NEW YORK (Reuters) - The U.S. Food and Drug Administration said on Tuesday that some data from early testing of Novartis’ more than $2 million gene therapy Zolgensma was manipulated, but the agency believes the treatment should remain on the market.

FILE PHOTO: The headquarters of the U.S. Food and Drug Administration (FDA) is shown in Silver Spring, Maryland, November 4, 2009. REUTERS/Jason Reed/File Photo

The FDA said it is carefully assessing the situation.

The manipulated data was used to illustrate comparability between an early version of Zolgensma and the later version of the treatment, which was manufactured using a different process.

The FDA does not believe that the manipulation impacts the safety or testing surrounding the version of the drug, which treats spinal muscular atrophy (SMA), the leading genetic cause of death in infants.

Novartis’ Avexis unit informed the FDA of the data manipulation on June 28, the regulator said.

Novartis acquired the therapy’s maker in 2018, and the drugmaker was aware of the manipulation as early as March - more than two months before the treatment’s approval, the FDA said.

The regulator plans to take action against the company including possible civil or criminal penalties.

In a statement on Tuesday, Novartis said it is “fully confident” in the safety, quality and efficacy of Zolgensma.

The issue is not expected to impact the timing of its ongoing Zolgensma regulatory filings and development programs, the drugmaker added.

“The data in question were a small portion of our overall submission and are limited to an older process no longer in use.”

Zolgensma - the world’s most expensive drug - was approved as a one-time treatment for SMA in late May.

The disease often leads to paralysis, breathing difficulty and death within months for babies born with the most serious Type I form. SMA affects about one in every 10,000 live births, with 50% to 70% having Type I disease.

The FDA said its concerns were currently limited to a small portion of product testing data included in the marketing application for the therapy.

According to an inspection note released by the agency, there were discrepancies in some of its mouse survival data results.

The manipulated data does not change the FDA’s positive assessment of information from human clinical trials, it said. The agency said it will continue to evaluate the integrity of the product testing data used in the development of Zolgensma’s manufacturing process.

U.S.-listed shares of Swiss drugmaker Novartis closed down 2.8% at $88.20 on Tuesday. Shares of Biogen Inc, which makes rival SMA treatment Spinraza, closed up 2.1% at $240.17 and shares of PTC Therapeutics Inc, which is also developing an SMA treatment, closed 4.9% higher at $44.75.