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Understanding female IRD carriers

Research into X-linked inherited retinal diseases often focuses on males, but a study at CERA is aiming to make sure everyone benefits from newly developed treatments.

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Inherited retinal diseases (IRD), a broad group of genetic eye conditions caused by changes in a person’s genetic code, do not always affect men and women in the same way.

“A majority of female carriers of X-linked IRDs have a near-normal retina, while at the other end of the spectrum is quite severe disease, similar to what males with these conditions experience,” says Sena Gocuk, optometrist, CERA researcher and PhD candidate at the University of Melbourne.

The condition of many female carriers can often be so mild that it is only identified after a male relative is diagnosed with an inherited disorder.

This lesser severity has led past research to focus only on males with these diseases, but a new study at CERA is seeking help change that.

Operating instructions

Chromosomes, the thread-like structures located inside the nucleus of living cells, contain the instructions for how those cells should operate.

They also determine a person’s biological sex; females have two X-chromosomes and males have one X-chromosome and one Y-chromosome.

For IRDs caused by changes in the DNA code of eye genes found on the X-chromosome, the sexes can be affected in very different ways.

“Conditions like choroideremia, and some forms of retinitis pigmentosa, are X-linked conditions, meaning they are caused by faults in the X-chromosome,” says Gocuk.

“For males, who only have one X-chromosome, a single copy of the mutated gene means that they will develop the retinal condition.”

For females, who have two X-chromosomes, an X-linked retinal condition may present quite differently – with some women having no symptoms, and others noting changes in their vision.

“If a female has one mutated and one normal gene, individual cells decide which of the two X-chromosomes are expressed,” says Gocuk.

“Because of that, you get a wide spectrum of disease severities.”

Participants will receive genetic testing and a comprehensive eye examination.
Survey and study

The study involves clinical visits, where Gocuk will learn more about the eye health of female carriers of these X-linked retinal diseases.

Participants will receive genetic testing and counselling, undergo a comprehensive eye examination to assess their retinae, and also have the opportunity to continue in the study to monitor how their vision changes over time.

In another part of her study, Gocuk is asking mothers, sisters and daughters of males with X-linked IRDs to complete an online survey, in order to develop a better understanding of how the condition affects women, and also their opinion of whether future gene therapies might potentially benefit them.

“Questionnaires that have looked at female carriers of other genetic conditions have found a lot of women experience shock, guilt and anxiety when their male relatives are diagnosed,” says Gocuk.

“One of my participants became quite teary when speaking with me about her experiences, because she has a number of male relatives with retinitis.

“She knows that this research might not benefit her or her children, but she wants to contribute.

“It’s been quite rewarding to hear these stories.”

Gocuk is a recipient of the University of Melbourne’s Harold Mitchell Postgraduate Travelling Fellowship, and will use the funds to travel to the University of Oxford to examine 10-year data from a UK longitudinal study as part of the project.

Her work is also running alongside another ongoing study at CERA, surveying people who are living with an IRD.

Gocuk says she hopes her research might help lay the groundwork to see whether more people can benefit from emerging genetic treatments.

“I would be pleased if we were able to determine if some of these women would be eligible for emerging treatments, like gene therapy.

“It would be quite rewarding, and potentially life changing for this group of people.”

If you think you’re a female carrier of an X-linked inherited retinal disease or would like further information, please email Sena Gocuk: sena.gocuk@unimelb.edu.au.

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