The scale of the problem justifies the effort. Sudden cardiac death is characterized by high incidence, low survival rates, and, crucially, it often presents as the very first manifestation of an underlying cardiovascular disease. Studies cited in the review, including a 2025 analysis in the Journal of the American Heart Association of sudden cardiac death mortality in the United States between 1999 and 2022, and a 2025 study in JACC: Clinical Electrophysiology showing that sudden cardiac death is frequently the first sign of cardiovascular disease, underline how little opportunity clinicians have to intervene before the fatal arrhythmia strikes. Out-of-hospital survival rates remain low, and risk stratification tools, including electrocardiographic markers and clinical scores, capture only part of the danger. That gap has pushed researchers toward the genome and, more recently, the epigenome, in search of signals that identify vulnerable hearts before they fail.

The genetic story begins with common variation. The review summarizes single nucleotide polymorphisms and insertion/deletion variants associated with sudden cardiac death, discovered through two complementary strategies: candidate-gene studies, which examine genes chosen for their known roles in cardiac function, and genome-wide association studies, which scan the entire genome without prior assumptions. A recurring theme is that risk variants cluster in genes involved in cardiovascular function, signal transduction, and cellular metabolism. Among the candidates highlighted are variants in NOS1AP, CASQ2 and GPD1L associated with sudden death risk in coronary artery disease; polymorphisms in angiotensin-converting enzyme-related pathways; a TGFBR2 polymorphism linked to cardiac arrest risk; common variation in fatty acid metabolic genes; and a missense variant in the neuregulin 1 gene that, remarkably, has been associated with both schizophrenia and sudden cardiac death, hinting at shared biology between neural and cardiac electrical systems.

Insertion/deletion polymorphisms form a second, technically distinct layer of variation. These variants, in which short stretches of DNA are present or absent, can alter gene dosage, disrupt regulatory sequences, or change protein structure. The review catalogues a series of such variants reported largely in Chinese populations, including indels in CTH, HSPA1B, the 3′ untranslated region of COL1A2, STIM1, COX10, NPC1, DSG2, LTBP4, the MIR155HG locus, the 3’UTR of STAT5A, and the alpha2-adrenergic receptor gene, the latter identified in Finnish cohorts as a genetic risk factor for sudden cardiac death. Several of these variants sit in regulatory regions rather than coding sequences, which means their functional impact likely operates through altered gene expression, a mechanism that connects naturally to the epigenetic half of the review.

Genome-wide association studies have added their own landmarks. A protective locus at GPC5 was identified in 2010; a susceptibility locus at chromosome 2q24.2 was mapped in individuals of European ancestry in 2011; and subsequent efforts, including a comprehensive 2018 evaluation of the genetic architecture of sudden cardiac arrest published in the European Heart Journal, have refined the picture. Yet the review is candid about a persistent problem: missing heritability. Known variants explain only a fraction of the familial clustering and population-level risk that epidemiologists observe, a challenge familiar across complex-disease genetics since the influential 2009 Nature paper by Manolio and colleagues. Rare variants, gene-gene interactions, gene-environment interactions, and epigenetic modifications are all candidate explanations for the unexplained portion, and the Moscow team argues that only large-scale, integrative, multi-ethnic studies combining genomic, epigenomic and clinical data with functional validation will close the gap.

That argument leads directly to epigenetics, the layer of molecular regulation that changes gene activity without altering the DNA sequence itself. The review focuses on three principal mechanisms: microRNAs, DNA methylation, and histone modifications. MicroRNAs are short non-coding RNAs that bind target messenger RNAs and suppress their translation or trigger their degradation. In the cardiovascular system they are pervasive regulators, controlling everything from cardiac conduction to fibrosis. The classic example, miR-1, regulates the arrhythmogenic potential of the heart by targeting the gap junction gene GJA1 and the potassium channel gene KCNJ2, directly linking microRNA levels to the electrical stability of the myocardium. Other microRNAs, including members of the miR-29, miR-133 and miR-30 families, modulate cardiac fibrosis and matrix remodeling, processes that create the structural substrate for lethal arrhythmias.

