Molecular mechanism of a new cardiac syndrome associated with a regulatory element deletion of chromosome 4q25

Introduction

We identified a large family of 53 members of whom 22 present a new cardiac syndrome characterized by electrical disorders and developmental defects following an autosomal dominant model. Among the affected family members 6 are implanted with a pacemaker, 2 experienced syncope and one a sudden death at 43yo. Linkage analysis points, with high confidence, to the chromosome 4q25 region. This region is associated with the Ankyrin syndrome (mutation in ANK2) sharing partly the electrical defects observed in the affected family members. No mutation was found in the coding region of the 4q25 region as well as in the coding and non-coding part of the ANK2.

Objective

Our aims are first to identity the responsible mutation present in this family and understand the molecular mechanisms leading to this new syndrome.

Method

Whole genome sequencing (WGS) has been employed to identify genetic variants responsible for this syndrome. ChIP-seq and ATAC-seq were used for functional annotation and genome editing (CRISPR-Cas9) to generate iPS cellular models.

Results

By WGS we uncovered a deleted region of 15kb in a gene desert area on 4q25, segregating in all affected relatives. Five other families (3 French and 2 Japanese) presenting the same phenotype show overlapping deletions. We generated human cardiac epigenetic data and identified among the 15kb deleted region a unique active enhancer region within the presence of a transcript factor CTCF binding site. Isogenic cell lines where the 15kb and the CTCF binding have been deleted are under investigation.

Conclusion

We identified a new cardiac syndrome and for the first time a mutation located within a gene desert area leading to severe and complex cardiac disorders. We demonstrated the presence of a likely gene regulatory element. Experiments are ongoing to characterize the molecular mechanisms and consequence of the deletion on gene expression.

Funding Acknowledgement

Type of funding source: Public Institution(s). Main funding source(s): Pays de la loire - Etoiles montantes

P756 Paradoxycal restricted motion in diastole associated to mitral valve prolapse/dystrophy: a frequent finding

Funding Acknowledgements

PHRCI mitral 2012

Background

Filamin-A mitral valve prolapse/dystrophy (FLNA-MVP) phenotype associates moderate MVP and a paradoxical restricted motion in diastole.

Purpose

We aimed to assess the association of MVP with restricted motion in diastole in MVP patients (restricted MVP).

Methods

We prospectively enrolled 433 MVP probands (57 ± 16 years). Patients underwent a clinical examination and a comprehensive echocardiographic analysis of mitral valve apparatus.

Results Among the 433 probands, 27 (6.2%, 95% CI 3.9-8.5) had both a MVP and a doming aspect in diastole. Patients with restricted MVP exhibited shorter posterior chordae tendinaes (24.8 ± 6.3 vs 27.2 ± 5.9 mm, P = 0.037), and a shorter distance between papillary muscle (PM) tips and mitral annulus (anterior PM: P = 0.0001; posterior PM: P = 0.009). Anterior mitral valve leaflet was lengthened (15.5 ± 2.4 vs 14.3 ± 2.6 mm/m², P = 0.018), but leaflet thickness, leaflet prolapse, and mitral valve annulus did not differ between the 2 groups. Bicuspid aortic valve was more frequent in patients with restricted phenotype (14.8 vs 2.9%, P < 0.05). Familial recurrence of restricted MVP was identified even in the absence of Filamin-A mutation.

Conclusion

Restricted MVP is a quite frequent finding in MVP patients and is associated with PM tips location closer to mitral annulus. Restricted MVP can be regarded as a third type of MVP beside myxomatous Barlow disease and fibro-elastic deficiency MVP.

P2864A novel mechanism of sinus node dysfunction: intergenic deletion between PITX2 and ANK2 disrupts chromatin structure in pacemaker cell differentiation

Background

Genetics of sinus node dysfunction (SND) remains poorly understood with few genes identified (HCN4, SCN5A, GJA5, KCNQ1, MYH6 and ANK2) and further genetic heterogeneity.

Purpose

We report two families with SND segregating with an intergenic deletion associated with long-range cis-regulatory elements (CREs) of PITX2.

Methods

We applied 30x whole genome sequencing (WGS) to two French families in which exome sequencing did not allow to detect the causing genes of SND and analyzed them bioinformatically.

