Just days after releasing positive interim results from its experimental gene therapy Zolgensma for spinal muscular atrophy (SMA), Novartis reported an infant death in a European arm of the study that will be investigated to see if it was treatment related.

SMA is caused by a mutation in the survival motor neuron gene 1 that affects motor nerve cells in the spinal cord, taking away patients’ ability to sit, crawl, or stand, and eventually eat or breathe. It is the primary genetic cause of infant death with most babies dying before the age of two. Zolgensma delivers a functional copy of the gene that encodes the protein SMN that is missing in individuals with SMA.

Novartis spokesperson Eric Althoff emailed Reuters, “Preliminary findings indicate this occurred in the context of a severe respiratory infection followed by neurological complications in a symptomatic SMA Type 1 patient, and was deemed possibly related to treatment by the investigator.”

An autopsy has been performed and results are pending. Investigators and regulatory authorities have been informed. The findings could raise safety concerns for Novartis’ much anticipated gene therapy.

Novartis gained Zolgensma with its acquisition of AveXis in 2018 for $8.7 billion. The company filed for U.S. Food and Drug Administration approval based on a trial of 15 babies with severe SMA, with a decision expected soon.

It also expanded that trial in late 2017 with a new study, STRIVE, that had double the number of patients but a shorter follow-up period. Preliminary results from this study showed an encouraging treatment effect with 21 of 22 patients alive and event-free. One baby died of a respiratory infection unrelated to the treatment. The median age was 9.5 months. The treated patients were compared to natural history of SMA babies, which showed that 50 percent of these infants die or require permanent breathing help by 10.5 months.

Novartis has said that it is negotiating with health plans on price and believes its gene therapy could be cost effective at $4 to $5 million for a one-time treatment. Biogen’s Spinraza for SMA costs $750,000 for the first year and $375,000 in subsequent years.

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