Heritable cardiac conduction and myocardial disease: from the clinic to the basic science laboratory and back to the clinic

A very long-term observation of a family with dilated cardiomyopathy and overlapping phenotype from lamin A/C mutation

AIMS

We aim to describe one of the longest longitudinal follow-ups reported so far (>22 years), concerning a whole family affected by a missense lamin A/C mutation (Arg60Gly), which manifested as an overlapping phenotype with cardiac and extracardiac involvement over time.

METHODS

Starting from the family history, two generations of that family were prospectively observed, from 1997 until 2020. At baseline, four individuals with dilated cardiomyopathy and cardiac conduction defects showed the same mutation. This was also found in three young individuals, phenotypically unaffected at baseline assessment.

RESULTS

The prolonged clinical and laboratory evaluation has shown the evolution of an overlapping phenotype in which cardiac alterations have been associated with lipodystrophy and neurological manifestations. In the first observed generation, the prognosis was negatively affected by the progression of heart failure and lipodystrophy, whereas in the second generation the first phenotypic manifestations became evident after the 2nd decade. Cardiac magnetic resonance played a relevant role in the early detection of cardiac alteration. Right bundle branch block was another sign of initial phenotypical expression.

CONCLUSION

In lamin A/C gene mutation carriers, a strict, multidisciplinary follow-up allows the opportunity to monitor the progress of the disease and to intervene precociously with the best available treatments.

Exome Sequencing Identifies a Novel LMNA Splice-Site Mutation and Multigenic Heterozygosity of Potential Modifiers in a Family with Sick Sinus Syndrome, Dilated Cardiomyopathy, and Sudden Cardiac Death

The goals are to understand the primary genetic mechanisms that cause Sick Sinus Syndrome and to identify potential modifiers that may result in intrafamilial variability within a multigenerational family. The proband is a 63-year-old male with a family history of individuals (>10) with sinus node dysfunction, ventricular arrhythmia, cardiomyopathy, heart failure, and sudden death. We used exome sequencing of a single individual to identify a novel LMNA mutation and demonstrated the importance of Sanger validation and family studies when evaluating candidates. After initial single-gene studies were negative, we conducted exome sequencing for the proband which produced 9 gigabases of sequencing data. Bioinformatics analysis showed 94% of the reads mapped to the reference and identified 128,563 unique variants with 108,795 (85%) located in 16,319 genes of 19,056 target genes. We discovered multiple variants in known arrhythmia, cardiomyopathy, or ion channel associated genes that may serve as potential modifiers in disease expression. To identify candidate mutations, we focused on ~2,000 variants located in 237 genes of 283 known arrhythmia, cardiomyopathy, or ion channel associated genes. We filtered the candidates to 41 variants in 33 genes using zygosity, protein impact, database searches, and clinical association. Only 21 of 41 (51%) variants were validated by Sanger sequencing. We selected nine confirmed variants with minor allele frequencies <1% for family studies. The results identified LMNA c.357-2A>G, a novel heterozygous splice-site mutation as the primary mutation with rare or novel variants in HCN4, MYBPC3, PKP4, TMPO, TTN, DMPK and KCNJ10 as potential modifiers and a mechanism consistent with haploinsufficiency.

Genetic cardiomyopathies. Lessons learned from humans, mice, and zebrafish

Dilated cardiomyopathy (DCM) is a multifactorial disease of the heart muscle and a leading cause of congestive heart failure. Human genetic studies and the establishment of suitable animal models such as mice and zebrafish have already revealed parts of its genetic etiology. With the next generation of genomic sequencing technologies (NGS) on the rise, the comprehensive genetic dissection of DCM patients will reveal clinically relevant information, novel causes, and modifiers of this complex disorder. The recent exploration of the epigenome as another mechanism of cardiac gene regulation will further elucidate unexplained variations observed in the correlation between the patient's genotype and phenotype. Some of these intriguing advances being made in basic genetic research will soon find their way into clinical practice for more individualized treatment of cardiomyopathy patients.

Beyond membrane channelopathies: alternative mechanisms underlying complex human disease

Over the past fifteen years, our understanding of the molecular mechanisms underlying human disease has flourished in large part due to the discovery of gene mutations linked with membrane ion channels and transporters. In fact, ion channel defects ("channelopathies" - the focus of this review series) have been associated with a spectrum of serious human disease phenotypes including cystic fibrosis, cardiac arrhythmia, diabetes, skeletal muscle defects, and neurological disorders. However, we now know that human disease, particularly excitable cell disease, may be caused by defects in non-ion channel polypeptides including in cellular components residing well beneath the plasma membrane. For example, over the past few years, a new class of potentially fatal cardiac arrhythmias has been linked with cytoplasmic proteins that include sub-membrane adapters such as ankyrin-B (ANK2), ankyrin-G (ANK3), and alpha-1 syntrophin, membrane coat proteins including caveolin-3 (CAV3), signaling platforms including yotiao (AKAP9), and cardiac enzymes (GPD1L). The focus of this review is to detail the exciting role of lamins, yet another class of gene products that have provided elegant new insight into human disease.