2015 bioc4010 lecture1and2
TRANSCRIPT
Next-Generation Sequence Analysis for Biomedical Applications
BIOC 4010/5010
Lecture 1
Dr. Dan Gaston
Postdoctoral Fellow Department of Pathology
Dr. Karen Bedard Lab
Overview: Lecture 1
• Why Next-Gen Sequencing Matters
• What is Next-Gen Sequencing
• Bioinformatics Workflows
• Types of Next-Gen Experiments
• Working with the Human Genome
• Slides available on slideshare:
– http://www.slideshare.net/DanGaston
Major Areas in Human Disease Genomics
• Complex Disease– Genome Wide Association Studies (GWAS)
• Mendelian Disease– Whole Genome/Exome Sequencing
– Transcriptomics
– Genetic Linkage – Sanger Sequencing
• Cancer– Tumour Genomics
– Transcriptomics
Traditional Diagnosis of Genetic Disease
• Genetic Counselors/Physicians order individual testing of genes based on patient phenotype
• For rare diseases or unusual phenotypes may run tens to hundreds of tests
• …..EXPENSIVE (Easily thousands of dollars)
Next Generation Diagnosis of Genetic Disease
• NGS-Based Targeted Sequencing Panels
• Clinical Exome
• Clinical Genome
Cutis Laxa
• Linked Genomic Region ~13Mb in size
• Contains 143 Genes
• Prioritize and select genes for individual sanger sequencing
• …Slow
• …Laborious
• …Can be expensive
Human Genomics: More Power!
• $5,000 - $10,000 to sequence whole genome
– Dropping towards $1000 for sequencing only
• ~$1000 to sequence only protein-coding portion (exome, later)
Clinical Genomics
• Rapid diagnosis of genetic disease in NICU cases
• Quicker and cheaper than sequential genetic testing (traditional method)
Personalized Medicine: Oncology
Tumour SampleDNA
Non-Tumour Sample
DNA
Databases and Annotations
Sequence
Tumour Specific
Mutations
Tumour Classification
Drugs
Genomic ContentChromosome Base pairs Variations Confirmed proteins Putative proteins Pseudogenes miRNA rRNA Misc ncRNA
1 249,250,621 4,401,091 2,012 31 1,130 134 66 106
2 243,199,373 4,607,702 1,203 50 948 115 40 93
3 198,022,430 3,894,345 1,040 25 719 99 29 77
4 191,154,276 3,673,892 718 39 698 92 24 71
5 180,915,260 3,436,667 849 24 676 83 25 68
6 171,115,067 3,360,890 1,002 39 731 81 26 67
7 159,138,663 3,045,992 866 34 803 90 24 70
8 146,364,022 2,890,692 659 39 568 80 28 42
9 141,213,431 2,581,827 785 15 714 69 19 55
10 135,534,747 2,609,802 745 18 500 64 32 56
11 135,006,516 2,607,254 1,258 48 775 63 24 53
12 133,851,895 2,482,194 1,003 47 582 72 27 69
13 115,169,878 1,814,242 318 8 323 42 16 36
14 107,349,540 1,712,799 601 50 472 92 10 46
15 102,531,392 1,577,346 562 43 473 78 13 39
16 90,354,753 1,747,136 805 65 429 52 32 34
17 81,195,210 1,491,841 1,158 44 300 61 15 46
18 78,077,248 1,448,602 268 20 59 32 13 25
19 59,128,983 1,171,356 1,399 26 181 110 13 15
20 63,025,520 1,206,753 533 13 213 57 15 34
21 48,129,895 787,784 225 8 150 16 5 8
22 51,304,566 745,778 431 21 308 31 5 23
X 155,270,560 2,174,952 815 23 780 128 22 52
Y 59,373,566 286,812 45 8 327 15 7 2
mtDNA 16,569 929 13 0 0 0 2 22
FastQ Quality Scores
Quality Score (Q) Probability of incorrect base call Base call accuracy
10 1 in 10 90%
20 1 in 100 99%
30 1 in 1000 99.90%
40 1 in 10000 99.99%
50 1 in 100000 100.00%
Q = -10 log10 P
General Genomics Workflow
Quality Control of Raw
Data
Raw Data
Analysis
