Novartis has not yet said whether it will keep developing del-desiran, its drug for myotonic dystrophy type 1 (DM1). The del-desiran next steps depend on the full HARBOR dataset and on talks with regulators. On 27 October 2026, Novartis reported a USD 1.9 billion partial impairment on the asset. It first reported that the phase 3 trial missed its primary endpoint on 8 September 2026.
This article sets out what Novartis has disclosed, what its accounts show and what would settle the question. It relies on Novartis documents first. Trade reporting is named in the text where it is used.
Del-Desiran Next Steps: What Novartis Has Said So Far
In its 8 September 2026 release, Novartis said it was evaluating the full HARBOR dataset. It said it would engage health authorities on the development path.
Shreeram Aradhye, President, Development and Chief Medical Officer, Novartis, said there are still no approved DM1 treatments. He added that “setbacks are part of scientific progress.” Both statements come from the company release.
Novartis repeated its position in its third-quarter interim report, filed on 27 October 2026. The report lists del-desiran in phase 3, with a first planned submission of 2029 or later. It says Novartis expects to engage health authorities on the development path.
In the 27 October media release, chief executive Vas Narasimhan said the del-desiran readout “was not what we had hoped.” He said the data showed evidence of clinical activity and that Novartis is working through the development path.
A reading of both documents on 28 October 2026 found no new trial, termination or filing plan announced. That is a dated search finding, not proof that no decision exists.
What HARBOR Showed and Did Not Show
HARBOR (NCT06411288) was a global, randomised, double-blind, placebo-controlled phase 3 study. It enrolled about 150 people with DM1. Participants received del-desiran or placebo every eight weeks over 54 weeks.
The primary endpoint was video hand opening time (vHOT), a measure of hand myotonia. According to Novartis, del-desiran did not show a statistically significant improvement over placebo.
Novartis also reported “evidence of clinical activity” in secondary endpoints and exploratory analyses. The release does not say which endpoints, and it gives no numbers. Its listed key secondary endpoints were hand grip strength, quantitative muscle testing, DM1-Activ and the 10-metre walk/run test.
Novartis described safety findings as “generally consistent with previously reported data.” The release gives no HARBOR safety figures, so that statement cannot yet be checked.
The designations the asset already holds
Novartis lists FDA Orphan Drug, Fast Track and Breakthrough Therapy designations for del-desiran. It also lists an EU orphan medicinal product designation. These designations support dialogue with regulators. They are not approvals, and no regulator has been reported as accepting a filing.
What Earlier Data Suggested
The phase 1/2 MARINA study came first. NeurologyLive reported that muscle biopsies showed dose-dependent delivery of the siRNA and reduced DMPK mRNA. It also reported a 3.84-point rise in the muscle testing score at day 183 for 4 mg/kg. The placebo group fell 1.01 points.
The same report notes that the safety population was 38 participants. That size limits conclusions on function. It also notes a partial FDA clinical hold, placed in 2022 and removed in October 2024. Avidity said in September 2022 that one participant in the 4 mg/kg cohort had a serious adverse event.
Those early signals did not carry through to the primary endpoint in HARBOR. Novartis has not explained why. Only the full dataset can show whether the gap lies in the drug, the endpoint or the trial design. That answer will shape the del-desiran next steps.
How the USD 1.9 Billion Impairment Changes the Picture
Novartis took the charge against acquired in-process research and development. Its 27 October 2026 media release said third-quarter operating income fell 59 per cent in US dollar terms. It attributed the fall mainly to higher R&D expenses, including a USD 1.9 billion partial impairment of the del-desiran asset.
The interim report puts the charge at USD 1.94 billion, recognised in September. It says the charge reduced the asset’s carrying amount to USD 5.5 billion.
A partial charge is not a write-off. Novartis still carries del-desiran at a substantial value. The report adds a general warning that impairment testing “may lead to potentially significant impairment charges in the future.”
The documents do not publish the valuation assumptions behind the charge. They do not say how much the timeline or the probability of success moved. Readers should treat any such split as unconfirmed. The charge is an accounting judgement. It does not fix the del-desiran next steps.
Novartis paid USD 72 per share in cash for Avidity Biosciences. The earlier report on the Avidity deal set out the original terms. Total consideration was about USD 12.0 billion on a fully diluted basis. The acquisition completed on 27 February 2026.
Market and Analyst Reaction
Novartis shares fell 11 per cent on the SIX Swiss Exchange on 8 September, according to GEN. GEN put the move at CHF 125.46 to CHF 111.80.
GEN also reported individual analyst views on the del-desiran next steps. A Guggenheim analyst cut a risk-adjusted 2033 sales forecast for del-desiran by 45 per cent. The new figure is USD 960 million, from USD 1.76 billion. A Vontobel analyst removed a USD 3 billion peak sales projection. These are single-analyst estimates and are not verified.
A Bellevue Asset Management investor noted that Avidity designed HARBOR before Novartis bought the company. A William Blair analyst said the miss leaves open space in DM1. The analyst pointed to VX-670, from Vertex and Entrada, as a strong competitor. Each point rests on that one GEN report.
The September release kept Novartis’s 5 to 6 per cent compound annual sales growth guidance for 2025 to 2030. In the 27 October report, net sales guidance for 2026 was unchanged at low single-digit growth.
What Happens to the Rest of the Avidity Portfolio
HARBOR concerns only one of the three neuromuscular assets Novartis gained with Avidity. The other two sit in separate programmes with their own data and timelines.
Del-zota in Duchenne muscular dystrophy
Novartis said the FDA granted priority review for del-zota (delpacibart zotadirsen). A community letter dated 8 September says the FDA accepted the biologics licence application for review. It adds that the application will be assessed under the accelerated approval pathway. The application covers people with Duchenne muscular dystrophy whose variant can be treated by exon 44 skipping.
The application draws on the phase 1/2 EXPLORE44 study and its open-label extension. The phase 3 SAFARI44 study is the confirmatory trial and runs outside the United States. The letter states no PDUFA goal date. Other pending FDA actions appear in the FDA drug approval decisions tracker.
Del-brax in facioscapulohumeral muscular dystrophy
The interim report lists del-brax (delpacibart braxlosiran) in phase 3, with a first planned submission in 2028. Novartis plans an FDA meeting in the fourth quarter. It cites positive phase 1/2 biomarker data as the basis.
When Will the Del-Desiran Next Steps Become Clear?
Three events would answer the question. First, Novartis would need to publish the full HARBOR data, including the secondary endpoints. Second, regulators would need to say what evidence they would accept. Third, Novartis would need to announce, or decline to announce, a new trial.
The documents read give no dates for any of the three. Until then the answer is open. The asset is carried at USD 5.5 billion, and its first filing is listed as 2029 or later.
For UK and EU readers, the picture is early. Novartis lists an EU orphan designation. The same reading of its 8 September and 27 October documents found no UK or EU filing announcement.
For people with DM1, the wait continues. Novartis says no approved treatment exists. The del-desiran next steps will show whether this programme stays among the contenders.
