Determining the Likelihood of Disease Pathogenicity Among Incidentally Identified Genetic Variants in Rare Dilated Cardiomyopathy-Associated Genes

Exploring and Expanding Secondary Findings Through Exome Sequencing in the Turkish Population

INTRODUCTION

Exome-sequencing (ES) methods enable accurate diagnosis in challenging cases and uncover secondary findings (SFs) potentially linked to life-threatening or preventable diseases. The American College of Medical Genetics and Genomics (ACMG) publishes a list detailing which SFs should be reported and regularly updates it. We aimed to compare results across different SF versions in patients and explore additional SFs to identify potential new recommendations for SF reporting.

METHODS

We conducted a retrospective analysis of 724 patients to identify ACMG SFs using the QIAGEN Clinical Insight (QCI) Interpret database. Furthermore, we investigated pathogenic/likely pathogenic variants in cancer and cardiovascular disease genes not listed in ACMG SFs, as well as genes associated with common diseases prevalent in our country.

METHODS

ACMG SF v3.2 variants were identified in 56 patients (7.7%), with no observed differences between ACMG v3.1 and v3.2. Additionally, our analysis revealed that 208 patients harbored non-ACMG SF variants.

CONCLUSION

In this study, we focused on known SFs and identified additional variants that could be considered as new recommendations. While expanding the list of SFs can pose challenges during analyses and genetic counseling, a thoughtfully curated SF list has the potential to enhance patient care and improve clinical outcomes.

The clinical and genetic spectrum of pediatric hypertrophic cardiomyopathy manifesting before one year of age

BACKGROUND

Hypertrophic cardiomyopathy (HCM) presents a wide range of clinical scenarios depending on the age of manifestation, with a less favorable prognosis in children. The genetic spectrum and clinical causes of HCM diagnosed before one year of age is rarely reported.

METHODS

We analyzed the genetic causes and genotype-phenotype correlations in 68 children diagnosed with HCM during the first year of life. Genetic analysis was performed using targeted gene sequencing (39 HCM-related genes), followed by whole-exome sequencing for genotype-negative cases. The genetic data were correlated with clinical characteristics, disease progression, and prognosis.

RESULTS

The overall genotype-positive rate was 81%, with an equal proportion of sarcomeric (29%) and RAS-related genetic cases (29%). Gestational diabetes in mothers was more frequently observed in children with variants in Z-disc-related genes. Overall, one year-survival rate from all causes was 91.2%, with the best survival outcomes associated with sarcomeric and Z-disk-related gene variants.

CONCLUSION

HCM manifesting in children before one year of age showed an approximately equal proportion of sarcomeric and RAS cascade-related cases. A more favorable prognosis was associated with sarcomeric mutations; whereas metabolic gene-related HCM cases were characterized by the highest one-and five-year mortality due to heart failure.

IMPACT

We analyzed the genetic causes and genotype-phenotype correlations in 68 children diagnosed with HCM during the first year of life. Patients with sarcomeric mutations demonstrated a more favorable prognosis, whereas metabolic gene-related HCM cases were the highest one- and five-year mortality rates due to HF. We identified several factors associated with unfavorable outcomes, including LV thickness, HF class, elevated troponin, increased NT-proBNP levels, and RV hypertrophy. We proposed several new and previously unreported genes, such as ROBO4 and KMT2D, as potentially causative for infantile HCM. The true role of these genes in this disease requires confirmation.