Alignment to reference
genome
Whole Genome
Mapping
Detection of genetic variation
(SNPs, Indels, SV)Variant Calling
Linking variants to biological
informationAnnotation
Find the Location of Each Read in the Genome
• Problems:
– Short sequence
– Millions of short sequences
Find the Location of Each Read in the Genome
• Problems:
– Short sequence
– Millions of short sequences
– Big genome
Find the Location of Each Read in the Genome
• Problems:
– Short sequence
– Millions of short sequences
– Big genome
– Mismatches
• Polymorphisms
• Sequencing errors
Find the Location of Each Read in the Genome
• Problems:
– Short sequence
– Millions of short sequences
– Big genome
– Mismatches
• Polymorphisms
• Sequencing errors
– Insertions and deletions
Find the Location of Each Read in the Genome
• Problems:– Short sequence
– Millions of short sequences
– Big genome
– Mismatches• Polymorphisms
• Sequencing errors
– Insertions and deletions
– May be processing many (100’s) of individuals
Short Read Mapping
…CCATAGGCTATATGCGCCCTATCGGCAATTTGCGGTATAC…
GCGCCCTAGCCCTATCGGCCCTATCG
CCTATCGGACTATCGGAAA
AAATTTGCAAATTTGC
TTTGCGGTTTGCGGTA
GCGGTATA
GTATAC…
TCGGAAATT CGGTATAC
TAGGCTATAAGGCTATATAGGCTATATAGGCTATAT
GGCTATATGCTATATGCG
…CC…CC…CCA…CCA…CCAT
ATAC…C…C…
…CCAT
1) Report location of genome where read matches best2) Minimize mismatches3) Mismatches with lower quality bases better than
mismatches with higher quality bases
Short Read Mapping: Brute Force Method (Stupid)
Simple conceptually: Compare each query k-mer to all k-mers of genome
Scales with size of the genome and the reads (Not particularly well)
Genome = AGCATGCTGCAGTCATGCTTAGGCTA
Read = GCT
Solution
Index the Reference Genome
Indexing the reference is like constructing a phone book, quickly move towards the relevant portion of the genome and ignore the rest.
Suffix ArraySplit genome into all suffixes (substrings) and sort alphabetically
Allows query to be searched against an alphabetical reference, skipping 96% of the genome
Ex: banana$banana$ $anana$ a$nana$ ana$ana$ anana$na$ banana$a$ nana$$ na$
Short Read Alignment: Binary Search
• Searching the index efficiently is still a problem…
Index # Sequence Pos Pos
1 ACAGATTACC… 6
2 ACC… 13
3 AGATTACC… 8
4 ATTACAGATTACC… 3
5 ATTACC… 10
6 C… 15
7 CAGATTACC… 7
8 CC… 14
9 GATTACAGATTACC… 2
10 GATTACC… 9
11 TACAGATTACC… 5
12 TACC… 12
13 TGATTACAGATTACC… 1
14 TTACAGATTACC… 4
15 TTACC… 11
Search for GATTACA…
Short Read Alignment: Binary Search
• Searching the index efficiently is still a problem…
Index # Sequence Pos Pos
1 ACAGATTACC… 6
2 ACC… 13
3 AGATTACC… 8
4 ATTACAGATTACC… 3
5 ATTACC… 10
6 C… 15
7 CAGATTACC… 7
8 CC… 14
9 GATTACAGATTACC… 2
10 GATTACC… 9
11 TACAGATTACC… 5
12 TACC… 12
13 TGATTACAGATTACC… 1
14 TTACAGATTACC… 4
15 TTACC… 11
Search for GATTACA…
Short Read Alignment: Binary Search
• Searching the index efficiently is still a problem…
Index # Sequence Pos Pos
1 ACAGATTACC… 6
2 ACC… 13
3 AGATTACC… 8
4 ATTACAGATTACC… 3
5 ATTACC… 10
6 C… 15
7 CAGATTACC… 7
8 CC… 14
9 GATTACAGATTACC… 2
10 GATTACC… 9
11 TACAGATTACC… 5
12 TACC… 12
13 TGATTACAGATTACC… 1
14 TTACAGATTACC… 4
15 TTACC… 11
Search for GATTACA…
Short Read Alignment: Binary Search
• Searching the index efficiently is still a problem…
