A pioneering treatment that can reverse a form of childhood vision loss by inserting DNA directly into the eye is on track for regulatory approval in the US, after a panel of scientists endorsed unanimously the “gene therapy” being developed by Spark Therapeutics.

If the US Food and Drug Administration accepts the recommendation of its advisory committee, as it tends to, it would mark the agency’s first approval of such a treatment and herald a new era of medicine where diseases are tackled by inserting functioning copies of genes that are missing or mutated.

Gene therapies seek to tackle illness at its biological source, opening up the possibility of drugs that can be delivered just once rather than on a regular basis. In a reference to the potentially curative properties of such treatments, Spark’s shares are listed on Nasdaq under the ticker ONCE. 

Such therapy also opens up the possibility of finding better treatment options for a string of genetically-driven illnesses that have been hard to tackle with traditional medicine, such as cystic fibrosis and Huntington’s disease.

While representing a huge scientific advance, such one-off treatments are expected to be hugely expensive and threaten to put a strain on already cash-strapped healthcare systems that are structured to pay for chronic therapies. 

Philadelphia-based Spark will not announce a price until after the drug has been approved but analysts and investors expect it to be in excess of $1m, which would make it one of the most expensive therapies of all time.


Expected price of Spark’s gene therapy

The therapy, known as Luxturna, is being developed for a subset of patients with a rare inherited disorder known as Leber congenital amaurosis, who number about 6,000 in the US, Europe and other markets that Spark hopes to enter. People with LCA suffer severe vision loss and are at high risk of going completely blind. 

“The people who are today diagnosed with this disease are essentially told there’s nothing to do about it — go and manage your life or live your life as best you can,” said Jeff Marrazzo, chief executive of Spark in an interview before the advisory committee vote. 

Despite the price tag, analysts do not expect Luxturna to be a big earner for Spark due to the rarity of the disease, with RBC Capital Markets forecasting sales of $120m in 2018. 

Most of Spark’s roughly $3bn market value is ascribed to several gene therapy programmes for haemophilia that are at an earlier stage, which could prove lucrative if successful. Spark is working with Pfizer on one such programme and faces competition from BioMarin, a California-based biotech. 

Shares in Spark, which were suspended for the advisory committee meeting, have added roughly 72 per cent this year, in large part due to successful data from clinical trials of the gene therapies for haemophilia.

Scientists on the advisory committee did not give Spark’s representatives the type of grilling to which other rare disease drugmakers are often subjected, although they did pose several questions.

They discussed whether the treatment really is a one-off or whether it will have to be repeated, with Spark responding by pointing to data showing some patients have kept the full benefit for four years after their first treatment. 

The scientists also discussed the way in which the drug’s effectiveness was measured in clinical trials, with participants being asked to find their way around a mazelike mobility course at different light levels. 

The standard way of measuring vision loss treatments — an eye chart — was less suitable for LCA sufferers because the disease primarily affects light perception and visual field rather than the central eyesight used to read.

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