Development of a New Method to Prioritise Gene Analysis in Familial Hypertrophic Cardiomyopathy

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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.com
• 2 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 II2, II3, III1 and III4.
  
• Since III1 has no allele in common with II3 or
  III4 it effectively rules out this locus as
  being responsible for the disease in this family.

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Genes analysed in the FHC Project
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SNP Analysis Platform
Sentrix Array Matrix

• 96 fibre optic bundles on each plate
• Each fibre contains a bead that corresponds to
  each SNP
• Image taken from www.Illumina.com

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Results- Raw Data
Raw data for one patient sample
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Results- Raw Data
AB
AA
BB

• Clustered patient SNP data for a single SNP
  locus

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Results- Genotype Comparisons
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Results
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Results
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Interesting Case
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