Gene therapy for Duchenne gives modest gains and real risks, a review finds

An independent meta-analysis of gene therapy for Duchenne muscular dystrophy concluded that the treatments deliver only modest functional gains — concentrated in the youngest boys and, against control groups, largely unproven — while carrying serious risks that in rare cases have been fatal [s1]. The finding tempers the marketing around a class of one-time therapies that cost millions of dollars per dose and were approved on limited evidence [s1].

Duchenne muscular dystrophy is a fatal genetic disease, almost always in boys, caused by mutations that abolish dystrophin, a protein muscles need to withstand contraction [s1]. AAV-based mini- and micro-dystrophin therapies use a harmless virus to deliver a shortened, working version of the gene, in the hope of slowing the relentless loss of muscle [s1]. The lead product, delandistrogene moxeparvovec (Sarepta's Elevidys), reached the US market before a randomised trial had shown it worked on its primary measure — which is precisely why an independent synthesis of the trial data matters.

What the meta-analysis found

The review, published in the Journal of Medical Genetics, followed PRISMA methodology, searched five databases through November 2025 and was prospectively registered [s1]. It identified nine studies (six trials, 218 patients), with four contributing to the pooled analysis [s1].

The efficacy picture is mixed. Delandistrogene moxeparvovec improved the North Star Ambulatory Assessment (NSAA), a standard motor-function score, by 3.08 points at one year (95% CI 1.85 to 4.32) — but that gain was measured mostly against each child's own baseline, not against a control group [s1]. The benefit skewed strongly by age: 4.06 points in 4-to-5-year-olds against just 1.01 points in 6-to-7-year-olds [s1]. When the analysis compared treated boys with control groups, the only statistically significant improvement was in time to rise from the floor (0.64 seconds faster); there was no significant difference in NSAA or in the other timed tests [s1]. A second product, fordadistrogene movaparvovec, showed smaller effects [s1]. The authors' conclusion is deliberately plain: AAV gene therapies "provide modest functional benefits in ambulatory boys with DMD, particularly at younger ages, but carry important safety risks" [s1].

On safety, most patients had treatment-related adverse events, generally mild and transient, but serious events occurred — including liver toxicity and, rarely, fatal outcomes [s1].

What the manufacturer's trial claims

The pivotal trial behind the lead product, EMBARK, illustrates the gap between an approval and a clear result. EMBARK randomised 125 ambulatory boys aged 4 to under 8 to a single intravenous dose or placebo, and — as Sarepta's own two-year report states — its primary endpoint, the change in NSAA at 52 weeks versus placebo, did not reach statistical significance [s2]. The company nonetheless reports that at two years, treated boys did significantly better than a matched external control group on NSAA, time to rise and the 10-metre walk/run, which it frames as sustained slowing of the disease [s2].

That two-year claim should be read as what it is: a manufacturer analysis against a propensity-weighted external control rather than the trial's own randomised placebo group [s2]. External-control comparisons are more vulnerable to bias than a randomised comparison, and they are the kind of secondary analysis that can make a drug that missed its primary endpoint look effective. The independent meta-analysis, pooling the randomised evidence, is the more conservative and more trustworthy read [s1].

Why it matters

Families facing Duchenne confront an agonising decision about a one-time, irreversible and extremely expensive therapy, and they deserve the unhyped version: the benefit is real but small, clearest in the youngest and least-progressed patients, and weakly supported when weighed against proper controls — and the risks are serious enough to include death [s1][s2]. Reports of fatal liver failure after Duchenne gene therapy have already prompted regulatory scrutiny, which is consistent with the "rare fatal outcomes" the meta-analysis records [s1]. Health Newspapers has examined the wider AAV gene-therapy field, including an AAV9 gene therapy trial in the fatal childhood disease GM1 gangliosidosis and how the FDA is loosening manufacturing rules for cell and gene therapies.

What to watch

The evidence gap the reviewers flag — larger trials with longer follow-up and randomised comparators — is what would settle whether these therapies change the disease's course or merely nudge a score [s1]. Age-restricted labelling and the durability of any benefit past two years are the practical questions for regulators and clinicians [s1][s2].

This article describes research and regulatory status and is not medical advice or a treatment recommendation.

Sources

• Safety and efficacy of AAV-based mini- and micro-dystrophin gene therapies in Duchenne muscular dystrophy: a systematic review and meta-analysis — Journal of Medical Genetics, 16 September 2026
• Two-year outcomes following delandistrogene moxeparvovec treatment in ambulatory patients with Duchenne muscular dystrophy: phase 3 EMBARK trial — Neurology and Therapy, 10 January 2026