Roche Holding AG, the Swiss drug giant that said it would pay $4.3 billion in cash to buy Philadelphia-based gene therapy developer Spark Therapeutics in February, has posted another delay.

Roche said Spark agreed to let Roche extend its $114.50 a share cash offer for Spark stock to Oct. 1, after just 24% of the shares were sold on schedule as of Tuesday morning.

The share offer was supposed to expire Sept. 3 at 5 p.m., but has been “extended to provide additional time for the U.S. Federal Trade Commission and the U.K. Competition and Markets Authority to complete their previously disclosed reviews of Roche’s pending acquisition of Spark,” the companies said in a statement.

When the purchase was announced in February, the deal animated the city’s medical-industrial community, and Roche had hoped to close the sale by spring.

But in a sign that investors are resigned to the delays, the stock has been trading below $100, at a discount to the deal price, since the companies in July extended the deal closing deadline into next year, after previous delays. A sale at the planned price would enrich Spark’s owners, which include Wall Street investors, the company’s executives, and the Children’s Hospital of Philadelphia.

Spark shares closed Tuesday at $98.67, up $1.26 (1.29%). Roche shares closed at $34.33, up $0.15 (0.44%).

Roche, through its U.S. subsidiary Genentech, sells Hemlibra, a drug that helps people with hemophilia form blood clots so they don’t easily bleed to death.

Spark is working on a therapy that could cure hemophilia if taken once. Such gene therapy fixes are why Spark’s stock ticker is ONCE.

Antitrust scholar Michael Carrier, of Rutgers University-Camden Law School, has noted that regulators have been puzzling over how traditional drug companies that buy gene therapies, which could make their current drugs obsolete, should best manage conflicts of interest. Such interests could give buyers an incentive to slow development of disease cures.