Transcript New genetic tools reveal insights into Huntington`s disease and

New genetic tools reveal insights
into Huntington’s disease and
Autism
Marcy E. MacDonald, Ph.D.
James F. Gusella, Ph.D.
Freemasons Travelling Scholars
CENTER FOR HUMAN
GENETIC RESEARCH
Huntington’s Disease
• Affects about 1 in 10,000
people
• Inherited
• Brain cells die
• Mid-life onset of progressive
movement disorder
• Intellectual decline,
psychiatric symptoms
• Debilitation and early death
• No treatment to prevent or
delay
The view from genetics:
Huntington’s Disease is caused by a difference within
the 3 billion letters of the DNA code that is always
inherited by people who get the disease but not by
people who do not get the disease
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6
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13
14
19
20
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8
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15
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X
18
Y
HD mutation
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HD mutation
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The HD Mutation
Normal HD Gene
AAGCCTTTC-----(CAG)6-35------CAACAGCCG
TTCGGAAAG-----(GTC)6-35------CTTGTCGGC
Mutant HD Gene
AAGCCTTTC-----(CAG)>36-------CAACAGCCG
TTCGGAAAG-----(GTC)>36-------CTTGTCGGC
The HD Mutation
Normal HD Gene
AAGCCTTTC-----(CAG)6-35------CAACAGCCG
TTCGGAAAG-----(GTC)6-35------CTTGTCGGC
Mutant HD Gene
AAGCCTTTC-----(CAG)>36-------CAACAGCCG
TTCGGAAAG-----(GTC)>36-------CTTGTCGGC
Silence the mutant gene
Safety trial
IONIS Pharmaceuticals, Roche Pharmaceuticals
Disease as a lifelong process
Lifeline of a person with a normal HD gene
Conception
Death
Conception
Death
Clinical Diagnosis
Lifeline of a person with the HD mutation
Many people develop symptoms earlier or later than
may be expected for their CAG mutation size
Symptoms 20 years
later than expected
Symptoms 20 years
earlier than expected
Idealized Example of a Successful
HD Clinical Trial
Clinical Diagnosis
Conception
With CAG43
Death
No Intervention
Clinical Diagnosis
Conception
With CAG43
Death
Intervention
People are all different, largely due to
differences in their DNA letters (sequence)
All cases of HD are caused by CAG >36 mutation
in the HD gene
The HD mutation is expressed on the
background of a different 3 billion letter genome
in each individual so symptoms can differ even
in individuals with the same size CAG mutation
New tools to query the differences in the 3
billion letters of your DNA (and thousands of
other people too) all at once
Allele Frequency
0.05
Polymorphism
0.50
High-frequency
Low-frequency
0.0005
Private
0.005
Private
Common variant
single nucleotide
polymorphism
(SNP) arrays:
Indirect detection of
functional variation
Rare variant SNP arrays
Exome sequencing
Indirect and direct
detection of functional
variation
Exome sequencing
Whole genome
sequencing
Direct detection of Exome and genome sequencing
functional variation
Significance
Search the 3 billion letters of the DNAs from 4,000 HD
individuals to find the variant letters that appear together with
earlier or later onset of symptoms, more often than can be
expected by chance
Chromosome
Genome wide association study - GWAS
HD mutation
Good modifier
3
4
Bad modifier
8
Bad modifier
Good modifier
15
Idealized Example of a Successful
HD Clinical Trial
Clinical Diagnosis
Conception
With CAG43
Death
No Intervention
Clinical Diagnosis
Conception
With CAG43
Death
Intervention
Modifier genes – Chromosomes 3, 8 and 15
Need to find the exact letters that are different and
how each difference alters the rate of the disease
process that leads to symptoms
HD as a Genetic Disease –
a lifelong process that is modifiable
before symptoms appear
Conception
Death
Clinical Diagnosis
Conception
Death
Clinical Diagnosis
Conception
Death
Clinical Diagnosis
Investigators and HD family members in:
HD MAPS
PREDICT-HD
COHORT
REGISTRY
World-wide HD registry ENROLL-HD
Autism Spectrum Disorders
• Neurodevelopmental disorders involving social
deficits and communication difficulties, stereotyped or
repetitive behaviors and interests, sensory issues,
and in some cases, cognitive delays.