Index # Sequence Pos Pos
1 ACAGATTACC… 6
2 ACC… 13
3 AGATTACC… 8
4 ATTACAGATTACC… 3
5 ATTACC… 10
6 C… 15
7 CAGATTACC… 7
8 CC… 14
9 GATTACAGATTACC… 2
10 GATTACC… 9
11 TACAGATTACC… 5
12 TACC… 12
13 TGATTACAGATTACC… 1
14 TTACAGATTACC… 4
15 TTACC… 11
Search for GATTACA…
Short Read Alignment: Binary Search
• Searching the index efficiently is still a problem…
Index # Sequence Pos Pos
1 ACAGATTACC… 6
2 ACC… 13
3 AGATTACC… 8
4 ATTACAGATTACC… 3
5 ATTACC… 10
6 C… 15
7 CAGATTACC… 7
8 CC… 14
9 GATTACAGATTACC… 2
10 GATTACC… 9
11 TACAGATTACC… 5
12 TACC… 12
13 TGATTACAGATTACC… 1
14 TTACAGATTACC… 4
15 TTACC… 11
Search for GATTACA…
Binary Search
• Initialize search range to entire list
– mid = (hi+lo)/2; middle = suffix[mid]
– if query matches middle: done
– else if query < middle: pick low range
– else if query > middle: pick hi range
• Repeat until done or empty range
Applied to Human Genome
• In practice simple methods of indexing the genome can create very large data structures
– Suffix Array: > 12 GB
• Solution: Apply complex procedures that allow you to index and compress the data:
– Burrows-Wheeler Transform
– FM-Index
Burrows-Wheeler Transform
• Similar in many ways to creation of Suffix Array
BANANA$
BANANA$ANANA$BNANA$BAANA$BANNA$BANAA$BANAN$BANANA
CircularPermutation
Burrows-Wheeler Transform
• Similar in many ways to creation of Suffix Array
BANANA$
BANANA$ANANA$BNANA$BAANA$BANNA$BANAA$BANAN$BANANA
$BANANAA$BANANANA$BANANANA$BBANANA$NA$BANANANA$BA
LexicographicalSort
Burrows-Wheeler Transform
• Similar in many ways to creation of Suffix Array
BANANA$Burrows-Wheeler Matrix
$BANANAA$BANANANA$BANANANA$BBANANA$NA$BANANANA$BA
Burrows-Wheeler Transform
• Similar in many ways to creation of Suffix Array
BANANA$
$BANANAA$BANANANA$BANANANA$BBANANA$NA$BANANANA$BA
Burrows-Wheeler Transform
• Similar in many ways to creation of Suffix Array
BANANA$
T(string) = ANNB$AA
Transformed String: Compressible and Reversible
$BANANAA$BANANANA$BANANANA$BBANANA$NA$BANANANA$BA
Burrows-Wheeler Transform
• Similar in many ways to creation of Suffix Array
BANANA$
T(string) = ANNB$AA
Suffix Array
$BANANAA$BANANANA$BANANANA$BBANANA$NA$BANANANA$BA
6531042
Burrows-Wheeler Transform
• Similar in many ways to creation of Suffix Array
BANANA$
TT(string) = ANNB$AA
FM-Index
$BANANAA$BANANANA$BANANANA$BBANANA$NA$BANANANA$BA
6531042
6, 5, 3, 1, 0, 4, 2
+
+Character Count Tables
Short Read Aligners
• BLAT: BLAST-Like Alignment Tool
• MAQ: First to take in to account quality scores
• Bowtie: One of the first to use BWT, ungappedalignment only
• BWA: One of the first to use BWT. First gapped BWT, incredibly fast and memory efficient
• Bowtie2: Allows indels
• SOAP, SOAP2: Also use BWT
• … and many more
Next-Gen Sequencing Experiments
• Whole Genome Sequencing
• Targeted Exome Sequencing
• RNA-Seq
• ChIP-Seq
• CLIP-Seq
Transcriptomics: RNA-Seq
• Sequence the actively transcribed genes in a cell line or tissue– Only about 20% of genes are transcribed in
particular cell types
• Two types:– Poly-A selection
– Total RNA + ribodepletion
• Many experimental questions can be addressed
RNA-Seq
• Important to take in to account biological variability. A sample of cells is a mixed population
– Replicates!
