Conference Coverage

Duchenne muscular dystrophy gene therapy safe, effective at 4 years



PHOENIX – Children with Duchenne muscular dystrophy (DMD) treated with the only gene therapy to date to be approved for treatment of disease in the United States show sustained maintenance of motor function after 4 years, compared with untreated patients who showed significant decline over the same time period, new research shows.

“Functional assessments demonstrated long-term sustained stabilization of motor function that was clinically meaningful, at ages where functional decline would be expected based on natural history,” the investigators noted in their abstract. Furthermore, the treatment, known as delandistrogene moxeparvovec-rokl (SRP-9001), was well tolerated 4 years post treatment.

The study was presented at the annual meeting of the American Association of Neuromuscular Electrodiagnostic Medicine.

Severe type of DMD

Considered one of the most severe forms of muscular dystrophy, DMD causes progressive muscle wasting stemming from the root genetic cause of missing dystrophin in muscle cells. Often referred to as a molecular “shock absorber,” dystrophin stabilizes the sarcolemma during muscle contractions to prevent degeneration.

SRP-9001, a single-dose recombinant gene therapy administered as an intravenous infusion, was designed to deliver a trimmed down form of dystrophin to compensate for the deficit.

In July, the adeno-associated virus vector (AAV)–based SRP-9001 gene therapy was granted accelerated approval by the Food and Drug Administration for the treatment of ambulatory pediatric patients aged 4-5 years with DMD with a confirmed mutation in the DMD gene.

The therapy is administered over 1-2 hours at a dose of 133 trillion vector genomes per kilogram of body weight.

For Study 101, one of several evaluating the novel therapy, a research team led by senior investigator Jerry Mendell, MD, an attending neurologist at Nationwide Children’s Hospital and professor of pediatrics and neurology at Ohio State University, both in Columbus,evaluated data on four ambulatory male patients aged 4-8 years who received a single IV infusion of the therapy.

All patients also received prednisone 1 mg/kg, 1 day preinfusion and 30 days post infusion.

At 4 years post treatment, there were no new safety events. All treatment-related adverse events occurred mainly within the first 70 days, and all resolved.

The most commonly reported adverse reactions of the gene therapy include vomiting, nausea, increases in liver enzymes, pyrexia (fever), and thrombocytopenia, all of which occurred within 90 days of infusion and been manageable.

Risk mitigation strategies for hepatotoxicity or acute liver injury include pre- and postinfusion monitoring of liver enzymes, the authors noted.

No serious abnormalities were observed in hematologic or chemistry panels, and while three patients had elevated gamma-glutamyl transpeptidase in the first 3 months post treatment, those cases resolved with oral steroid treatment.

Significant improvements in function were observed, with a mean improvement in North Star Ambulatory Assessment (NSAA) scores from baseline of 7.0 points (range, 4-11).

Exploratory analyses further showed that, compared with a propensity score–weighted external control cohort of 21 patients with DMD who did not receive the therapy, those receiving SRP-9001 had a statistically significant difference of 9.4 points in least-squares mean change from baseline to 4 years on the NSAA score (P = .0125).

Similar trends were observed in improvement from baseline in key measures of time to rise, 4-stair climb, and 10- and 100-meter walk/run function tests.

Other reported adverse events include acute serious liver injury, immune-mediated myositis, and myocarditis. Because of the latter risk, the therapy is contraindicated in patients with any deletion in exon 8 and/or exon 9 in the DMD gene.

The current 4-year update on SRP-9001 adds to clinical trial results that have been reported on more than 80 patients treated to date, with favorable results and consistent safety profiles reported at other time points.

Continued FDA approval for the therapy will be contingent upon verification of a clinical benefit in the confirmatory trials, including the EMBARK trial.


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