development of a new method to prioritise gene analysis in familial hypertrophic cardiomyopathy
DESCRIPTION
Development of a New Method to Prioritise Gene Analysis in Familial Hypertrophic Cardiomyopathy. Jayne Duncan West of Scotland Regional Genetics Service, Glasgow. Familial Hypertrophic Cardiomyopathy (FHC). Autosomal dominant disorder showing variable penetrance and age of onset. - PowerPoint PPT PresentationTRANSCRIPT
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Development of a New Method to Prioritise Gene Analysis in
Familial Hypertrophic Cardiomyopathy
Jayne Duncan
West of Scotland Regional Genetics Service, Glasgow
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Familial Hypertrophic Cardiomyopathy (FHC)
• Autosomal dominant disorder showing variable penetrance and age of onset.
• Affects approximately 1/500 adults and is the most common cause of sudden death in young healthy individuals.
• So far mutations in over 20 genes have been associated with FHC
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Primary Clinical Features of FHC
• Left ventricular hypertrophy, “a thickening of the tissue due to increased size of the constituent cells”.
• Myocyte/myofibrillar disarray caused by the abnormal shapes, intracellular connections and arrangement of the hypertrophic myocytes and fibrosis.
1 http://www.maxshouse.com2 Arad et al 2002 Hum Mol Genet. 11. (20) 2499-2506
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Genotype Phenotype Correlation
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The Heterogeneous Nature of FHC
• HCM is caused by dominant mutations in the sarcomeric genes.
• de novo mutations occur rarely and account for approximately 10% of cases.
• Mutations in the sarcomeric genes account for ~55% of cases of HCM.
• Syndromes such as the Glycogen storage disorders and Friedreich ataxia can mimic HCM.
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Glasgow Linkage Exclusion Analysis Method (GLEAM)
• Glasgow Linkage Exclusion Analysis Method (GLEAM)
• Novel method to prioritise gene analysis in heterogeneous disorders
• A gene is excluded from analysis when affected relatives are oppositely homozygous for SNPs in and around the gene of interest
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GLEAM
• A and B represent alleles at a susceptibility locus for a dominantly inherited disorder affecting individuals II:2, II:3, III:1 and III4.
• Since III:1 has no allele in common with II:3 or III:4 it effectively rules out this locus as being responsible for the disease in this family.
I:1 I:2
II:2II:1 II:3 II:4
III:1 III:2 III:3 III:4
BB AB AA AB
BB AB AB AA
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Genes analysed in the FHC Project
Gene Name Chromosome No Exons No SNPs
TTN 2 363 212
MYH7 14 38 76
MYH6 14 37 77
MYBPC3 11 35 147
RAF1 3 16 163
PRKAG2 7 16 146
TPM1 15 16 132
TNNT2 1 15 116
MYLK2 20 12 94
TNNI3 19 8 92
MYL3 3 7 89
MYL2 12 7 94
CAV3 3 2 98
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SNP Analysis Platform
• 96 fibre optic bundles on each plate• Each fibre contains a bead that corresponds to
each SNP• Image taken from www.Illumina.com
Sentrix Array Matrix
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Results- Raw Data
Raw data for one patient sample
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Results- Raw Data
Clustered patient SNP data for a single SNP locus
AA BBAB
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Results- Genotype Comparisons
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Results
Relationship Number of pairs Average numberof genes excluded
Sibs 49 3
Aunt/NieceNephew
22 5
First Cousins 10 7
First Cousins once removed
5 8
Second Cousins 9 7
Grandparent/Grandchild
1 2
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ResultsGene Number of times
gene excluded Percentagenumber of timesgene excluded
TTN 34/96 35%
MYH6 and MYH7 33/96 34%
MYBPC3 28/96 29%
RAF1 23/96 24%
PRKAG2 47/96 49%
TPM1 29/96 30%
TNNT2 39/96 41%
MYLK2 40/96 42%
TNNI3 34/96 35%
MYL3 33/96 34%
MYL2 26/96 27%
CAV3 40/96 42%
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Interesting Case
I:1 I:2
II:1 II:3II:2
III:2III:1
IV:1 IV:2 IV:3
II:4
III:4III:3 III:5 III:7III:6
IV:4 IV:5 IV:6
H15.1 H15.4 H15.7 H15.14 H15.15 H15.16 H15.12
TNNI3/ TNNI3/ MYBPC3 TNNI3 TNNI3 TNNI3 TNNI3 MYBPC3 MYBPC3
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Interesting Case
• Familial mutation in TNNI3 was not excluded in all affected family members.
• Comparisons between H15.1, H15.4 and H15.7 did not exclude MYBPC3.
• MYBPC3 was excluded when H15.1, H15.4 and H15.7 were compared against other family members who did not have this mutation.
• Testing for the TNNI3 mutation in H15.7 would have been negative and suggested a second mutation prompting further analysis.
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Conclusions
• For all the pedigrees with one known mutation, this gene was not excluded in any of the analyses performed.
• More genes tend to be excluded when more distantly related individuals such as first cousins or aunt/niece, nephew pairs are considered, rather than more closely related sibs
• GLEAM can be used to determine the order in which genes are sequenced in heterogeneous disorders
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Acknowledgements
• Scottish Health Innovations Ltd
• Dr Wai Lee & Dr Stewart Lang, British Heart Foundation, Glasgow Cardiovascular Research Centre, University of Glasgow.
Dr Petros Syrris, Department of Medicine, University College London