The 98% We Ignored May Rewrite Cardiology

Key Takeaway: While the vast majority of human DNA does not code for proteins, mounting evidence shows these non-coding regions—the so-called ‘dark genome’—actively regulate cardiovascular health and disease. This emerging understanding is opening the door to novel diagnostic tools and RNA-based therapies that could fundamentally change how we prevent and treat heart conditions.

From ‘Junk DNA’ to a Gold Mine

For decades, scientists focused on just 2% of our DNA: the protein-coding genes that seemingly held all the power. The remaining 98% was largely dismissed as an evolutionary remnant, meaningless biological filler. Researchers even coined the term “junk DNA.” This label is now proving to be a colossal misconception. A growing body of evidence shows that this vast expanse of genetic material, sometimes called the “dark genome,” is anything but silent. It is a masterful regulatory layer that quietly orchestrates the behavior of all cells in the body, including those in the heart and blood vessels. Considering that cardiovascular diseases remain the leading cause of death globally, claiming nearly 18 million lives annually, understanding this hidden dimension of our biology has never been more urgent.^[2]

The Scope of the Review

A comprehensive review published in the cardiovascular literature synthesized the current body of knowledge on the dark genome’s role in heart disease.^[1] This work did not represent a single experiment but a broad literature review—an academic effort to map what we know, what we suspect, and where the field is headed. The authors examined how non-coding DNA elements, particularly a class of molecules called non-coding RNAs (ncRNAs), influence cardiovascular pathology. They also discussed how advances in genome-wide association studies (GWAS) and other high-throughput technologies are finally drawing clearer lines between the genome’s non-coding regions and specific cardiovascular traits like blood pressure, atherosclerosis, and heart failure.

The review highlighted several key themes. First, non-coding RNAs are not passive bystanders but active regulators of gene expression in the cardiovascular system. Second, our mechanistic understanding of how specific dark genome elements contribute to disease is rapidly maturing. And third, this knowledge is already spurring the development of novel targeted therapeutics—especially RNA-based medicines. These new drugs hold the potential to intervene in cardiovascular diseases with a level of specificity we have never had before.

Mechanism: How the Dark Genome Works

To grasp the significance of this topic, it helps to refresh our basic understanding of molecular biology. Your DNA is essentially a lengthy instruction manual. The protein-coding genes, that famous 2%, are the chapters that directly tell cells how to build enzymes, structural proteins, and signaling molecules. But the dark genome? Think of it as an editorial layer: the punctuation, the marginalia, the instructions that tell a cell when to read a chapter, how loudly, and when to stop.

Non-coding RNAs are among the most important products of this regulatory layer. For instance, microRNAs (miRNAs) are tiny RNA molecules, only about 22 nucleotides long, that can bind to the messenger RNAs of specific genes, preventing them from being translated into protein.^[3] Long non-coding RNAs (lncRNAs), which are over 200 nucleotides long, take on even more diverse roles: they can shuttle protein complexes to specific regions of DNA, support three-dimensional chromatin architecture, and modulate inflammatory signaling pathways.^[4]

In the cardiovascular system, these molecules have been shown to play a role in nearly every stage of disease. Certain miRNAs regulate the proliferation and migration of vascular smooth muscle cells, a process central to the formation of atherosclerotic plaques.^[5] Others modulate the fibrotic response in the heart after a myocardial infarction, influencing whether damaged tissue heals with functional muscle or stiff scar tissue. The lncRNA ANRIL, located in a chromosomal region (9p21) strongly associated with coronary artery disease risk in GWAS studies, appears to regulate inflammatory gene expression in vascular endothelial cells.^[6] For years, the 9p21 locus was a mystery—it was one of the strongest genetic signals for heart disease, yet it contained no protein-coding genes. ANRIL helped solve that puzzle.