Mechanisms of RBM20 Cardiomyopathy: Insights From Model Systems

RBM20 (RNA-binding motif protein 20) is a vertebrate- and muscle-specific RNA-binding protein that belongs to the serine-arginine-rich family of splicing factors. The RBM20 gene was first identified as a dilated cardiomyopathy-linked gene over a decade ago. Early studies in Rbm20 knockout rodents implicated disrupted splicing of RBM20 target genes as a causative mechanism. Clinical studies show that pathogenic variants in RBM20 are linked to aggressive dilated cardiomyopathy with early onset heart failure and high mortality. Subsequent studies employing pathogenic variant knock-in animal models revealed that variants in a specific portion of the arginine-serine-rich domain in RBM20 not only disrupt splicing but also hinder nucleocytoplasmic transport and lead to the formation of RBM20 biomolecular condensates in the sarcoplasm. Conversely, mice harboring a disease-associated variant in the RRM (RNA recognition motif) do not show evidence of adverse remodeling or exhibit sudden death despite disrupted splicing of RBM20 target genes. Thus, whether disrupted splicing, biomolecular condensates, or both contribute to dilated cardiomyopathy is under debate. Beyond this, additional questions remain, such as whether there is sexual dimorphism in the presentation of RBM20 cardiomyopathy. What are the clinical features of RBM20 cardiomyopathy and why do some individuals develop more severe disease than others? In this review, we summarize the reported observations and discuss potential mechanisms of RBM20 cardiomyopathy derived from studies employing in vivo animal models and in vitro human-induced pluripotent stem cell-derived cardiomyocytes. Potential therapeutic strategies to treat RBM20 cardiomyopathy are also discussed.

VEZF1 loss-of-function mutation underlying familial dilated cardiomyopathy

Dilated cardiomyopathy (DCM), characteristic of left ventricular or biventricular dilation with systolic dysfunction, is the most common form of cardiomyopathy, and a leading cause of heart failure and sudden cardiac death. Aggregating evidence highlights the underlying genetic basis of DCM, and mutations in over 100 genes have been causally linked to DCM. Nevertheless, due to pronounced genetic heterogeneity, the genetic defects underpinning DCM in most cases remain obscure. Hence, this study was sought to identify novel genetic determinants of DCM. In this investigation, whole-exome sequencing and bioinformatics analyses were conducted in a family suffering from DCM, and a novel heterozygous mutation in the VEZF1 gene (coding for a zinc finger-containing transcription factor critical for cardiovascular development and structural remodeling), NM_007146.3: c.490A > T; p.(Lys164*), was identified. The nonsense mutation was validated by Sanger sequencing and segregated with autosome-dominant DCM in the family with complete penetrance. The mutation was neither detected in another cohort of 200 unrelated DCM patients nor observed in 400 unrelated healthy individuals nor retrieved in the Single Nucleotide Polymorphism database, the Human Gene Mutation Database and the Genome Aggregation Database. Biological analyses by utilizing a dual-luciferase reporter assay system revealed that the mutant VEZF1 protein failed to transactivate the promoters of MYH7 and ET1, two genes that have been associated with DCM. The findings indicate VEZF1 as a new gene responsible for DCM, which provides novel insight into the molecular pathogenesis of DCM, implying potential implications for personalized precisive medical management of the patients affected with DCM.

Identification of BMP10 as a Novel Gene Contributing to Dilated Cardiomyopathy

Dilated cardiomyopathy (DCM), characterized by left ventricular or biventricular enlargement with systolic dysfunction, is the most common type of cardiac muscle disease. It is a major cause of congestive heart failure and the most frequent indication for heart transplantation. Aggregating evidence has convincingly demonstrated that DCM has an underlying genetic basis, though the genetic defects responsible for DCM in a larger proportion of cases remain elusive, motivating the ongoing research for new DCM-causative genes. In the current investigation, a multigenerational family affected with autosomal-dominant DCM was recruited from the Chinese Han population. By whole-exome sequencing and Sanger sequencing analyses of the DNAs from the family members, a new BMP10 variation, NM_014482.3:c.166C > T;p.(Gln56*), was discovered and verified to be in co-segregation with the DCM phenotype in the entire family. The heterozygous BMP10 variant was not detected in 268 healthy volunteers enrolled as control subjects. The functional measurement via dual-luciferase reporter assay revealed that Gln56*-mutant BMP10 lost the ability to transactivate its target genes NKX2.5 and TBX20, two genes that had been causally linked to DCM. The findings strongly indicate BMP10 as a new gene contributing to DCM in humans and support BMP10 haploinsufficiency as an alternative pathogenic mechanism underpinning DCM, implying potential implications for the early genetic diagnosis and precision prophylaxis of DCM.