FLNC Gene Splice Mutations Cause Dilated Cardiomyopathy

Abstract

Objective To identify novel dilated cardiomyopathy (DCM) causing genes, and to elucidate the pathological mechanism leading to DCM by utilizing zebrafish as a model organism. Background DCM, a major cause of heart failure, is frequently familial and caused by a genetic defect. However, only 50% of DCM cases can be attributed to a known DCM gene variant, motivating the ongoing search for novel disease genes. Methods We performed whole exome sequencing (WES) in two multigenerational Italian families and one US family with arrhythmogenic DCM without skeletal muscle defects, in whom prior genetic testing had been unrevealing. Pathogenic variants were sought by a combination of bioinformatic filtering and cosegregation testing among affected individuals within the families. We performed function assays and generated a zebrafish morpholino knockdown model. Results A novel filamin C gene splicing variant (FLNC c.7251+1 G>A) was identified by WES in all affected family members in the two Italian families. A separate novel splicing mutation (FLNC c.5669-1delG) was identified in the US family. Western blot analysis of cardiac heart tissue from an affected individual showed decreased FLNC protein, supporting a haploinsufficiency model of pathogenesis. To further analyze this model, a morpholino knockdown of the ortholog filamin Cb in zebrafish was created which resulted in abnormal cardiac function and ultrastructure. Conclusions Using WES, we identified two novel FLNC splicing variants as the likely cause of DCM in three families. We provided protein expression and in vivo zebrafish data supporting haploinsufficiency as the pathogenic mechanism leading to DCM.

De novo mutations in FLNC leading to early-onset restrictive cardiomyopathy and congenital myopathy

“…Interestingly, both in vitro and in vivo models used revealed some inconsistency in aggregate formation. While we were not able to detect any alteration of intracellular filamin C network or protein aggregates formation in C2C12 cells with either p.A1183L or p.A1186V mutations, overexpression of mutant FNLC in zebrafish revealed the presence of FNLC aggregates consistent with previously reported zebrafish models for FNLC ‐myopathies (Ruparelia et al., ; Begay et al., ). This, possibly, can be explained by the absence of a proper Z‐line architecture in C2C12 cells and, thus, lack of a proper binding partners for FLNC triggering aggregate formation in an area of Z‐line discs.…”

“…One such gene is FLNC , known for a long time exclusively in association with distal and myofibrillar myopathies (Kley et al., ), and only more recently described in connection to cardiac phenotypes (Kley et al., ; Valdes‐Mas et al., ; Vorgerd et al., ). After the first description of FLNC mutation in a familial case of HCM in 2014, the number of reports documenting its role in the development of cardiac disorders has rapidly grown, making FLNC one of the most common genes associated with cardiomyopathies causing about 10% of HCM and up to 5% of DCM (Begay et al., ; Brodehl et al., ; Dal Ferro et al., ; Gomez et al., ; Janin et al., ; Ortiz‐Genga et al., ; Reinstein et al., ; Tucker et al., ; Valdes‐Mas et al., ). Similar to titin , FLNC is linked to all types of cardiomyopathies, including arrhythmogenic cardiomyopathy.…”

“…Notably, RCM myocardial dysfunction, as well as other types of cardiomyopathies, can manifest concomitant with skeletal muscle system pathology, highlighting the involvement of genes expressed both in cardiac and skeletal muscle (Janin et al., ; Konersman et al., ; Kostareva, Sejersen, & Sjoberg, ). One such gene recently associated with several types of cardiomyopathies is FLNC (MIM# 102565) (Begay et al., ; Brodehl et al., ; Gomez et al., ; Ortiz‐Genga et al., ; Reinstein et al., ; Valdes‐Mas et al., ). FLNC encodes filamin C, an actin cross‐linking protein abundant both in cardiomyocytes and skeletal muscle cells.…”

Novel pathogenic variants in filamin C identified in pediatric restrictive cardiomyopathy

“…FLNC variants are a recently recognized cause of phenotypically distinct cardiomyopathies including HCM, DCM, and RCM (Begay et al., ; Brodehl et al., ; Valdés‐Mas et al., ). FLNC‐ related cardiomyopathies present a challenge in extrapolating genotype‐phenotype correlations based on variant position (Table ).…”

Dilated Cardiomyopathy

“…More recently FLNC mutations, in the gene encoding filamin C, have been described in DCM 125–127 . Filamin C interacts with the dystrophin complex, and deletion of Flnc from the mouse leads to skeletal myopathy 128, 129 .…”