Roche Holding is to buy US-based Spark Therapeutics in a $4.3 billion deal that will give the Swiss drugmaker a foothold in gene therapy. 

Roche will pay $114.50 per share for Spark, more than twice the US company closing price on February 22, the Swiss company said today. 

Basel-based Roche is buying Spark and its portfolio of treatments for blindness, haemophilia and neurodegenerative diseases, among other conditions, as rivals including Novartis, also move aggressively into gene therapy. 

"Spark Therapeutics' proven expertise in the entire gene therapy value chain may offer important new opportunities for the treatment of serious diseases," Roche's chief executive Severin Schwan said. 

Schwan is counting on new medicines, including gene therapies, to help compensate for patent losses on his $21-billion-per-year trio of cancer medicines Rituxan, Herceptin and Avastin, that are facing competition from cheaper copies. 

Roche, the biggest cancer drugs maker, was late to the game in immuno-oncology where Merck's Keytruda is becoming the dominant player and has eclipsed Roche's own product, Tecentriq, that seeks to harness the body's immune system to fight cancer.

Analysts said the Spark deal would give Roche a proven platform for getting gene therapies to market, but did not come without risks – including getting beaten to market by rivals with similar treatments in the works.

Gene therapies use specially engineered viruses, or viral vectors, to deliver genetic material into defective cells, in hopes of improving or potentially even curing an inherited condition. 

Spark has an approved gene therapy treatment Luxturna, which is sold in the US by Spark and elsewhere by Novartis after its approval in 2017. 

Luxturna targets a rare genetic disease, Leber's congenital amaurosis, that causes blindness in about one in 200,000 people. 

Loss-making Spark had $51.6m in revenue in the first nine months of 2018 from Luxturna and also had income from a deal with Pfizer, which it is partnering on another gene therapy for haemophilia B. 

Roche's Spark deal follows Novartis's $8.7 billion purchase of US-based Avexis last year, also to gain a platform of gene therapies for disorders including spinal muscular atrophy.

Novartis has made gene therapy one of its focus areas, giving it a head start on Roche. US approval of Novartis's SMA medicine is slated for coming months.

Among Spark's top drug hopefuls is SPK-8011, for haemophilia A, expected to start Phase 3 trials in 2019. It is also working on treatments for Pompe disease, blindness-causing choroideremia and Huntington's disease.

Roche already sells Hemlibra against haemophilia A that helps stop bleeding in patients with the life-threatening genetic disorder that prevents their blood from clotting.

Hemlibra, approved in 2017, had 224 million Swiss francs ($224.18 million) in sales last year. 

With Spark, Roche enters a crowded haemophilia gene therapy market that could become a big competitor to Hemlibra, as other players – Biomarin Pharma, Uniqure and Sangamo Therapeutics – also have gene therapies in the works.