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home / 世界杯决赛2022

‘each gene tells a story’: discovery around childhood blindness made in montreal

"this piece of the puzzle turns out to be a huge development: a gene in the retina that controls other genes."

by susan schwartz

oct 14 2022
read time 4 minute read
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three outaouais brothers with progressive vision loss caused by a disease known as retinitis pigmentosa — jonathan, sébastien and christopher varin — and a multi-year collaboration between the montreal children’s hospital and the institut de recherches cliniques de montréal (ircm) have contributed to a major discovery about one of the most common causes of childhood blindness.

a promising discovery published recently in the journal science advances  shows that mutations in the gene known as bcor cause early-onset retinitis pigmentosa.

“every gene discovery is a time to celebrate because it is a piece of the puzzle,” dr. robert k. koenekoop, director of pediatric ophthalmology at the montreal children’s hospital, told the montreal gazette. “this piece of the puzzle turns out to be a huge development: a gene in the retina that controls other genes.”
the research described in the study, published in september, was conducted in the ircm laboratory of dr. michel cayouette, a professor in the department of medicine at the université de montréal, with postdoctoral fellow maéva langouët and research professional christine jolicoeur, in close collaboration with koenekoop.

october is blindness awareness month and the second thursday of the month is world sight day , an annual global event intended to bring attention to blindness and vision impairment.

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retinitis pigmentosa (rp), often diagnosed in childhood or adolescence, is a group of inherited diseases causing degeneration of the retina — the thin layer of nervous tissue at the back of the eye is crucial for vision — and the progressive loss of night and peripheral vision. one of the most common inherited diseases of the retina, it affects one in 3,500 to 4,000 canadians. although the rate of progression and extent of vision loss varies from person to person, many with rp are legally blind by age 40.
rp was first described in the 19th century but poorly understood until fairly recently, said koenekoop, a senior scientist in the child health and human development program at the research institute of the mcgill university health centre. “now, with genetic advances, we know that each gene tells a story: it identifies pathways and therapeutic options.”
in the 27 years he has worked in the field, “we have gone from saying, ‘you have retinitis pigmentosa: there is nothing we can do’ to ‘you have retinitis pigmentosa: let’s find the gene. gene therapy is coming. hang in there,'” said koenekoop, who sees 10 to 15 young patients with the condition each week in the low-vision clinic he runs at the montreal children’s.
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he immediately does genetic testing to determine whether the young patient has a mutation in one of the 200 known genes involved in rp. “in the past few years, we discovered that, in 60 to 70 per cent of cases, we can find the gene,” he said. “and when you find the gene, it helps the child immediately for planning school and jobs.
“there is genetic counselling and the excitement of telling patients about trials and studies,” he said. “i give antioxidants and talk about acupuncture.” acupuncture is believed to increase blood flow to the retina, said koenekoop. “definitely it improves visual field.
“we try to slow the disease and to stop it completely and then we try to improve the vision. what we have seen most is visual improvement: it is harder to stop or slow the retinal degeneration process unless we catch it early,” he said.
most important, koenekoop said, is that “we are entering an era of personalized medicine. some of these genes are being replaced in the eye — and children are starting to see.”
a form of specific gene therapy for children with certain type of retinitis pigmentosa, for instance, was approved only weeks ago by the régie de l’assurance maladie du québec.
successful clinical trials are underway for five or six major genes and the hope is that they will be approved in the next several years, he said. “this will mean that 20 per cent of patients with retinitis pigmentosa can be treated.”

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koenekoop first saw the varin brothers more than 15 years ago, when they were children. he checked all 200 genes known to be involved in retinal degeneration and found nothing. but a genome scan turned up something: all three boys had the same mutation of the bcor gene. bcor is involved in the development of certain forms of cancer, but they did not have cancer.
“we said: ‘this could be a new mechanism into how the retina functions and develops.'” koenekoop recalled. he invited cayouette, who is recognized internationally for his work on the biology of the retina, to join him.

“similar to a thermostat regulating the temperature in a house, we discovered that bcor precisely regulates the level of expression of many retinal genes,” cayouette said. “when genetic errors appear in bcor, this regulation process is altered, leading to abnormal activity that eventually causes retinal cell death and vision loss. “

the discovery will have broad implications in changing the gene therapy landscape, he said. “who would have thought of a cancer gene used in the retina for retinal development? it is the same gene — with a different function than in the bone marrow.”
the next step, cayouette said, is to manipulate the expression of these genes, using animal models to create the same mutation as the one identified in the varin brothers.

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meanwhile the brothers — jonathan, 25; sébastien, 23; and christopher, 17 — are doing well. jonathan and sébastien have their driver’s licences, sébastien hopes to become a video game developer, and christopher wants to be a nurse: he knows the future could hold challenges but, for now, “i feel like my vision is still pretty normal.”
“it’s cool that they have found the gene, because it will make research go further. i am optimistic.”
sschwartz@postmedia.com
susan schwartz, montreal gazette
susan schwartz, montreal gazette

we used typewriters when i started at the gazette, and big black rotary phones. nearly everyone smoked. today’s newsroom looks different but the work – reporting and informing my readers – remains constant and rewarding. i am grateful to my adviser at mcgill, where i was a neurobiology major, for steering me to journalism. undoubtedly, he realized i wasn’t cut out for neurobiology.

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