Better options for treating birdshot

27 October 16

written by:

Ade Deane-Pratt

(more articles)

New research funding partnership between Fight for Sight and Birdshot Uveitis Society

Birdshot uveitis is a rare autoimmune disorder that has the potential to blind. It’s notoriously hard to treat. We are partnering with Birdshot Uveitis Society to try to change that with new grants to researchers in London and Birmingham, to fund pioneering research that could lead to better treatments.

Cartoon diagram of the eye with 3 views: 1) The eyeball in profile showing that the retina is at the back of the eye. 2) A front view showing a healthy retina that is evenly coloured reddish-orange. 3) A retina showing features of birdshot, with scattered dots of a lighter yellowish-white colour. This pattern gives birdshot its name.

In birdshot, which is strongly linked to the gene HLA-A29, the immune system attacks two critical structures at the back of the eye: the retina and the choroid. The retina contains the photoreceptor cells that detect light and send visual signals to the brain, while the choroid is a layer of blood vessels that supplies the retina with oxygen and nutrition. When this supply is interrupted as during an inflammatory immune response, the photoreceptors can’t function normally.

Current options for treatment are limited to steroids and drugs to suppress the immune system. However in the long term these can cause sight-threatening complications such as cataract and glaucoma. We need some better options.

Stem cells from patients

Dr Anai Gonzalez Cordero at UCL Institute of Ophthalmology is leading one of the two new studies. The team will study a layer of cells in the retina called the retinal pigment epithelium (RPE) in tissue developed from birdshot patient stem cells.

“Subtle changes to RPE can be seen in some patients during the early stages of birdshot. This is not an obvious feature of the condition but current examination methods are limited, identifying only severe dysfunction,” says Dr Gonzalez Cordero.

“We do know that RPE can modulate the choroid and that RPE cells show HLA-A29 gene activity. Almost everyone with birdshot has a particular variation of this gene. Post-mortem tissue from birdshot patients is both scarce and unsuitable for detailed analysis. However we can develop mature RPE in the lab from stem cells derived from blood of living patients. This will allow us to explore the role of RPE in detail as well as providing a much-needed test bed for future treatments that can also be used by other researchers in the field.”

Iron overload is treatable

Dr Graham Wallace at the University of Birmingham will lead the second study. Here the focus is on genetic control of iron levels in birdshot.

“Iron is essential in the retina for photoreceptor cell function and is generally controlled by iron-regulating proteins. However free iron is highly toxic for photoreceptors, leading to an increase in oxidative stress. Iron is also involved in inflammation as it is essential for the proliferation of immune cells,” says Dr Wallace.

“Given a recent association between HLA-A29 and HFE H63D – a gene implicated in patients with iron overload – we think this could be an important route to explore with regard to birdshot. Iron overload is treatable and so may give us other options.”

Dr Dolores Conroy is Fight for Sight’s Director of Research. She says: “Understanding the root causes of birdshot is ultimately what will lead us to targeted, effective treatments. The Sight Loss and Vision Priority Setting Partnership tells us that this is what’s important to patients and so we are delighted to partner with Birdshot Uveitis Society to see the priorities addressed.”

Annie Folkard, a founder of the Birdshot Uveitis Society, said: “We are excited to support this innovative research. Studies likes these give our members great hope that in the future, improvements will be made to the current toxic treatments. Maybe even a cure will be found.”

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