Results

We first applied WGS to a 4-generation family presenting 16 patients with SND, atrial fibrillation and/or repolarization abnormalities and identified a 15-Kb deletion within a 16.5-cM linkage interval (Zmax = 5.9, θ = 0) on chromosome 4q25. We also applied WGS on a second family presenting 5 patients with SND and identified a 91-Kb deletion overlapping the initial deletion. This intergenic deletion, which was located between PITX2 and ANK2 and contained a binding motif of CCCTC-binding factor (CTCF), was segregating in all patients and was not found in 855 French control genomes. CTCF functions as a genome organizer mediating genomic interactions between genes and CREs. To clarify a possible regulatory function of the 1.5-Mb intergenic region containing the deletion, we interrogated 3 epigenetic databases. High-throughput chromosome conformation capture (Hi-C) (1) revealed that this intergenic region was placed in a topologically associating domain (TAD) containing PITX2. Chromatin interaction analysis by paired-end tag (ChIA-PET) of CTCF (2) suggested several possible functional chromatin loops in the TAD. Of them, a CTCF-mediated chromatin loop corresponding to a 300-Kb genomic region was clarified as a possible CRE using histone modification data from Roadmap. The region ranging between the intra-deletion CTCF motif and another distal motif was repressed in H3K27me3 profiles of fetal heart, while the region was activated in H3K27ac profiles of H1 ESC-derived mesendoderm.

Conclusion

This CRE may regulate expression of PITX2 and/or ANK2 in pacemaker cell differentiation. Ongoing experiments on patient's iPSC and transgenic mouse will further characterize the disease mechanism.

P6490Paradoxycal restricted motion in diastole is a frequent finding in mitral valve prolapse/dystrophy patients

Background

Filamin-A mitral valve prolapse/dystrophy (FLNA-MVP) phenotype associates MVP and a paradoxical restricted motion in diastole.

Purpose

We aim to assess the association of mitral valve prolapse to restricted motion in diastole in MVP patients (restricted MVP).

Methods

We prospectively enrolled 475 MVP probands (64±13 years) and controls relatives. Patients underwent a clinical examination and a comprehensive echocardiographic analysis of mitral valve apparatus.

Results

Among 475 consecutive probands, 48 (10.1%, 95% CI 7.7–13.3) had both a MVP and a doming aspect in diastole. Patients with restricted MVP exhibited shorted chordae tendinaes, and a shorter distance between papillary muscle tip and mitral annulus. Compared with controls, mitral valve leaflets were lenghtened, thickened and mitral valve annulus was enlarged. The prevalence of polyvalvular disease and bicuspid aortic valve was not increased in restricted MVP patients compared with conventional MVP. Familial form of restricted MVP was identified even in the absence of Filamin-A mutation.

Conclusion

Restricted MVP is a quite frequent finding in MVP patients and is associated with unique features of the MV apparatus. Restricted MVP can be regarded as a third type of MVP beside myxomatous Barlow disease and fibro-elastic deficiency MVP.

Acknowledgement/Funding

PHRC I Mitral, Fédération Française de Cardiologie, Fondation Coeur et recherche

[Genetic aspects of valvulopathies]

Valvular dystrophies due to myxoid degeneration are common and potentially serious cardiac pathologies. They constitute a heterogeneous group of which the most usual is idiopathic mitral valvular prolapse (Barlow's disease). The majority of mitral valvular prolapses are sporadic, but there are several familial forms. Transmission is usually autosomal dominant with incomplete penetrance and variable expression. The first chromosomal location to be identified was on the 16p11-13 chromosome. Since then, two other loci have been identified on the 11p15.4 and 13q31-32 chromosomes. Our team has recently identified the first gene responsible for myxoid valvulopathy linked to the X chromosome, from a large family of 318 members. This is the gene that codes for filamin A, which is a cytoskeleton protein. The frequency of mutations in this gene is still unknown, but out of 7 families in which transmission was compatible with X-linked transmission, mutations were discovered in 4 of the families. Thanks to a genetic epidemiological approach, we have also demonstrated that there are familial forms of aortic stenosis, which are probably common. Identification of the genes implicated in these common forms of valvular pathology is important, as it will allow a better understanding of the pathophysiology of these valvular disorders and could lead to better therapeutic management in the future.