Swiss pharmaceutical giant Novartis has warned health authorities about the deaths of two children who received Zolgensma, a gene therapy for a rare and often fatal disease for which there were no treatment options until the drug was available, AFP reported.

The two deaths occurred in Russia and Kazakhstan, the Swiss group said in an email to AFP.

Both children died of acute liver failure six weeks after treatment and 1 to 10 days after receiving corticosteroids, which must be administered afterward to reduce side effects, she said.

Novartis notified health authorities in all countries where the treatment is sold about both deaths, including the US Food and Drug Administration (FDA), which first approved it.

Zolgensma is a gene therapy for spinal muscular atrophy, a rare but serious genetic disease that was incurable until a treatment was developed.

Babies affected by this disease rapidly lose motor neurons for important muscle functions such as breathing, swallowing, speech and walking.

Without treatment, their muscles weaken and the disease gradually progresses to paralysis or death, often before the age of two.

This gene therapy has revolutionized the treatment of this degenerative disease, which previously doomed children to premature death. This is directly related to the genetic roots of the disease.

It was first approved in the US in 2019, but its launch was accompanied by many controversies, including over cost.

In the US, Zolgensma cost $2 million at the time of its launch, making it the most expensive treatment in the world.

The cost is due to the complexity of manufacturing the treatment, which involves injecting genetic material into cells to correct defective genes.

Acute liver failure is one of the known potential side effects, the Swiss company said, noting that the risk is already mentioned in warnings detailing the treatment.

However, the company plans to update the information leaflet following the two deaths.

Novartis said it still “strongly believes” in the treatment because of the risks to patients affected by the disease.

Worldwide, Zolgensma has been used to treat more than 2,300 patients since its launch.