TRENTON, N.J. (AP) — U.S. regulators want to know why Novartis didn’t disclose a problem with testing data until after the Swiss drugmaker’s $2.1 million gene therapy was approved.

Food and Drug Administration
said the manipulated data involves testing of the therapy on animals, not on patients. The FDA on Tuesday said it’s confident the drug should remain on the market. The agency said it will consider criminal or civil penalties if appropriate.

Zolgensma, the most expensive treatment ever, was approved in May. It’s expected to be a one-time treatment for a rare inherited condition, spinal muscular atrophy. It was approved for children under 2.

Novartis had no immediate comment.