Heart-related side effects from gene therapy were uncommon, typically mild and concentrated in the first few weeks after treatment in Duchenne muscular dystrophy (DMD) and related neuromuscular diseases, according to a large analysis published recently in Circulation: Heart Failure.
For patients considering these therapies, these findings suggest that risks can be managed with close monitoring and early care. Researchers reviewed 80 studies involving 1,939 patients who received adeno-associated virus gene-replacement therapy, a leading experimental and approved approach for conditions such as DMD.
Over 2,122 patient-years of follow-up, 734 adverse events were reported, including 71 cases of heart injury. That translates to about 8.6 events per 100 patient-years, or roughly 6% of treated patients.
Importantly for people living with DMD, nearly all heart-related events occurred shortly after treatment. Myocardial injury peaked in the first week, while myocarditis (inflammation of the heart muscle) most often appeared in the second and third weeks. No cases were reported after the first month. This predictable timing gives clinicians a clear window to monitor patients closely and respond quickly if needed.
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“These findings have clear operational implications: early, protocolized cardiac surveillance (troponin/ECG and prompt imaging) during the first month after dosing and pretrial stratification by dose, vector platform, and indication,” explained the authors of this analysis.
Most cases did not lead to serious problems. About 87% of patients with myocarditis or heart injury had no meaningful clinical impact. Only eight patients, or 12%, developed temporary weakening of the heart’s pumping function, and all recovered during follow-up. One death was reported, but it was linked to a severe immune reaction causing capillary leak syndrome rather than myocarditis alone.
The analysis also found that risk was tied to higher doses, specifically intravenous doses greater than 1×10¹³ vector genomes per kilogram of body weight. Events were seen mainly in neuromuscular diseases such as DMD, spinal muscular atrophy and X-linked myotubular myopathy. Certain viral vectors, including recombinant adeno-associated viruses and serotypes 8 and 9, were more often associated with these effects.
For patients with DMD, the findings suggest that gene therapy remains promising but requires careful planning. Doctors are advised to use cautious dosing and provide intensive heart monitoring during the first month, including blood tests and heart imaging when needed. Because most cases are mild and respond to treatments such as steroids, early detection can prevent complications while avoiding unnecessary alarm.
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