• Not suited for discovering polymorphisms due to higher error rates introduced by reverse transcription step (RNA -> cDNA)
• High false positive rates for fusion gene discovery, novel exons, when low expression levels
Overview/Objectives
• Genetic Variation– Types
• Identifying Genetic Variation– Methods
• Annotation of Genes and Variants– Methods
– Sources
• Gene/Variant Prioritization– Methods
Genetic Variation
• dbSNP (NCBI) build 142– Catalogs Single Nucleotide Variants (SNV)
– 365 Million Submitted
– 113 Million Validated
– 54 Million in Genes
– 36 Million With Frequency in Populations
• 50-80% of mutations involved in inherited disease caused by SNVs– May be an overestimate due to lack of knowledge
SNP vs SNV
• Technically a polymorphism is a variation that doesn’t cause disease and is common in a population
• What is common?
– Greater than 5% in a population a typical definition
– Definition for rare ranges from < 0.1% to < 1.0%
Frequency of Polymorphisms: Common vs Rare
• Mendelian disorders are caused by rare variation, < 1% frequency in the relevant population
• Leverage large projects aimed at assessing genetic diversity in populations around the world
Exome Sequencing Project
• Multi-Institutional
• Total possible patient pool of > 250,000 individuals, well phenotyped– Includes healthy individuals and diseased
• Currently 6700 exomes sequenced– 4420 European descent
– 2312 African American
• 1.2 million coding variations– Most extremely rare/unique
– Many population specific
Other Resources and Projects
• Exome Aggregation Consortium: 60,000 Exomes
• Personal Genome Project (Ongoing)
• 100,000 Genomes Project (UK, Ongoing)
• BGI (Announced, China): 1 Million Genomes
• Precision Medicine Initiative (US, Announced): 1 Million Genomes
Population Matters
• Most variations in protein-coding genes occurred fairly recently (last 20,000 years)
– Adaptation to agriculture and diet changes, pathogen exposure and urban living
Population Matters
• Most variations in protein-coding genes occurred fairly recently (last 20,000 years)– Adaptation to agriculture and diet changes, pathogen
exposure and urban living
• Monogenic diseases have different prevalence in different populations– Cystic fibrosis in European population
– Hereditary Hemochromatosis in Northern Europeans
– Tay-Sachs in Ashkenazi Jews
– Sickle-Cell Anemia in Sub-Saharan African populations
Finding All Needles
SNPs
ATCCTGATTCGGTGAACGTTATCGACGATCCGATCGACGGTGAACGTTATCGACGATCCGATCGAACTGTCAGCGGTGAACGTTATCGACGTTCCGATCGAACTGTCAGCG
TGAACGTTATCGACGTTCCGATCGAACTGTCAGCGGCTGAACGTTATCGACGTTCCGATCGAACTGTCAGCGGCTGAACGTTATCGACGTTCCGATCGAACTGTCAGCGGC
GTTATCGACGATCCGATCGAACTGTCAGCGGCAAGCTTTATCGACGATCCGATCGAACTGTCAGCGGCAAGCT
ATCCTGATTCGGTGAACGTTATCGACGATCCGATCGAACTGTCAGCGGCAAGCTGATCGATCGATCGATGCTAGTG
TTATCGACGATCCGATCGAACTGTCAGCGGCAAGCTTCGACGATCCGATCGAACTGTCAGCGGCAAGCTGAT
ATCCGATCGAACTGTCAGCGGCAAGCTGATCG CGATTCCGATCGAACTGTCAGCGGCAAGCTGATCG CGATC TCCGATCGAACTGTCAGCGGCAAGCTGATCGATCGA
GATCGAACTGTCAGCGGCAAGCTGATCG CGATCGA AACTGTCAGCGGCAAGCTGATCG CGATCGATGCTA