The genome’s regulatory architecture is not just about linear RNA sequences; the three-dimensional organization within the nucleus and alternative splicing processes directly determine heart morphology. Topologically associated domains (TADs) are molecular boundaries that prevent enhancers from triggering the wrong genes; the breakdown of these boundaries leads to severe clinical conditions like cardiac laminopathies. Similarly, mutations in non-coding intronic regions can cause the giant titin (TTN) gene, which builds the primary backbone of the sarcomere, to be improperly spliced, producing truncated protein isoforms (TTNtv). The result is a loss of myocardial elasticity and dilated cardiomyopathy, a condition frequently encountered in clinical practice. Furthermore, transposons—mobile sequences that are remnants of retroviruses and make up about 45% of the human genome—particularly the LINE-1 retrotransposon, directly trigger vascular calcification and atherosclerotic plaque hardening. Meanwhile, pseudogenes like APOOP1, ZNF542P, and PTENP1 quietly modulate intracellular cholesterol balance and the variability of patient responses to simvastatin.

Enhancer regions, non-coding DNA stretches that enhance the expression of distant genes, add another layer to this complexity. Variants in cardiac enhancers can subtly alter the expression of genes critical for heart development and rhythm, contributing to conditions like atrial fibrillation and congenital heart defects.^[7]

The dark genome’s repertoire extends beyond microRNAs and lncRNAs. Other members of this orchestra include small fragments derived from transfer RNAs (tsRNAs) during cellular stress, snoRNAs that manage ribosomal modifications, and circular RNAs (circRNAs), which, with their durable, covalently closed structures, accelerate cellular senescence. For example, in pressure overload-induced heart failure, circSlc8a1 accelerates pathological hypertrophy, while in the endothelium, circHIPK3 promotes vascular repair. The most paradigm-shifting discovery is the concept of the “dark proteome”: some RNA transcripts long considered silent and non-coding have been shown to harbor short open reading frames (smORFs) of less than 100 codons, releasing biologically potent micropeptides like DWORF or MOXI. These micropeptides directly influence the heart’s contractile strength and energy metabolism by acting on calcium pumps (SERCA2a) in the cardiomyocyte sarcoplasmic reticulum and on mitochondrial fatty acid beta-oxidation.

New Therapeutic Horizons

Perhaps the most exciting takeaway from this review is what the dark genome means for treatment. Traditional drug development has overwhelmingly targeted proteins—enzymes to inhibit, receptors to block. But if a disease is driven at the regulatory level by non-coding RNAs, then we need tools that operate at that level. RNA-based therapeutics, such as antisense oligonucleotides (ASOs) and small interfering RNAs (siRNAs), are designed to do just that. These molecules can selectively silence or modulate specific RNA molecules with extraordinary precision. Inclisiran, an FDA-approved siRNA that targets PCSK9 messenger RNA to lower LDL cholesterol, is an early proof that this approach works in cardiovascular medicine.^[8]

But the revolution isn’t limited to silencing protein-coding genes; molecules that directly target non-coding regulatory RNAs are already reaching clinical phases. In patients with heart failure with reduced ejection fraction (HFrEF) following myocardial infarction, CDR132L, an antisense oligonucleotide that suppresses the miR-132-3p molecule, unleashed the FOXO3 and SERCA2A pathways at the cellular level, which enhanced myocardial contractility, regressed hypertrophy, and achieved a 23.3% clinical reduction in median NT-proBNP levels in a Phase 1b trial (the Phase 2 HF-REVERT study is ongoing). MRG110, which targets the anti-angiogenic miR-92a-3p, increases endothelial SIRT1 and KLF2/KLF4 expression, triggering vascular regeneration and wound healing in the setting of ischemia. Similarly, ASOs like HTX-001, which targets the lncRNA WISPER with high specificity for cardiac fibroblasts, aim to halt myocardial fibrosis. Meanwhile, delivering synthetic Y-RNA fragments (EV-YF1 and yREX3) isolated from cardiosphere-derived extracellular vesicles to macrophages via lipid nanoparticles creates a potent cardioprotective shield that alleviates post-myocardial infarction reperfusion injury and inflammation.