What makes microRNAs especially attractive for sudden cardiac death research is their measurability in body fluids. Tissue-based microRNAs recovered from post-mortem heart samples and circulating microRNAs detected in plasma both act as mechanistic regulators of the disease process and have emerged as exploratory biomarker candidates. Studies have reported that miR-1, miR-499 and miR-208 are sensitive markers for diagnosing sudden death due to early acute myocardial infarction; that miR-3113-5p, miR-223-3p, miR-133a-3p and miR-499a-5p can discriminate sudden cardiac death; and that plasma extracellular vesicle microRNA-208b-3p and microRNA-143-3p show promise as predictive biomarkers in acute coronary syndrome. Circulating microRNAs have even been examined in relation to sudden death risk in patients with coronary heart disease and to outcomes after cardiac arrest. The forensic dimension is equally striking: quantitative analysis of miR-1, miR-133a and miR-26a in heart tissue and whole blood has been proposed as a tool to help pathologists differentiate causes of death when autopsies are inconclusive.

The review, however, refuses to oversell these findings. It notes that inconsistent directions of association, methodological heterogeneity, and limited independent validation currently preclude the clinical application of microRNA biomarkers. Different studies measure different microRNA panels in different sample types with different normalization strategies, and few results have been replicated in independent cohorts. DNA methylation studies of sudden cardiac death are even scarcer, but they suggest potential roles for imprinted genes and oxidative stress pathways. One notable thread involves Prader-Willi syndrome, an imprinting disorder in which cardiac causes of death are overrepresented; recent work shows that deficiency of the necdin gene, lost in the syndrome, attenuates cardiac contractility, and that loss of Snord116 protects cardiomyocyte kinetics during ischemic stress, providing mechanistic links between imprinted loci and cardiac vulnerability. Differential methylation in the GSTT1 regulatory region has also been reported in sudden unexplained death, pointing toward detoxification and oxidative stress as methylation-sensitive pathways relevant to arrhythmic risk.

Histone modifications and chromatin remodeling represent the most underexplored but most promising frontier. Histone acetylation and deacetylation, mediated by histone acetyltransferases and histone deacetylases, reshape chromatin accessibility and thereby tune the expression of entire gene programs. Experimental work has shown that class I HDACs regulate angiotensin II-dependent cardiac fibrosis, that the stress-activated kinase MKK7 governs the epigenetics of cardiac repolarization and arrhythmia prevention, and that HDAC3 and HDAC5 influence cardiac conduction disease and mitochondrial function through their control of transcription factors such as Nkx2.5, MEF2 and PGC-1alpha. A 2025 experimental study even used the DNA damage marker gamma-H2AX to detect DNA damage in heart tissue from sudden cardiac death victims, suggesting that chromatin-level injury signatures may be readable in post-mortem material. These findings remain at the level of mechanism rather than validated clinical markers, but they sketch a plausible route by which environmental stressors, from ischemia to toxic exposures, become permanently inscribed in cardiac chromatin and translate into electrical instability.

The overall message of the review is one of cautious momentum. The genetic and epigenetic landscape of non-familial sudden cardiac death is no longer blank: common and rare variants, regulatory indels, circulating microRNAs, methylation patterns and chromatin modifiers all contribute pieces to the puzzle. But the pieces do not yet assemble into a predictive model that a cardiologist could apply at the bedside, and the authors are explicit that translating these molecular insights into clinical practice will require large-scale, integrative and multi-ethnic studies that combine genomic, epigenomic and clinical data with functional validation. Until then, the review serves as both a map of what is known and a checklist of what remains undone, and it makes a compelling case that the missing heritability of sudden cardiac death may be hiding, at least in part, not in the sequence of the genome but in the chemical marks written upon it.

Subject of Research: Genetic and epigenetic determinants of non-familial sudden cardiac death

Article Title: Genetic and epigenetic landscape of non-familial sudden cardiac death

Article References: Natalia, B., Natalia, M., Maxim, K., Olga, F., & Ivan, K. (2026). Genetic and epigenetic landscape of non-familial sudden cardiac death. Molecular Biology Reports, 53(1), Article 1630. https://doi.org/10.1007/s11033-026-12821-8

Image Credits: AI Generated

DOI: 10.1007/s11033-026-12821-8

Keywords: sudden cardiac death, genetic variants, single nucleotide polymorphism, insertion-deletion polymorphism, genome-wide association study, epigenetics, microRNA, DNA methylation, histone modification, chromatin remodeling, missing heritability, cardiac arrhythmia