The cause of a type of hereditary blindness has been traced to a genetic mutation, a discovery that potentially opens a new treatment approach, Canadian and international researchers say.

The inherited eye disease, called Leber congenital amaurosis, usually shows its first signs at birth or in the months following. It affects about one in 80,000 newborns. About 1,000 Canadians live with the effects.

Scientists at Montreal's McGill University and their co-authors have identified that a gene called NMNAT1 can cause LCA.

"We're getting closer to finding 100 per cent of the genes causing Leber congenital amaurosis," said Dr. Robert Koenekoop, director of the McGill Ocular Genetics Laboratory, who led the research team. "That gives an immediate relief to the families, because it confirms the diagnosis [and] gives you a treatment avenue."

Koenekoop said that from his clinical experience, confirming the diagnosis of LCA allays parents' concerns about the condition being something in the brain.

The researchers' genetic discovery helps provide families with a firm diagnosis, Robert Koenenkoop says. (CBC)

The disease was considered untreatable 15 years ago, but that is no longer the case for some subtypes, Koenekoop said.

For the study in this week's issue of Nature Genetics, scientists analyzed the genomes of 60 infants with LCA of unknown cause.

They discovered a mutation on the NMNAT1 gene, which is found in all human cells. It produces a coenzyme called NAD that is involved in hundreds of reactions.

In animal experiments, using the enzyme as a drug rescued some neurons, researchers found.

It's estimated that NMNAT1 is responsible for about 10 per cent of cases of LCA.

Seeing the sky

The new findings suggest that NMNAT1 acts to protect photoreceptor cells in the retina from degeneration in response to damage or stress.

Dale Turner of Toronto grew up with limited central vision from LCA until an experimental gene therapy surgery four years ago restored much of his vision.

"On the third day, I peeled back the patch and I was able to see things like never before," Turner recalled. "The sky was the most blue I'd ever seen it. I couldn't really see colours before the gene therapy procedure and I could after. I think that just represents so much hope."

Recovering vision

Turner's experience has already helped doctors learn to recruit patients and design a clinical trial, which could speed up the next round of research, Koenekoop said.

So far, doctors may be able to give parents an idea of the severity of the disease based on the results of genetic testing.

Koenekoop cautioned against calling the gene therapy and drug treatments a cure.

"We know some cells are dead," he noted in an interview with CBC Radio's As It Happens. "What we're happy to tell you is we're recovering vision."

The other authors of the study were from Houston; Chicago; Cleveland; London; Lahore, Pakistan; Shanghai; and Leeds, U.K., while steering committee members came from Ottawa, Vancouver, Calgary, Toronto and St. John's.

The research was funded by the Foundation Fighting Blindness Canada, Finding of Rare Disease Genes in Canada (FORGE Canada), Genome Canada, the Canadian Institutes of Health Research, Ontario Genomics Institute, Genome Quebec and Genome British Columbia.

With files from CBC's Salimah Shivji