he Food and Drug Administration has halted a clinical trial of Novartis’ Zolgensma gene therapy due to a safety concern found in an animal study, the company said Wednesday.

The hold affects the Novartis (NVS) clinical trial known as STRONG, which was testing a higher dose of Zolgensma administered by spinal injection to older children with spinal muscular atrophy (SMA). It does not affect the already approved treatment of infants and children.

Novartis said its subsidiary AveXis informed regulators about findings from an animal study that showed “dorsal root ganglia (DRG) mononuclear cell inflammation, sometimes accompanied by neuronal cell body degeneration or loss.” The clinical significance of this adverse safety signal is not known, but it can be associated with “sensory effects,” the company added.

Halting the STRONG clinical trial is a setback for Novartis’ effort to expand the use of Zolgensma to older patients with SMA. Biogen’s Spinraza treatment is already approved for older SMA patients. Roche (RHHBY) is expected to secure approval of its own SMA treatment next year.

Novartis said it has seen no reports of “sensory effects” in patients and is working with the FDA to resolve safety concerns and resume dosing of Zolgensma in the clinical trial.

The FDA’s action on Wednesday follows a controversy involving manipulation of data used to support Zolgensma’s approval. In an unusual rebuke, the agency said in August that AveXis knew that preclinical data had been falsified before the drug was approved in May, but did not inform the agency until later. The agency said that the drug should stay on the market, but the scandal sparked anger from lawmakers and a pledge from Novartis’s CEO, Vas Narasimhan, to move more quickly on disclosing issues around data integrity.

Zolgensma carries a price tag of $2.1 million, making it the world’s most expensive medicine. Earlier this month, Novartis said the gene therapy had been used to treat 100 patients since its launch and brought in $160 million in the third quarter, beating analysts’ expectations.

Source STAT