As our map of the dark genome becomes more detailed, the number of potential therapeutic targets will increase dramatically. Circulating non-coding RNAs are also being investigated as biomarkers—blood-based signals that could detect heart disease earlier and more accurately than current tools.

Noteworthy Limitations

As with any emerging field, it is wise to remain cautious. This is a narrative review, not a meta-analysis or randomized controlled trial, so it reflects the authors’ interpretation of a rapidly evolving area. Many of the described mechanistic insights come from cell culture or animal models, and translating these findings to human patients remains a significant challenge. The sheer complexity of non-coding regulation—where thousands of ncRNAs interact in overlapping networks—means that targeting one molecule could have unintended downstream effects. RNA-based drugs also face practical hurdles, such as delivery to specific tissues and long-term safety.

Methodologically, the primary technical bottleneck in illuminating the dark genome is tissue heterogeneity. In cardiac tissue analyses, conventional bulk RNA sequencing averages the signal across cardiomyocytes, fibroblasts, endothelial cells, and immune cells, masking critical cell-specific ncRNA activities. The inability of common single-cell sequencing platforms to capture non-poly(A) tailed circular RNAs or small ncRNAs necessitates the standardization of long-read and total-RNA protocols. More importantly, unlike protein-coding genes, the genetic conservation of dark genome elements like lncRNAs between species is quite poor. The failure of an effect observed in rodent models to translate to the human myocardium is one of the most formidable hurdles in translational research; this requires the integration of functional non-coding variants into clinical risk prediction models and the development of tissue-specific targeted RNA delivery systems.

Final Assessment: The Future Perspective

The dark genome is no longer dark. It is a vast and intricate regulatory landscape that shapes cardiovascular health in ways we are only beginning to comprehend. For patients, this shift in understanding carries a powerful promise: heart disease is not just a problem of cholesterol levels and blood pressure readings; it is also a matter of molecular switches hidden deep within our genetic code. As RNA-based diagnostics and therapeutics mature, we will likely see a new generation of cardiovascular interventions—ones that target disease not at the protein level, but at its regulatory roots. The 98% of our DNA we once ignored may just be the most important part of the story.

Scientific Sources

1. Kesidou D, et al. The dark genome in cardiovascular medicine. European heart journal. 2026;47(33):4574-4592. PubMed: https://pubmed.ncbi.nlm.nih.gov/42425504/
2. Roth GA, et al. Global Burden of Cardiovascular Diseases and Risk Factors, 1990-2019: Update From the GBD 2019 Study. J Am Coll Cardiol. 2020. DOI: 10.1016/j.jacc.2020.11.010
3. Bartel DP. MicroRNAs: genomics, biogenesis, mechanism, and function. Cell. 2004. DOI: 10.1016/s0092-8674(04)00045-5
4. Rinn JL, et al. Genome regulation by long noncoding RNAs. Annu Rev Biochem. 2012. DOI: 10.1146/annurev-biochem-051410-092902
5. Cordes KR, et al. miR-145 and miR-143 regulate smooth muscle cell fate and plasticity. Nature. 2009. DOI: 10.1038/nature08195
6. Holdt LM, et al. ANRIL expression is associated with atherosclerosis risk at chromosome 9p21. Arterioscler Thromb Vasc Biol. 2010. DOI: 10.1161/ATVBAHA.109.196832
7. Dickel DE, et al. Genome-wide compendium and functional assessment of in vivo heart enhancers. Nat Commun. 2016. DOI: 10.1038/ncomms12923
8. Ray KK, et al. Two Phase 3 Trials of Inclisiran in Patients with Elevated LDL Cholesterol. N Engl J Med. 2020. DOI: 10.1056/NEJMoa1912387