TGTCAGCGGCAAGCTGATCGATCGATCGATGCTAG
INDELs
ATCCTGATTCGGTGAACGTTATCGACGATCCGATCGA
TCAGCGGCAAGCTGATCGATCGATCGATGCTAGTG
reference genome
Finding All Needles
SNPs
ATCCTGATTCGGTGAACGTTATCGACGATCCGATCGACGGTGAACGTTATCGACGATCCGATCGAACTGTCAGCGGTGAACGTTATCGACGTTCCGATCGAACTGTCAGCG
TGAACGTTATCGACGTTCCGATCGAACTGTCAGCGGCTGAACGTTATCGACGTTCCGATCGAACTGTCAGCGGCTGAACGTTATCGACGTTCCGATCGAACTGTCAGCGGC
GTTATCGACGATCCGATCGAACTGTCAGCGGCAAGCTTTATCGACGATCCGATCGAACTGTCAGCGGCAAGCT
ATCCTGATTCGGTGAACGTTATCGACGATCCGATCGAACTGTCAGCGGCAAGCTGATCGATCGATCGATGCTAGTG
TTATCGACGATCCGATCGAACTGTCAGCGGCAAGCTTCGACGATCCGATCGAACTGTCAGCGGCAAGCTGAT
ATCCGATCGAACTGTCAGCGGCAAGCTGATCG CGATTCCGATCGAACTGTCAGCGGCAAGCTGATCG CGATC TCCGATCGAACTGTCAGCGGCAAGCTGATCGATCGA
GATCGAACTGTCAGCGGCAAGCTGATCG CGATCGA AACTGTCAGCGGCAAGCTGATCG CGATCGATGCTA
TGTCAGCGGCAAGCTGATCGATCGATCGATGCTAG
INDELs
ATCCTGATTCGGTGAACGTTATCGACGATCCGATCGA
TCAGCGGCAAGCTGATCGATCGATCGATGCTAGTG
reference genome
All regions with mismatches are potential variants
Genotype Calling: Determining the Type of Needle, The Absurdly Simple
Way (Stupid)
ATCCTGATTCGGTGAACGTTATCGACGATCCGATCGACGGTGAACGTTATCGACGATCCGATCGAACTGTCAGCGGTGAACGTTATCGACGTTCCGATCGAACTGTCAGCG
TGAACGTTATCGACGTTCCGATCGAACTGTCAGCGGCTGAACGTTATCGACGTTCCGATCGAACTGTCAGCGGCTGAACGTTATCGACGTTCCGATCGAACTGTCAGCGGC
GTTATCGACGATCCGATCGAACTGTCAGCGGCAAGCTTTATCGACGATCCGATCGAACTGTCAGCGGCAAGCT
ATCCTGATTCGGTGAACGTTATCGACGATCCGATCGAACTGTCAGCGGCAAGCTGATCGATCGATCGATGCTAGTG
TTATCGACGATCCGATCGAACTGTCAGCGGCAAGCTTCGACGATCCGATCGAACTGTCAGCGGCAAGCTGAT
TTCCGATCGAACTGTCAGCGGCAAGCTGATCGATCGA
ATCCTGATTCGGTGAACGTTATCGACGATCCGATCGA
reference genome
Read depth at base: 10 T: 4 A: 6
Genotype: Heterozygous A/T
Genotype Calling: The Absurdly Simple Way (Stupid)
• Doesn’t account for sequencing error
• Doesn’t account for sequencing bias
• Doesn’t count for bias in short-read mapping process
• Doesn’t account for mapping error
• Doesn’t consider any external source of information regarding populations or known genetic variations
Genotype Calling: The Absurdly Simple Way (Slightly less Stupid)
• Algorithm:
– Count all aligned bases that pass quality threshold (e.g. >Q20)
– If #reads with alternative base > lower bound (20%) and < upper bound (80%) call heterozygous alt
– Else if > upper bound call homozygous alternative
– Else call homozygous reference
• …But what about base qualities for more than keeping reads?
What’s Missing
• No estimate of the confidence (stats) of variant and genotype calls
• Doesn’t account robustly for known sources of error
What’s Missing
• No estimate of the confidence (stats) of variant and genotype calls
• Doesn’t account robustly for known sources of error
• Doesn’t make use of any sources of external information
What’s Missing
• No estimate of the confidence (stats) of variant and genotype calls
• Doesn’t account robustly for known sources of error
• Doesn’t make use of any sources of external information
• Doesn’t include base qualities
Improved Genotype Calling: Prior Probability
• Known Polymorphic Site?
