Despite positive interim trial results for its experimental gene therapy for spinal muscular atrophy in infants, Novartis announced it will investigate a second trial death that may be related to the same treatment.

The gene therapy, Zolgensma, returned encouraging interim results for 22 babies with Type 1 SMA, the most serious form of spinal muscular atrophy.

An initial death in the trial was found to be unrelated to the treatment, but the second fatality—in a separate European trial—“was deemed possibly related to treatment by the investigator,” the company says.