rs375882485 — MYBPC3 Arg502Trp

MYBPC3 Arg502Trp — The Most Common Recurrent HCM Mutation

Cardiac myosin-binding protein C¹¹ Cardiac myosin-binding protein C
a large, modular protein encoded by MYBPC3 on chromosome 11p11.2 that integrates into the thick filament of the cardiac sarcomere, where it fine-tunes contraction by regulating myosin head positioning and cross-bridge cycling rate is the most frequently mutated protein in hypertrophic cardiomyopathy (HCM), accounting for roughly 40% of all genotype-positive cases. Among the hundreds of MYBPC3 pathogenic variants, the p.Arg502Trp missense mutation stands out: it is the single most recurrent HCM-causing point mutation identified in large European-descent cohorts, found in approximately 2.4% of all HCM patients screened. This variant is classified Pathogenic/Likely Pathogenic by 31 of 40 ClinVar submitters, with three-star expert review status.

The Mechanism

The MYBPC3 protein is built from ten immunoglobulin-like (Ig) and fibronectin-type III (FN3) domains²² immunoglobulin-like (Ig) and fibronectin-type III (FN3) domains
barrel-shaped protein folds numbered C0 through C10 from the N-terminus; the central C3-C6 region is one of the most common mutation hotspots in HCM. Arg502 sits on the surface of the C3 domain, positioned on a loop exposed to the cytoplasm. Unlike many HCM missense variants that destabilize the domain itself, the NMR structure of the Arg502Trp mutant C3 domain³³ NMR structure of the Arg502Trp mutant C3 domain
solved by Inchingolo et al. in 2014 using solution NMR spectroscopy, deposited as PDB 2MQ3 reveals preserved immunoglobulin-like folding — the domain remains structurally intact. Instead, replacing the positively charged, polar arginine with a bulky, hydrophobic tryptophan dramatically alters the electrostatic surface of C3. This change is predicted to disrupt binding between MYBPC3 and sarcomeric partner proteins that dock on this domain, corrupting the protein's regulatory role in cross-bridge cycling without affecting its incorporation into the sarcomere. The net result is an unrestrained, hypercontractile state characteristic of HCM: excessive myosin engagement, impaired relaxation, and ultimately cardiomyocyte hypertrophy, myofibrillar disarray, and interstitial fibrosis.

The Evidence

The foundational clinical study by Saltzman et al. (Circ Res, 2010)⁴⁴ Saltzman et al. (Circ Res, 2010) screened 1,414 unrelated HCM probands and identified Arg502Trp in 34 (2.4%) — the highest single-variant frequency in a large, unselected HCM cohort. Extending analysis to 17 families identified a total of 77 carriers. Family segregation yielded a calculated odds ratio of 11,000:1 for co-inheritance of the variant with HCM. Penetrance was age-dependent: roughly 50% of carriers lacked clinical evidence of HCM before age 45. Yet by age 50, approximately 30% of carriers had experienced a major adverse cardiac event (death, cardiac arrest, hemodynamically significant arrhythmia, or heart failure hospitalization). When Arg502Trp occurred alongside a second sarcomere gene mutation, 75% of carriers had a serious event before age 20 — a clinical severity approaching that of the most aggressive MYH7 mutations.

Haplotype analysis across all 17 families revealed at least 4 independent chromosomal backgrounds carrying the same mutation, indicating recurrent de novo origins rather than a single ancient founder. This explains why Arg502Trp appears broadly across European populations rather than clustering in a single ethnic group.

The 2024 AHA/ACC HCM guideline (Ommen et al., Circulation)⁵⁵ 2024 AHA/ACC HCM guideline (Ommen et al., Circulation) establishes the current management framework: all pathogenic sarcomere variant carriers require annual echocardiographic surveillance; symptomatic obstructive HCM should first receive beta-blockers or non-dihydropyridine calcium channel blockers, followed by mavacamten (FDA-approved 2022, Class I recommendation in 2024 guidelines) or disopyramide for refractory cases before considering invasive septal reduction therapy.

Practical Actions

For heterozygous Arg502Trp carriers, the practical priorities are: (1) establish baseline cardiovascular assessment with echocardiography, (2) commence annual surveillance even if currently asymptomatic — penetrance is age-dependent and over 50% of carriers will develop overt HCM by their sixth decade, (3) avoid competitive sport until HCM is excluded or appropriately risk-stratified, and (4) ensure all first-degree relatives are offered targeted genetic testing.

When obstructive HCM develops (resting or provoked left ventricular outflow tract gradient ≥30 mmHg), beta-blockers are the first-line treatment. Mavacamten, a cardiac-specific myosin inhibitor that directly reduces the proportion of force-generating myosin heads, is a guideline-endorsed second-line agent for obstructive HCM and operates upstream of the mutation by normalizing cross-bridge cycling — making it mechanistically well-suited for sarcomere protein variants including MYBPC3. Disopyramide added to beta-blockade is an alternative. Surgical septal myectomy at experienced HCM centres remains the reference standard for drug-refractory outflow obstruction.

ICD implantation is guided by formal sudden cardiac death (SCD) risk scoring (ESC HCM Risk-SCD calculator or AHA/ACC 5-year MACE estimate). A prior cardiac arrest, sustained ventricular tachycardia, family history of HCM-related SCD in first-degree relatives, maximal LV wall thickness ≥30 mm, non-sustained VT on Holter monitoring, and unexplained syncope are all established risk factors that should inform the shared decision regarding ICD.

Interactions

The clinical severity of MYBPC3 Arg502Trp increases substantially when a second pathogenic sarcomere variant is present (compound heterozygosity or double heterozygosity). Saltzman et al. reported that carriers of Arg502Trp plus a second sarcomere gene mutation had 75% major event rates before age 20 — indistinguishable from the most aggressive single-gene mutations. Any first-degree relative found to carry both this variant and an additional sarcomere pathogenic variant should be evaluated urgently by an HCM specialist. Other MYBPC3 pathogenic variants already in this database — including rs187830361 (Trp792Arg), rs193922385 (Arg177Cys), rs397514752 (Gly490Val), and rs36211723 (Asp770Asn) — represent independent HCM-causing mutations in MYBPC3; compound heterozygosity for two such mutations is rare but clinically severe.