - 40,000 non-conservative 1- 2 / gene / perso
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Genome-wide association scan with replication in other populations
Gudbjartsson et al., Nature 2007; 448:353-357
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Genome-wide association scan with replication in other populations
Gudbjartsson et al., Nature 2007; 448:353-357
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Genome-wide association scan with replication in other populations Variants adjacent to PITX2- critical function in left-right asymmetry in heart
Pitx2cplays key role in determination pulmonary myocardiumGudbjartsson et al., Nature 2007; 448:353-357
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SUBSTRATE FOR ATRIAL FIBRILLATION
MUSCULATURE OF THE PULMONARY VEINS
Nathan and Eliakim; Circulation 1966; 34:412 Ho et al; Heart 2001; 265-270
ARRHYTHMIAS AND GENETIC HEART DISEASE
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Gene Mutation Arrhythmia Substrate
ARRHYTHMIAS AND GENETIC HEART DISEASE
Putative
Mutation Ventricular Arrhythmia
ARRHYTHMIAS AND GENETIC HEART DISEASE
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Gene Mutation Arrhythmia Substrate
ARRHYTHMIAS AND GENETIC HEART DISEASE
Putative
Mutation Ventricular Arrhythmia
GENETIC/ENVIRONMENTAL MODIFIERS
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Founder Effect (1730) KCNQ1 (A341V)
Variable significant risk
Non-carrier(n = 154)
A341V-Carrier(n = 166)
430
msec
680msec
Circulation 2005;112:2602-1
Genetic Basis of Clinical Arrhythmias: where nex
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Genetic Basis of Clinical Arrhythmias: where nex
Genotype (high-throughput) Complex disease
Genetic modifiers
Genetic Basis of Clinical Arrhythmias: where nex
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y
Genotype (high-throughput) Complex disease
Genetic modifiers
Phenotype
Mechanisms (mice) Mechanisms (Stem Cell Models)
iPS Cells linking genes to function (2008- )
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CARDIAC
PHENOTYPING CLINICAL MUTATIONDETECTION
PHYSIOLOGY(mapping, confocal
EM, patch clamp etc.)
iPS Cells
iPS Cells linking genes to function (2008- )
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CARDIAC
PHENOTYPING CLINICAL MUTATIONDETECTION
PHYSIOLOGY(mapping, confocal
EM, patch clamp etc.)..human modelsof human disease..
Chien, Nature 2008 453:30
iPS Cells
P di t d li i l b fit f ti
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Predicted clinical benefits of a genetic
description of disease
New taxonomy of disease: mechanisms > phenotype
Predisposition phenotypes e.g. pharmacogenomics
P di t d li i l b fit f ti
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Predicted clinical benefits of a genetic
description of disease
New taxonomy of disease: mechanisms > phenotype
Predisposition phenotypes e.g. pharmacogenomics
Rational drug development
Rational targeting of therapies: drugs, surgery, device
Predicted clinical benefits of a genetic
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Predicted clinical benefits of a genetic
description of disease
New taxonomy of disease: mechanisms > phenotype
Predisposition phenotypes e.g. pharmacogenomics
Rational drug development
Rational targeting of therapies: drugs, surgery, device
Implementation will be problematic