A major data-manipulation scandal has rocked Novartis. Here's everything we learned from a new 59-page letter the Swiss drug giant sent to its regulators.

• A data-manipulation scandal has rocked Swiss drug giant Novartis and its new rare-disease treatment Zolgensma.
• A clearer picture is now emerging with a new 59-page letter Novartis's AveXis unit sent to the FDA.
• AveXis learned in March of an allegation that two senior executives led data manipulation at the company, according to the letter. The company said it initially led a secret investigation to make sure evidence would be preserved "without interference."
• "Moreover, the investigation was significantly drawn out due to the implicated senior executives' lack of cooperation and categorical denial of the allegations, which continues to this day," the letter says.
• A representative for Brian Kaspar said that Kaspar had cooperated with the company investigation and denied any wrongdoing. Allan Kaspar did not immediately return Business Insider's request for comment.
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Scandal has rocked the Swiss drug giant Novartis since the US Food and Drug Administration revealed last month that the company submitted manipulated data on a key drug to the regulator.

Novartis would later blame Brian and Allan Kaspar, brothers who were top execs at its AveXis unit, for the problems. Now, more allegations about the Kaspars are emerging in a 59-page letter from Novartis's AveXis to the FDA, showing a clearer picture of how events unfolded earlier this year.

The letter was part of a response to the FDA after an FDA inspection found potential violations at AveXis's San Diego laboratory. It includes the allegation that the two execs led the data manipulation in question, and that their non-cooperation and denials delayed AveXis's investigation into the matter.

"Such conduct is unacceptable, and the two AveXis senior exeuctives have been terminated," the letter said.

The manipulated data was used to secure approval for Zolgensma, a treatment for spinal muscular atrophy. FDA has said Zolgensma should remain on the market.

Read more: 'Like we were being forced to gamble with our son's life': Health insurers won't pay for a $2.1 million drug for kids, and parents say they're running out of time

A representative for Brian Kaspar said that he had cooperated with the company investigation and denied any wrongdoing, while Allan Kaspar did not immediately return Business Insider's request for comment. The FDA has said it could impose civil or criminal penalties.

The manipulated data was part of a large packet submitted to the FDA and reviewed as part of the drug's approval. The particular issue pertained to data from product testing done in mice, according to the letter and a press release from the FDA last month.

In addition to the conduct itself, the timeline has also come under scrutiny, since Novartis had knowledge of potential data manipulation issues before Zolgensma was approved in May - and only disclosed the problem the next month, in June.

Read more: Elizabeth Warren and Bernie Sanders just slammed the Swiss drug giant Novartis over a new controversy swirling around the world's most expensive drug

Here's what else we just learned from the letter:

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