Roche Holding AG is close to a deal to buy Spark Therapeutics Inc., the Wall Street Journal reported, citing people familiar.

The deal may be valued at almost $5 billion, the newspaper said. Spark had a market capitalization of less than $2 billion on Friday. Roche faces one other bidder for Spark, the newspaper added.

Spark, which specializes on the development of gene therapy drugs, was founded in 2013 at Children’s Hospital of Philadelphia. Four years later, its Luxturna blindness treatment was the first gene therapy for an inherited disease to get U.S. Food and Drug Administration approval.

Spark is also developing gene therapies for hemophilia, which the Swiss drugmaker is seeking to broaden its presence in treating.

Officials from Roche and Spark said they declined to comment on rumors.