(Bloomberg) -- One of two children who died after being treated with Novartis AG’s Zolgensma was past the US age limit for receiving the gene therapy for spinal muscular atrophy, suggesting the patient was at higher risk for complications. 

The child was 28 months old, Novartis said Friday in an email. That’s within the indication in the country where the child was treated, but past the two-year age cutoff in the US for taking the medicine. The other baby who died was 4 months old, the Swiss drugmaker said. 

The children who died were from Kazakhstan and Russia. Both died of acute liver failure about six weeks after receiving Zolgensma and one to 10 days after tapered doses of a steroid intended to prevent liver complications, Novartis said late Thursday. The cases are the first deaths due to acute liver failure in patients who got the medicine, the company said. 

While the US Food and Drug Administration approved Zolgensma for children under the age of 2 years, European authorities cleared it for those weighing less than 21 kilograms (46 pounds). For children with SMA, that suggests an age of less than 5 years, Novartis said. There is no age limit for treatment in Russia, the company said. 

In the US and other countries where newborn babies are screened for the disease, Zolgensma is dosed as early as possible, ideally a few weeks after birth and before symptoms become apparent. However, as families and governments elsewhere in the world begin to get access to the $2.1 million drug, children are being treated who are much older and sicker. 

First approved in the US in 2019, Zolgensma is part of a wave of new treatments that have transformed the prognosis for children with SMA, a muscle-wasting disease that robs babies of the ability to move, swallow and breathe. If left untreated, the most serious form of the disease is usually fatal by age 2. 

However, the gene therapy comes with a risk of immune reactions and can be toxic to the liver. Research has shown that the risk may be higher for children who are older, weigh more and require a larger dose of the therapy. 

Novartis’s original studies of the drug treated children up to the age of eight months. 

The shares fell 1.2% in Zurich. 


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