rs397516919 — DSP DSP Trp550Ter

DSP Trp550Ter — An Early Break in the Cardiac Scaffolding

The heart beats more than 2.5 billion times over a lifetime. Sustaining that rhythm requires adhesion structures strong enough to withstand constant mechanical stress — and the primary load-bearing junction between adjacent cardiac muscle cells is the desmosome¹¹ desmosome
protein complex that acts as a molecular rivet at sites of peak tension in cardiomyocytes. Desmoplakin (DSP) is the central structural element of the desmosome, linking the desmosomal plaque to the intermediate filament cytoskeleton inside the cell. The Trp550Ter variant — a G-to-A substitution at chromosome 6 position 7,570,512 — converts codon 550 from tryptophan to a stop signal, truncating the protein at less than 19% of its full 2,872-amino-acid length and eliminating its entire functional architecture.

The Mechanism

The c.1650G>A substitution converts the tryptophan codon (TGG) to a stop codon (TGA) at position 550, near the start of desmoplakin's central plakin domain. The resulting truncated transcript is expected to undergo nonsense-mediated mRNA decay²² nonsense-mediated mRNA decay
a cellular surveillance pathway that degrades mRNAs containing premature stop codons, preventing production of potentially toxic truncated proteins, eliminating functional desmoplakin from the affected allele. The consequence is haploinsufficiency — roughly half the normal DSP output from a single intact copy. With codon 550 in the N-terminal region, this truncation is particularly severe: the entire plakin domain, both spectrin repeats, and the C-terminal intermediate-filament-binding domain are lost. Desmosomal junctions with only half the normal desmoplakin cannot maintain adhesion under the cyclic mechanical load of cardiac contraction. Cells detach; the heart patches the torn junctions with scar tissue; the resulting fibrosis creates a pro-arrhythmic substrate.

DSP-related arrhythmogenic cardiomyopathy (DSP-ACM) is clinically distinct from the classical right-dominant arrhythmogenic right ventricular cardiomyopathy (ARVC). In a landmark series of 107 DSP-mutation patients, 55% showed exclusively left ventricular involvement versus 0% of PKP2-mutation carriers³³ 55% showed exclusively left ventricular involvement versus 0% of PKP2-mutation carriers. Episodic myocarditis-like events — chest pain, troponin elevation, and cardiac MRI changes indistinguishable from acute myocarditis — occur in 14–22% of carriers, often as the first clinical presentation, and significantly accelerate downstream fibrosis and arrhythmia risk.

The Evidence

Three large studies define the clinical burden of DSP pathogenic variants. Gasperetti et al. (European Heart Journal, 2025)⁴⁴ Gasperetti et al. (European Heart Journal, 2025) followed 800 DSP variant carriers across 26 institutions and documented sustained ventricular arrhythmia in 17.4% (3.9% per year). A striking 32.5% of carriers did not meet established diagnostic criteria for any cardiomyopathy subtype, illustrating how easily DSP-ACM escapes standard workup. Myocardial injury episodes increased ventricular arrhythmia risk 2.4-fold and heart failure hospitalizations 5.1-fold.

Hoorntje et al. (Circ Genomic Precis Med, 2023)⁵⁵ Hoorntje et al. (Circ Genomic Precis Med, 2023) demonstrated that among 170 individuals with DSP truncating variants, 33% experienced major ventricular arrhythmia. Crucially, variants in positions expected to trigger nonsense-mediated decay — which the Trp550Ter variant almost certainly does, given its N-terminal location — were independently associated with higher arrhythmic risk compared with truncating variants that escape decay. The earlier the stop codon, the less likely a stable partial protein escapes.

Jacobsen et al. (Heart Rhythm, 2025)⁶⁶ Jacobsen et al. (Heart Rhythm, 2025) showed that among 100 DSP variant carriers, those engaging in high-level endurance activity had a 2.37-fold increased risk of myocardial injury episodes; each such episode predicted subsequent arrhythmia with a hazard ratio of 7.86 and heart failure with a hazard ratio of 10.28. Vigorous endurance sports are an environmental modifier that accelerates disease expression.

Practical Actions

Heterozygous carriers require cardiac surveillance even without symptoms. Baseline evaluation includes cardiac MRI with late gadolinium enhancement (the primary tool for detecting early LV fibrosis before ejection fraction falls), 24–48-hour Holter monitoring for PVC burden and non-sustained VT, and a resting ECG. Specialists typically recommend annual to biennial surveillance thereafter, with accelerated imaging after any episode of chest pain or troponin elevation. High-intensity competitive sport should be assessed individually with a cardiologist before continuing. First-degree relatives carry a 50% probability of inheriting the variant and should undergo cascade genetic testing.

Interactions

DSP-ACM risk is amplified by additional desmosomal gene variants. Carrying pathogenic variants in two desmosomal genes simultaneously — compound digenic inheritance — is associated with earlier onset and more severe phenotype. Relatives carrying both this DSP variant and a pathogenic variant in PKP2 (rs111517471) or DSG2 warrant particularly intensive surveillance. Physical activity level is the most important environmental modifier: endurance athletes with desmosomal variants develop cardiomyopathy at substantially higher rates and earlier ages than sedentary carriers, a finding now reflected in cardiology society guidance discouraging competitive sport pending formal evaluation.