– Allele Frequencies
• Global rate of polymorphisms
• Other samples
• Substitution Type
Substitution Type
• Transition: – Purine to Purine (A to G)
– Pyrimidine to Pyrimidine (C to T)
• Transversion– Purine to Pyrimidine
• Transition/Transversion ratio– Transitions 2x as common (Genome Wide)
– 4x when looking only at exons
– Random Error: 0.5
Prior Probability Example
Assume:Heterozygous SNP Rate of 0.001Homozygous SNP Rate of 0.0005Reference: GTransition/Transversion Ratio: 2
Prior Probability Example
A C G T
A 3.33x10-4 1.11x10-7 6.67x10-4 1.11x10-7
C 8.33x10-5 1.67x10-4 2.78x10-8
G 0.9985 1.67x10-4
T 8.33x10-5
Assume:Heterozygous SNP Rate of 0.001Homozygous SNP Rate of 0.0005Reference: GTransition/Transversion Ratio: 2
Improved Genotype Calling: Error Rates
Predicted Base
A C G T
Actual Base
A - 57.7 17.1 25.2
C 34.9 - 11.3 53.9
G 31.9 5.1 - 63.0
T 45.9 22.1 32.0 -
If a base was miscalled, what is it most likely to be called as instead?
Variant Calling
• SNP Calls infested with False Positives
– Machine artifacts
– Mis-mapped reads
– Mis-aligned indels
• 5 – 20% false positive rate
Decisions and Trade-Offs
• Option 1: Use stringent program options for calling variants and hard filtering early to produce only highly-confident call set.
Decisions and Trade-Offs
• Option 1: Use stringent program options for calling variants and hard filtering early to produce only highly-confident call set.
– Pro: Few false positives
– Con: Will miss real variants
Decisions and Trade-Offs
• Option 1: Use stringent program options for calling variants and hard filtering early to produce only highly-confident call set.
– Pro: Few false positives
– Con: Will miss real variants
• Option 2: Use less stringent (but reasonable) options and filtering. Produce high-confidence call set. Progressive filtering at later stage
Decisions and Trade-Offs
• Option 1: Use stringent program options for calling variants and hard filtering early to produce only highly-confident call set.– Pro: Few false positives
– Con: Will miss real variants
• Option 2: Use less stringent (but reasonable) options and filtering. Produce high-confidence call set. Progressive filtering at later stage– Pro: Won’t miss real variants
– Con: Many more false positives
Decisions and Trade-Offs
• Option 1: Use stringent program options for calling variants and hard filtering early to produce only highly-confident call set.– Pro: Few false positives
– Con: Will miss real variants
• Option 2: Use less stringent (but reasonable) options and filtering. Produce high-confidence call set. Progressive filtering at later stage– Con: False positives
– Pro: Won’t miss real variants
How Good Are My Calls?
• How many called SNPs?
– Human average of 1 heterozygous SNP / 1000 bases
• Fraction of variants already in dbSNP
– ~90%
• Transition/Transversion ratio
– Transitions 2x as common
• 3x when looking only at exons
Discovering Genetic Variants Causing Mendelian Disease
4 million genetic variants
2 million associated with protein-coding genes
10,000 possibly of disease
causing type
1500 <1% frequency in population
Single Causal Genetic Variant
If a problem cannot be solved, enlarge it.
--Dwight D. Eisenhower
Supreme Commander Allied Forces: Second World War34th President USA
Transcript Effects: Impact
Exon 1 Intron 1 Exon 2Reference
StartTAAStopmRNA coding for protein
Splice Sites
Transcript Effects: Impact
Exon 1 Intron 1 Exon 2Reference
Patient
StartTAAStopmRNA coding for protein
Exon 1 Intron 1 Exon 2
Splice Sites
Transcript Effects: Impact
Exon 1 Intron 1 Exon 2Reference
Patient
StartTAAStopmRNA coding for protein
Exon 1 Intron 1 Exon 2
Splice Sites
TACTyr
Transcript Effects: Impact
Exon 1 Intron 1 Exon 2Reference
Patient
StartTAAStopmRNA coding for protein
Exon 1 Intron 1 Exon 2
Splice Sites
TACTyrSplice Site Loss
Transcript Effects: Impact
Exon 1 Intron 1 Exon 2Reference
Patient
StartTAAStopmRNA coding for protein
Exon 1 Intron 1 Exon 2
Splice Sites
TACTyrSplice Site Loss
Missense
Transcript Effects: Impact
Exon 1 Intron 1 Exon 2Reference
Patient
StartTAAStopmRNA coding for protein
Exon 1 Intron 1 Exon 2
Splice Sites
TACTyrSplice Site Loss
Missense/Frameshift Stop Gain
Example: SIFT Algorithm
Input Query Sequence
Psi-BLAST
Homologs
Alignment
Multiple Sequence Alignment
Multiple Sequence Alignment
PSSM
NormalizeBy most
frequent AA
Score
Prediction Take-Away
The more conserved a site is the more likely any substitution is to be deleterious
However: Current methods have pretty poor performance, not suitable for clinical-level diagnosis
Classifying Genetic Variants
4 million variants
Intronic
Unknown Splice Site
Potential Disease Causing
Exonic
Amino Acid Changing
Known Genetic Disease Variant
Stop Loss / Stop Gain
Missense Mutation
Known Polymorphism in
Population
Silent Mutation Splice Site
Potential Disease Causing
Intergenic
Annotating Genes and Variants
• Is variant in a known protein-coding gene?
