A rare variant in MYH6 confers high risk of sick sinus syndrome. Hilma Hólm ESC Congress 2011 Paris, France

Transcription

1 A rare variant in MYH6 confers high risk of sick sinus syndrome Hilma Hólm ESC Congress 2011 Paris, France

2 Disclosures I am an employee of decode genetics, Reykjavik, Iceland.

3 Sick sinus syndrome SSS is a common clinical disorder, primarily of the elderly population It is characterized by inappropriate sinus bradycardia (slow heart rate), sinus arrest and/or chronotropic incompetence (failure to increase heart rate with exercise) as well as increased susceptibility to atrial tachyarrythmias SSS is the most common indication for pacemaker (PM) implantation Symptoms of SSS are often vague and/or intermittent

4 Previously implicated genes in SSS Candidate gene studies have previously identified gene mutations in sporadic cases and kindreds with familial sick sinus syndrome (both with and without other concomitant cardiac conditions) Implicated genes have primarily been ion channel or ion channel-associated genes including SCN5A, HCN4, Cx40 and ANK2

5 Genome-wide association study on SSS Our objective was to conduct an unbiased search for sequence variants that predispose to SSS R721W We performed a genome-wide association study of Icelanders with SSS including 792 cases with SSS and 37,592 controls, testing 7.2 million SNPs either directly genotyped with the Illumina HumanHap300/CNV370 chips or imputed from one or more of four sources; the HapMap CEU sample, the 1000 Genomes data and Icelandic samples genotyped with the Illumina 1M and/or the Omni chips

6 SSS GWAS: Initial results Source SNP P value OR MAF Directly genotyped rs Imputed from HapMap2 rs Imputed from the 1000 Genomes project Imputed from the Human1M-Duo chip rs Imputed from the HumanOmni1-Quad chip rs Imputed from the HumanOmni1-Quad chip rs R721W The association analysis yielded association with several correlated SNPs in and near MYH6-MYH7 on chromosome 14 (never before associated with SSS)

7 Refinement of the SSS signal For refinement of the signal on chr 14q11, we selected seven chip typed SSS cases for whole-genome sequencing, four that carry the rs [t] variant (the minor and risk allele) In our analysis we used whole-genome sequencing data from additional 80 individuals, not diagnosed with SSS, and including one additional carrier of the rs [t] variant Based on these sequencing data, a total of ~11 million SNPs were called and imputed into chip typed cases and controls and tested for association with SSS

8 Whole-genome sequencing results All four SSS cases that carried the rs [t] variant had the same R721W missense mutation in MYH6 (freq = 0.38%) No one else had the R721W mutation, including neither the noncarrier SSS cases nor the carrier control No significant association with SSS was found outside the 14q11 region Carrier = carrier of the rs minor allele T

9 R721W associates strongly with SSS To increase imputation accuracy, we genotyped additional 874 chip typed Icelanders with a R721W Centaurus assay and combined with the 87 whole-genome R721W sequenced samples into a set of 952 individuals (five individuals overlapped and nine could not be phased accurately in the region around MYH6), of which 73 are carriers of the R721W mutation, creating a new reference set for imputation. Based on this imputation set, the association is stronger than when based on the initial imputation set. The R721W missense mutation in MYH6 (estimated allelic frequency in Iceland R721W = 0.38%) associates with SSS with an OR of (95% CI: 8.08, 19.44) and a corresponding P value of

10 Replication in an independent Icelandic SSS sample A second set of 469 Icelandic SSS cases and 1,185 controls who were not chip R721W genotyped and therefore unavailable for the haplotype based imputation, were genotyped for the R721W mutation with the R721W Centaurus single SNP assay. Among the SSS cases 20 heterozygous carriers of R721W were identified (allelic frequency of 2.1%) while only five heterozygous carriers were observed among the controls (allelic frequency of 0.21%). This replicates the original association with SSS based on imputations (OR = 12.95, P = ). R721W

11 Genome-wide association study Refinement of SSS signal on chr 14 Association analysis testing 7.2 million SNPs in 792 chip typed SSS cases and 37,592 chip typed controls. Selection of seven SSS cases, four that carry rs [t], into our whole-genome sequencing project. WGS data from 87 individuals imputed in all cases and controls. Association analysis testing ~11 million SNPs. Association with rs [t] on chr 14q11, MAF OR = 3.49 P = Strong association with MYH6 R721W missense mutation No significant association outside the 14q11 region Improving imputation accuracy R721W genotyped in 874 chip typed Icelanders (enriched for carriers of rs [t]) and imputed into all chip typed cases and controls. Association analysis. OR =12.53 P = Independent replication R721W genotyped in previously un-typed subjects, 469 Icelandic SSS cases and 1,185 controls. OR = P =

12 Association with ECG parameters We have previously published a large GWAS on ECG measures, utilizing a large ECG database originating from Landspitali University Hospital in this study we showed that a common SNP in MYH6 (rs365990) associates with both heart rate (effect = 0.9 beats per minute and PR interval duration (effect = -1.1 milliseconds) We now tested the R721W missense mutation for association with ECG measures in ~12,000 Icelanders with genome-wide data (after excluding those with SSS or a PM) We found that R721W occurs on the minor allele of rs (all subjects with the R721W mutation have the rs minor allele) and associates significantly with heart rate (effect = 4.5 bpm, P = ) and PR interval (effect = 6.3 msec, P = 0.012) after exclusion of all cases with SSS and PM

13 Association with heart rate: Common vs rare variants

14 MYH6 Cardiac muscle myosin, along with actin, is one of the major components of the sarcomere, the building block of the contractile system of cardiac muscle MYH6 encodes the alpha-cardiac myosin heavy chain (α-myhc), one of two sarcomeric MyHC isoforms that are expressed in the mammalian myocardium, and is primarily expressed in the atria MYH7 encodes β-myhc and mutations in this gene are a well-known cause of hypertrophic cardiomyopathy in man Mutations in MYH6 were recently linked to both cardiomyopathy (hypertrophic and dilated) and a variety of congenital heart defects Neither MYH6 nor MYH7 have been specifically linked to conduction defects in man before However, studies in mice have indicated that micro RNA 208a encoded by an intron of MYH6 is both necessary for proper cardiac conduction and that both lack-of- and gain-offunction of mrna208a can induce arrhythmias This is the first time MYH6 is linked to a cardiac conduction disorder in man

15 Penetrance of the SSS mutation

16 Follow-up in other populations The R721W mutation itself is neither present in the available 1000 Genomes project data nor in the HapMap samples We also directly tested for the presence of R721W in 184 Danish, 94 Dutch and 1498 US controls as well as 135 US SSS cases without observing a single carrier of R721W. However, pooled sequencing of SSS cases and controls from both Duke and Vanderbilt yielded several missense variants in MYH6 that were only observed in cases. These have been confirmed with Sanger sequencing and are now subject to further follow up in additional cases and controls.

17 SSS is a common disease with often vague and intermittent symptoms and can be difficult to diagnose The R721W variant in MYH6 associates with SSS with an OR of and the lifetime risk of carriers of developing SSS is at least 50%

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