A targeted therapy already transforming treatment for hypertrophic cardiomyopathy (HCM) may be effective across a broader range of disease-causing genetic mutations than previously understood, according to new preclinical research published in Nature Cardiovascular Research.
The study identifies a previously unknown molecular mechanism underlying one of the most common inherited forms of HCM and demonstrates that the cardiac myosin inhibitor mavacamten—the first targeted therapy available for this condition—can reverse disease-associated changes, even when the underlying biology differs from that of the patients for whom the drug was originally developed.
HCM affects approximately one in 200 to 500 people and is the leading cause of sudden cardiac death in young adults and athletes. The disease is characterized by abnormal thickening of the heart muscle, impaired relaxation, and excessive contractility, which can ultimately lead to heart failure, arrhythmias, and sudden cardiac death.
Most inherited cases are caused by variants in either MYH7, which encodes the molecular motor myosin, or MYBPC3, which encodes cardiac myosin-binding protein C (cMyBP-C), an important regulator of cardiac muscle contraction.
While truncating mutations in MYBPC3 reduce levels of cMyBP-C and promote excessive myosin activity, much less has been known about how missense mutations—which preserve protein levels but alter protein function—drive disease.
To investigate this question, researchers generated a knock-in mouse model carrying the R502W missense mutation, one of the most common pathogenic MYBPC3 variants found in patients with HCM. Unlike mice lacking cMyBP-C, the R502W animals maintained normal amounts and localization of the protein yet still developed hallmark features of hypertrophic cardiomyopathy, including cardiac hypertrophy, fibrosis, impaired cardiac function, and hypercontractility.
“Our findings support that mutation-induced loss of interactions between the central domains of cMyBP-C and myosin is a molecular pathomechanism in HCM that can be targeted by myosin inhibitors,” the authors write.
Rather than reducing protein abundance, the mutation weakened the interaction between cMyBP-C and myosin, shifting more myosin molecules into an active structural state capable of generating contraction. The mutation also increased calcium sensitivity, together producing excessive contractile force.
Importantly, these abnormalities arose through a mechanism distinct from the loss-of-protein pathway associated with truncating MYBPC3 mutations.
Despite these divergent disease mechanisms, treatment with mavacamten significantly reduced pathological remodeling in both the R502W mice and animals lacking cMyBP-C. The drug also restored a more normal inactive structural state of myosin in mutant heart muscle and reduced excessive contraction in engineered human heart tissues carrying the same mutation.
“Hence, our data and evidence in the literature suggest that mavacamten is equally effective for carriers of any pathogenic variant in MYH7 or MYBPC3,” the authors conclude. The findings may help explain why genetic differences alone are unlikely to account for the variable clinical responses observed in patients receiving mavacamten.
The work also has implications beyond current therapies. Because some emerging gene therapies aim to replace cMyBP-C rather than correct mutant protein function, the authors suggest those approaches may be less effective for patients carrying missense mutations such as R502W. By contrast, gene-editing strategies capable of directly correcting single-base mutations may prove particularly promising.
The researchers also propose that the newly developed mouse model more closely resembles the relatively mild progression of human hypertrophic cardiomyopathy than previous models based on complete cMyBP-C deficiency, making it a valuable platform for testing future therapies and studying disease biology.
Looking ahead, the investigators suggest that most patients carrying pathogenic MYBPC3 variants could potentially benefit from myosin inhibition regardless of the mutation’s underlying molecular mechanism.
“Our preclinical data indicate that all carriers of pathogenic variants in MYBPC3, arguably the most common cause of HCM, may similarly benefit from myosin inhibition regardless of diverging specific pathomechanisms,” the authors conclude. They add that the limited effectiveness of mavacamten observed in some patients is “probably due to reasons other than the specific HCM variants they carry,” including disease stage, environmental influences, or other genetic factors.
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