(Adds Roche comment on deal completing in first half, reduced percentage of tendered shares, detail about lawsuits)
ZURICH, April 26 (Reuters) - Roche on Friday announced another extension of its $4.3 billion offer for gene therapy specialist Spark Therapeutics, this time until June 3, saying a review by U.S. authorities is taking longer than originally expected.
The Swiss drugmaker said all terms and conditions will remain unchanged during the extended period. Roche earlier this month had extended its offer until May 2, but said the Federal Trade Commission (FTC) needed even more time to complete its review.
"The review of the transaction is ongoing, and the parties are actively working with the government to facilitate that process," Roche said. "In order to provide the government with additional time to complete its current review, Roche has elected to withdraw and refile the premerger notification and report form."
A Roche spokeswoman said the company still expects the deal to be completed in the first half of 2019.
Roche said that as of Thursday, 26.1 percent of Spark's outstanding shares had been tendered in the offer. That is less than the 29.4 percent of Spark shares that had been tendered on April 2, before the Swiss company announced the previous extension of the offer.
Roche said shareholders are free to tender their shares or withdraw them until the offer has closed.
Spark faces several lawsuits in the United States brought by shareholders challenging the sale to Roche, on grounds that it undervalues Spark's stock and is unfair to shareholders. Roche has declined to comment on the lawsuits.
Roche is buying Spark, which has one treatment against blindness on the market and others including for hemophilia A in development, amid an industry-wide push into gene therapy that has also included deals by rivals Novartis and Pfizer . (Reporting by John Miller; Editing by Tassilo Hummel and Richard Pullin)