– What does the gene do?
– What molecular pathways?
– What protein-protein interactions?
– What tissues is it expressed in?
– When in development?
4 million genetic variants
2 million associated with protein-coding genes
10,000 possibly of disease
causing type
1500 <1% frequency in population
IGNITE Project: Local Controls
• IGNITE: Tasked with studying rare monogenic diseases identified in Atlantic Canada
• Atlantic Canada harbours several non-represented population groups and sub-groups…
IGNITE Project: Local Controls
• IGNITE: Tasked with studying rare monogenic diseases identified in Atlantic Canada
• Atlantic Canada harbours several non-represented population groups and sub-groups…
– Acadians
– Native American
– Non-Acadian/European Descent
Population Frequency
• Mendelian disorders are rare
• If variation is in database, is it associated with disease?
• Causal variation also needs to be rare
– Cutoff somewhere in the < 0.1 - < 1% range
– Should appear rarely or not at all in local controls
– Track with disease in family members under study
IGNITE Data Pipeline and Integration
Mapped Region(s)
Known Genes
Gene Definitions
Pathway and Interactions
Annotated Genomic Variants
FilterSort
Prioritize
Gene Annotations
Brain Calcification
• 84 genes in chromosome 5 region• No likely homozygous or compound heterozygous
variants within region shared between two patients
• 29 genes with at least one targeted region with little or no sequencing coverage
• Many only lacked coverage in 5’ and 3’ UTRs• Collaborators performed statistical tests for
possibly copy-number variations of targeted regions using exome sequencing data
Charcot-Marie-Tooth Cutis Laxa
• 143 genes in region• 13 known causative genes
– MPZ– PMP22– GDAP1– KIF1B– MFN2– SOX– EGR2– DNM2– RAB7– LITAF (SIMPLE)– GARS– YARS– LMNA
• 52 genes in region• 5 known causative genes
– ATP6V0A2– ELN– FBLN5– EFEMP2– SCYL1BP1– ALDH18A1
Pathway and Interaction Data
• 37 pathways– Clathrin-derived vesicle
budding
– Lysosome vesicle biogenesis
– Endocytosis
– Golgi-associated vesicle biogenesis
– Membrane trafficking
– Trans-Golgi network vesicle budding
• Primarily LMNA or DNM2
• 10 pathways– Phagosome
– Collecting duct acid secretion
– Lysosome
– Protein digestion and absorption
– Metabolic pathways
– Oxidative phosphorylation
– Arginine and prolinemetabolism
• Primarily ATP6V0A2
Simple Prioritization
Pathways and Protein-Protein Interactions of Known Genes
Pathways and Protein-Protein Interactions of Variant Genes
Results: Charcot-Marie-Tooth
• 8 Genes PrioritizedGene Interactions PathwayLRSAM1 Multiple EndocytosisDNM1 DNM2 -FNBP1 DNM2 -TOR1A MNA -STXBP1 Multiple FiveSH3GLB2 - EndocytosisPIP5KL1 - EndocytosisFAM125B - Endocytosis
• For more information– Guernsey et al (2010) PLoS Genetics. 6(8): e1001081
Results: Cutis Laxa• 10 genes prioritizedGene Interactions PathwayHEXDC Multiple PhagosomeHG5 - PhagosomeHG5 Multiple Lysosome, Protein digestionSIRT7 Multiple Metabolic PathwaysFASN - Metabolic PathwaysDCXR - Metabolic PathwaysPYCR1 - Metabolic Pathways,
Arginine/ProlinePCYT2 - Metabolic PathwaysARHGDIA - Oxidative Phosphorylation
• For more information – Guernsey et al (2009) Am J Hum Genet. 85(1): 120-9