D117N in Cypher/ZASP may not be a causative mutation for dilated cardiomyopathy and ventricular arrhythmias

Left Ventricular Non-Compaction in Children: Aetiology and Diagnostic Criteria

Left ventricular non-compaction (LVNC) is a heterogeneous myocardial disorder characterized by prominent trabeculae protruding into the left ventricular lumen and deep intertrabecular recesses. LVNC can manifest in isolation or alongside other heart muscle diseases. Its occurrence among children is rising due to advancements in imaging techniques. The origins of LVNC are diverse, involving both genetic and acquired forms. The clinical manifestation varies greatly, with some cases presenting no symptoms, while others typically manifesting with heart failure, systemic embolism, and arrhythmias. Diagnosis mainly relies on assessing heart structure using imaging tools like echocardiography and cardiac magnetic resonance. However, the absence of a universally agreed-upon standard and limitations in diagnostic criteria have led to ongoing debates in the scientific community regarding the most reliable methods. Further research is crucial to enhance the diagnosis of LVNC, particularly in early life stages.

Cardiac Filaminopathies: Illuminating the Divergent Role of Filamin C Mutations in Human Cardiomyopathy

Over the past decades, there has been tremendous progress in understanding genetic alterations that can result in different phenotypes of human cardiomyopathies. More than a thousand mutations in various genes have been identified, indicating that distinct genetic alterations, or combinations of genetic alterations, can cause either hypertrophic (HCM), dilated (DCM), restrictive (RCM), or arrhythmogenic cardiomyopathies (ARVC). Translation of these results from “bench to bedside” can potentially group affected patients according to their molecular etiology and identify subclinical individuals at high risk for developing cardiomyopathy or patients with overt phenotypes at high risk for cardiac deterioration or sudden cardiac death. These advances provide not only mechanistic insights into the earliest manifestations of cardiomyopathy, but such efforts also hold the promise that mutation-specific pathophysiology might result in novel “personalized” therapeutic possibilities. Recently, the FLNC gene encoding the sarcomeric protein filamin C has gained special interest since FLNC mutations were found in several distinct and possibly overlapping cardiomyopathy phenotypes. Specifically, mutations in FLNC were initially only linked to myofibrillar myopathy (MFM), but are now increasingly found in various forms of human cardiomyopathy. FLNC thereby represents another example for the complex genetic and phenotypic continuum of these diseases.

Impact of LDB3 gene polymorphisms on clinical presentation and implantable cardioverter defibrillator (ICD) implantation in Chinese patients with idiopathic dilated cardiomyopathy

OBJECTIVE

Mutations in LIM domain binding 3 (LDB3) gene cause idiopathic dilated cardiomyopathy (IDCM), a structural heart disease with a complicated genetic background. However, the association of polymorphisms in the LDB3 gene with susceptibility to IDCM in Chinese populations remains unexplored as dose the impact on clinical presentation.

METHODS

We sequenced all exons and the adjacent part of introns of the LDB3 gene in 159 Chinese Han IDCM patients and 247 healthy controls. Then we detected the distribution of polymorphisms in the LDB3 gene in all participants and assessed their associations with risk of IDCM. Additionally, we conducted a stratified genotype-phenotype correlation analysis.

RESULTS

The A allele of rs4468255 was significantly associated with IDCM (P<0.01). The rs4468255, rs11812601, rs56165849, and rs3740346 were also associated with diastolic blood pressure (DBP) and left ventricular ejection fraction (LVEF) (P<0.05). Notably, a higher frequency of rs4468255 polymorphism was observed in implantable cardioverter defibrillator (ICD) recipients under a recessive model (P<0.01), whereas the significant association disappeared after adjusting for potential confounders. However, in the dominant model, notable correlations could only be observed after adjusting for multi parameters.

CONCLUSIONS

The rs4468255 was significantly correlated with IDCM of Chinese Han population. A allele of rs4468255 is higher in IDCM patients with ICD implantation, suggesting the influence of genetic background in the generation of this response. In addition, rs11812601, rs56165849, and rs3740346 in LDB3 show association with brain natriuretic peptide, DBP, and LVEF levels in patients with IDCM but did not show any association with IDCM susceptibility.

Cardiomyopathy due to PRDM16 mutation: First description of a fetal presentation, with possible modifier genes

PRDM16 (positive regulatory domain 16) is localized in the critical region for cardiomyopathy in patients with deletions of chromosome 1p36, as defined by Gajecka et al., American Journal of Medical Genetics, 2010, 152A, 3074-3083, and encodes a zinc finger transcription factor. We present the first fetal case of left ventricular non-compaction (LVNC) with a PRDM16 variant. The third-trimester obstetric ultrasound revealed a hydropic fetus with hydramnios and expanded hypokinetic heart. After termination of pregnancy, foetopathology showed a eutrophic fetus with isolated cardiomegaly. Endocardial fibroelastosis was associated with non-compaction of the myocardium of the left ventricle. Exome sequencing (ES) identified a de novo unreported p.(Gln353*) heterozygous nonsense variant in PRDM16. ES also identified two rare variants of unknown significance, according to the American College of Medical Genetics and Genomics guidelines, in the titin gene (TTN): a de novo missense p.(Lys14773Asn) variant and a c.33043+5A>G variant inherited from the mother. Along with the PRDM16 de novo probably pathogenic variant, TTN VOUS variants could possibly contribute to the severity and early onset of the cardiac phenotype. Because of the genetic heterogeneity of cardiomyopathies, large panels or even ES could be considered as the main approaches for the molecular diagnosis, particularly in fetal presentations, where multiple hits seem to be common.

