Novartis shares tumbled 10 per cent on Tuesday after the Swiss pharmaceutical group said that a closely watched drug designed to treat a rare muscle-wasting disease had failed a late-stage trial. The drugmaker said its treatment, known as del-desiran, failed to “demonstrate statistically significant improvement” in patients, dealing a fresh blow to the group as it seeks to offset looming patent cliffs in leading drugs. The update is the latest of several setbacks for Novartis, which was revealed last week to have paused trials of an experimental cell therapy in autoimmune diseases in August after three patients died.

It also announced last week that a trial for an experimental cardiovascular drug had failed. Del-desiran is designed to treat people with the genetic muscular condition myotonic dystrophy type 1 (DM1), which has no approved treatment. The promise of the drug helped persuade Novartis to pay $12bn for Avidity Bio Sciences, the US biotech that was developing the drug.

The transaction was Novartis’s biggest acquisition under the tenure of longtime chief executive Vas Narasimhan and part of a spate of dealmaking designed to boost its pipeline. The company has been grappling with the expiration of patents on some of its blockbuster medicines, including top seller Entresto. On Monday Shreeram Aradhye, Novartis’s chief medical officer, said: “Developing therapies for a complex disease like DM1 remains challenging, and setbacks are part of scientific progress.” The company said it would continue to evaluate the full dataset for the drug and engage with health authorities to determine the most appropriate way forward.

Novartis shares are still up about 4 per cent this year.