UPDATED: A gene therapy 'cure' for blindness starts to fade within a few years

The two key reasons why gene therapies command such avid attention these days center on their promise of providing a cure for some terrible conditions along with the prospect of a 7-figure price tag. But some prominent investigators at the University of Pennsylvania raised a cautionary note over the weekend, reporting that their "cure" for blindness only worked for one to three years before patients' vision began to fade again. And their decline clearly rattled investors' faith in a hot biotech player involved in the same field.

UPenn's Samuel Jacobson

The team, led by Samuel Jacobson, followed up on the experiences of three long-term patients who had received a gene therapy that uses a virus to deliver instructions to the eye to begin producing healthy copies of the RPE65 gene needed to spur production of a vital protein. Mutations in the gene are linked to about 10% of all cases of Leber congenital amaurosis (LCA), an inherited disease.

A number of patients in the group of 15 in the study demonstrated rapid improvement in vision, including the three long-term patients studied in the follow-up. This was one of several small human studies that helped revive expectations for gene therapies. But instead of the permanent cure everyone was hoping for, their vision peaked and then began to decline.

"Our earlier results and these new measurements showed that photoreceptors continued to die at the same rate as they do in the natural course of the disease, regardless of treatment," said Jacobson in a statement.

But the setback doesn't spell the end of their work. Jacobson concluded that a follow-up treatment could be used to maintain vision, combination therapies could be developed to amp up efficacy and patients could be evaluated to determine which would most likely benefit the most from these therapies.

Spark Therapeutics' ($ONCE) lead therapy delivers a functional copy of the RPE65 gene for LCA patients. The treatment is currently in a Phase III study with 28 patients. And to be fair to the biotechs in this first wave of developers, the limitations of Penn's treatment could be limited to the disease or the particular technology it uses to reintroduce the RPE65 gene.

Shares for Spark plunged 16% in early trading on Monday, wiping out about $200 million in value. But the company put up a vigorous defense of their drug, noting differences between its program and the one faltering at Penn, and saw their losses pared to 6.5% by mid-afternoon.

Those are all important considerations as analysts and insiders in this field speculate how payers could afford gene therapies that may come with a price tag of $1 million or more. Figuring out how to price a therapy with no guarantee of a cure can only complicate matters.

- here's the release