Downregulation of Cypher induces apoptosis in cardiomyocytes via Akt/p38 MAPK signaling pathway

Background: Dilated cardiomyopathy (DCM) is considered as the most common form of non-ischemic cardiomyopathy with a high mortality worldwide. Cytoskeleton protein Cypher plays an important role in maintaining cardiac function. Genetic studies in human and animal models revealed that Cypher is involved in the development of DCM. However, the underlying molecular mechanism is not fully understood. Accumulating evidences suggest that apoptosis in myocytes may contribute to DCM. Thus, the purpose of this study is to define whether lack of Cypher in cardiomyocytes can elevate apoptosis signaling and lead to DCM eventually. Methods and Results: Cypher-siRNA sufficiently inhibited Cypher expression in cardiomyocytes. TUNEL-positive cardiomyocytes were increased in both Cypher knockdown neonatal rat cardiomyocytes and Cypher knockout mice hearts, which were rare in the control group. Flow cytometry further confirmed that downregulation of Cypher significantly increased myocytes apoptosis in vitro. Cell counting kit-8 assay revealed that Cypher knockdown in H9c2 cells significantly reduced cell viability. Cypher knockdown was found to increase cleaved caspase-3 expression and suppress p21, ratio of bcl-2 to Bax. Cypher-deficiency induced apoptosis was linked to downregulation of Akt activation and elevated p-p38 MAPK accumulation. Pharmacological activation of Akt with SC79 attenuated apoptosis with enhanced phosphorylation of Akt and reduced p-p38 MAPK and Bax expression. Conclusions: Downregulation of Cypher participates in the promotion of cardiomyocytes apoptosis through inhibiting Akt dependent pathway and enhancing p38 MAPK phosphorylation. These findings may provide a new potential therapeutic strategy for the treatment of DCM.

Novel polymorphisms in PDLIM3 and PDLIM5 gene encoding Z-line proteins increase risk of idiopathic dilated cardiomyopathy

Idiopathic dilated cardiomyopathy (IDCM), characterized by ventricular dilation and impaired systolic function, is a primary cardiomyopathy resulting in heart failure. During heart contraction, the Z‐line is responsible for transmitting force between sarcomeres and is also a hot spot for muscle cell signalling. Mutations in Z‐line proteins have been linked to cardiomyopathies in both humans and mice. Actinin‐associated LIM protein (ALP) and enigma homolog protein (ENH), encoded by PDLIM3 and PDLIM5, are components of the muscle cytoskeleton and localize to the Z‐line. A PDLIM3 or PDLIM5 deficiency in mice leads to dilated cardiomyopathy. Since PDLIM3 and PDLIM5 are candidate IDCM susceptibility genes, the current study aims to investigate whether polymorphisms within PDLIM3 and PDLIM5 could be correlated with IDCM. We designed a case‐control study, and exons of the PDLIM3 and PDLIM5 were amplified by polymerase chain reactions in 111 IDCM patients and 137 healthy controls. We found that five synonymous polymorphisms had statistical distribution differences between IDCM patients and controls, including rs4861669, rs4862543, c.731 + 131 T > G, c.1789‐3 C > T and rs7690296, according to genotype and allele distribution. Haplotype G‐C‐C‐C and A‐T‐C‐T (rs2306705, rs10866276, rs12644280 and rs4635850 synthesized) were regarded as risk factors for IDCM patients when compared with carriers of other haplotypes (all P < .05). Furthermore, IDCM patients with two novel polymorphisms (c.731 + 131 T > G and c.1789‐3 C > T) had lower systolic blood pressure. In conclusion, these five synonymous polymorphisms might constitute a genetic background that increases the risk of the development of IDCM in the Chinese Han population.

Left Ventricular Noncompaction: A Distinct Genetic Cardiomyopathy?

Left ventricular noncompaction (LVNC) describes a ventricular wall anatomy characterized by prominent left ventricular (LV) trabeculae, a thin compacted layer, and deep intertrabecular recesses. Individual variability is extreme, and trabeculae represent a sort of individual "cardioprinting." By itself, the diagnosis of LVNC does not coincide with that of a "cardiomyopathy" because it can be observed in healthy subjects with normal LV size and function, and it can be acquired and is reversible. Rarely, LVNC is intrinsically part of a cardiomyopathy; the paradigmatic examples are infantile tafazzinopathies. When associated with LV dilation and dysfunction, hypertrophy, or congenital heart disease, the genetic cause may overlap. The prevalence of LVNC in healthy athletes, its possible reversibility, and increasing diagnosis in healthy subjects suggests cautious use of the term LVNC cardiomyopathy, which describes the morphology but not the functional profile of the cardiomyopathy.

RBM20 and RBM24 cooperatively promote the expression of short enh splice variants

PDZ-LIM protein ENH1 is a scaffold protein for protein kinases and transcriptional regulators. While ENH1 promotes the hypertrophic growth of cardiomyocytes, its short splice variant (ENH3) prevents the hypertrophic growth. The mechanism underlying the alternative splicing of enh mRNA between ENH short and long isoforms has remained unknown. Here, we found that two splicing factors, RNA-binding motif 20 (RBM20) and RNA-binding motif 24 (RBM24) together promoted the expression of short enh splice variants and bound the 5' intronic region of exon 11 containing an in-phase stop codon. In addition, expression of both RBMs is repressed by hypertrophic stimulations. Collectively, our results suggest that, in healthy conditions, RBM20 and RBM24 cooperate to promote the expression of short ENH isoforms.