MDA 2023: Exondys 51 may boost survival for DMD patients

Longest survival times seen among patients on earlier, longer treatment

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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People with Duchenne muscular dystrophy (DMD) who are treated with Exondys 51 (eteplirsen) live significantly longer than would be expected without the treatment, by a median of more than five years, according to a new analysis.

The longest survival times were generally seen among patients who started on therapy early and were treated for many years.

Findings were presented this month at the MDA Clinical & Scientific Conference, in the poster “Survival in Eteplirsen-Treated vs Duchenne Muscular Dystrophy Natural History Patients: An Indirect Treatment Comparison Using Real-World Data.” The work was funded by Sarepta Therapeutics, which markets Exondys 51.

“These real-world data suggest that [Exondys 51] may prolong survival in patients with DMD across a wide age range,” researchers wrote in their abstract.

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Exondys 51 is an approved therapy that targets about 13% of DMD patients

Exondys 51 is an exon-skipping therapy that is approved in the U.S. to treat people with DMD caused by mutations amenable to exon 51 skipping (about 13% of DMD patients). The therapy is designed to mask a small sequence in the DMD gene when the gene is “read” to make protein, allowing cells to produce a shorter but functional version of the dystrophin protein.

Sarepta runs a program called SareptAssist, which provides support for patients who are treated with Exondys 51. According to the company, the program covers most insured patients who have mutations amenable to exon 51 skipping.

In the MDA poster, scientists at Sarepta and other institutions analyzed data for 579 DMD patients collected as part of SareptAssist. The patients started treatment at a mean age of 11.9 years, and the mean duration of treatment was 3.7 years at the time of the analysis.

These real-world data suggest that [Exondys 51] may prolong survival in patients with DMD across a wide age range.

Outcomes from these treated patients were compared with historical data (collected from the published scientific literature) for 1,224 patients with DMD who had mutations amenable to exon 51 skipping but were not treated with Exondys 51.

In statistical models, the scientists found that the odds of survival were significantly higher, by about 66%, in patients treated with Exondys 51 compared to the controls. Median survival time was more than five years longer in Exondys 51-treated patients.

“Real-world data from patients treated with [Exondys 51] had significantly longer survival compared with reproduced patient-level data from DMD [natural history] controls, with a median difference of at least 5.4 years,” the researchers wrote.

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Earlier treatment linked to longer survival times

Further examination of the data suggested that patients who start on Exondys 51 at a younger age tended to live longer than those who didn’t start on treatment until later.

Analyses also showed that better survival outcomes were only seen among patients who were on Exondys 51 for at least a few years: for patients on the therapy less than two years, survival outcomes were comparable to the historical controls, with a median survival age in the late 20s in both groups.

A notable limitation of this analysis, the researchers stated, is that data on prognostic factors — such as other treatment patterns, measures of health upon starting treatment, and type of disease-causing mutation — were not available, and differences between the groups may have influenced the findings.

The researchers also noted that, although nearly half of the patients have been on Exondys 51 for at least four years, this is still a relatively short treatment duration to discern survival benefits.

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