• Can vary in overall severity and in severity of
individual features --- from mild to extreme.
• Often associated with other developmental disorders
• U.S. estimates as high as 1 in 68 children with males
greatly exceeding girls
CHROMOSOMAL TRANSLOCATION
Two individual with extreme
phenotypes on the autism spectrum
DGAP123:
Mentally impaired female with ritualized behaviors, vocal
and motor mannerisms, limited eye contact, minimal
verbal output, little change in affect or facial expression,
and minimal seeking of interaction.
DGAP200:
Male with pervasive developmental delay- not otherwise
specified (PDD_NOS), attention deficit hyperactivity
disorder (ADHD), conduct disorder with early onset,
and intermittent explosive disorder.
Balanced
chromosome
rearrangements
can pinpoint
genes causing
autism spectrum
disorders
Two individual with extreme
phenotypes on the autism spectrum
DGAP123:
Mentally impaired female with ritualized behaviors, vocal
and motor mannerisms, limited eye contact, minimal
verbal output, little change in affect or facial expression,
and minimal seeking of interaction.
DGAP200:
Male with pervasive developmental delay- not otherwise
specified (PDD_NOS), attention deficit hyperactivity
disorder (ADHD), conduct disorder with early onset,
and intermittent explosive disorder.
In both cases the chromosome rearrangement breaks the gene
NRXN1, involved in interaction and communication between the
surfaces of nerve cells in the brain
More examples of severely affected
individuals
NDR26867 (46,XX,t(3;14)(q25.31;q11.2)dn):
Mentally impaired female with Autism Spectrum Disorder,
precocious puberty, large head size, prominent forehead,
shallow eye ridges, prominent eyes, and posteriorly
rotated ears. Normal MRI.
NDR27031 and NDR27032 (46,XY,t(3;18)(q13.32;q21.2)dn) :
Identical twin boys with global developmental delay. Nonverbal at 27 months of age, could not crawl or stand,
enlarged head size, prominent forehead, posteriorly rotated
ears. Abnormal MRI.
More examples of severely affected
individuals
NDR26867 (46,XX,t(3;14)(q25.31;q11.2)dn):
Mentally impaired female with Autism Spectrum Disorder,
precocious puberty, macrocephaly, prominent forehead,
shallow supraorbital ridges, prominent eyes, and posteriorly
rotated ears. Normal MRI.
The chromosome rearrangement breaks the gene CHD8
NDR27031 and NDR27032 (46,XY,t(3;18)(q13.32;q21.2)dn) :
Identical twin boys with global developmental delay. Nonverbal at 27 months of age, could not crawl or stand,
enlarged head size, prominent forehead, posteriorly rotated
ears. Abnormal MRI.
The chromosome rearrangement breaks the gene TCF4
Both CHD8 and TCF4 are involved in regulating the timing and
degree of expression of large numbers of other genes
Another kind of rearrangement:
microdeletion or microduplication
Gene
discovery
from single
unique
genomes
Talkowski et al., 2012, Cell
Pathogenesis and clinical expression
Disease
Trigger
End-stage
disease
Overt Clinical
Disease
Steps in the Presymptomatic Disease Process
Factors
contributing to
disease
susceptibility
Steps in Disease Progression
Individual
Disease
Features
New Tools for Studying Human Disease Biology:
Patient-Specific Stem Cells
2-3 weeks
grow skin
cells
4-6 weeks
Reprogram
to create
pluripotent
stem cells
3-4 weeks
Develop
mature cells
Cryopreserved
(Cell Bank)
Neural
Differentiation
CRISPR/Cas Genome Modification
Sequencing of Unique Individuals
• Structural analysis and genome sequencing have
revealed many strong effect genes that contribute
to autism spectrum disorders
• Discovery of specific sequence changes has
offered new diagnostic potential for individual
families
• Multiple genetic triggers discovered from
individuals with overlapping manifestations offers
hope of defining shared biological pathways that
lead to individual features of the autism spectrum
• New genetic tools allow not only discovery of
genetic changes but analysis of their effects in
human cells in the laboratory
Thanks to:
If you would like to participate:
mindsforminds.org.nz
Thanks for your attention