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The Genetics Behind Retinal Dystrophies

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I spend my days considering patients with inherited retinal diseases (IRDs). These are conditions where there’s dysfunction in the cells of the retina, a layer of tissue in the back of your eye that sends light signals to your brain. These are caused by gene mutations, which means there’s at least one gene that isn’t operational as it should. But while IRDs can affect people of any age, gender, or race, they have one shocking thing in common: They can lead to severe vision loss, and perhaps even blindness. Here’s what’s important to know about these diseases.Genes are small sections of DNA — your body’s hereditary material — that contain instructions for specific proteins your body needs. Some help build bone, some determine eye colors, others allow your strength to move or your heart to beat. Sometimes, there’s a change in a gene’s DNA sequence, which is known as a variant. This can cause one of these proteins to not work correctly.
There are more than 300 genes now known to play a role in an IRD. They have a wide range. Some are genes that are specific to the retina itself, while others play a role in other parts of the body. It’s not always clear why some people with these gene mutations experience problems just with their retina and not in organs, like their lungs or liver. Unfortunately, you just need one gene variant, or mutation, to cause your retina to not work properly.The most common IRD is retinitis pigmentosa, a disease where the light-sensing cells of the retina gradually die off. It can appear either during childhood or later, during adulthood. While it initially starts as loss of night vision, it progresses to loss of peripheral (side) vision and may eventually affect your central vision, as well.

Other IRDs include Stargardt disease, which causes injure to the macula, a small area in the center of your retina; cone-rod dystrophy (CRD), which damages the light-sensitive cells in the retina; and Leber Congenital Amaurosis, which is similar to retinitis pigmentosa but often more harsh.
IRDs Are Passed downward to You From Your Parents
Many of my patients are surprised to hear this, especially if up until now there’s been little to no family history of the disease. But we get two copies of each gene, one from your mother and one from your father. There are fundamentally three basic legacy patterns:

Autosomal dominant. This is when you accept one copy of a variant leading gene from one parent, and one unchanged gene from the other parent. Since the alternative dominant gene causes the disease, if you get it, you’ll develop the disease itself. If a person themselves has the disease, their chances of passing it to their child is 50%.Autosomal recessive. This is when you receive two recessive variant genes from each parent. This can often be silently passed down through generations, since parents are just carriers. They have one normal gene, and one variant copy. If both parents are carriers, there’s a 25% chance that each child they have will inherit both genes and develop the IRD. Even if they don’t, there’s a 50% chance that they will still be a carrier.X-Linked disorders. Some genetic variants are located on the X chromosome and can cause X-linked disorders. These are much more ordinary in males than females. Why? Females have two X chromosomes, so they can carry one diseased gene and one healthy one. But since males have only one X chromosome, they’re more probable to be genetically susceptible. A good example of this is X-linked retinal pigmentosa. While women can still get it, they’re much less likely to be harshly precious.
Genetic Testing Is Important
If we think you have an IRD, we will do a slew of clinical testing. This includes:

Electroretinogram (ERG). An ERG sends a flash of light to your retina and has electrodes to measure its response. People with IRDs tend to have decreased electrical activity, due to poor function of retinal cells like photoreceptors, which send light signals to your brain.
Visual field testing. Your doctor will have you watch a dot of light move around a half-circle directly in front of you and have you push a button whenever you see a light. This will help them determine the extent and location of your vision loss.
Genetic testing. This is the most important part, as it tells you the exact type of IRD you have. Your doctor will take a blood or saliva sample and send it off to a lab for testing. This can help them identify potential treatment options, including clinical trials you may be a candidate for. It will also let you know whether other family members may be at risk, and, in some cases, identify whether you’re at risk for other health problems.
Gene Therapy Is the Wave of the Future
Gene therapy — a type of treatment where a new gene is delivered to targeted cells in the body — looks especially promising for IRDs. Unlike other parts of the body, the eye is small, easy to access for treatment, and less likely to attack a foreign substance when it’s injected into it.

It’s good to be aware of all the different clinical trials out there. One way to do that is to participate in patient data registries such as My Retina Tracker (fightingblindness.org/my-retinatracker-registry). It’s free and is a way to learn about new clinical research. More importantly, it gives people hope. Even if there’s only one approved gene therapy out there, there are so many trials compared with a decade ago. While these new targeted treatments may not be ready for prime time just yet, there’s plenty in the pipeline to help you stay optimistic.
It can be devastating to be diagnosed with an inherited retinal dystrophy (IRD). These rare, inherited eye diseases cause progressive vision loss, and sometimes even blindness. Here at the Cleveland Clinic, we’ve seen more patients than ever before with IRDs. Our numbers have risen from 327 patients in 2015, to almost 800 in 2019. The reason? We’ve become much better at both diagnosis and treatment.Over the last 2 decades, we’ve learned that there are around 300 genes associated with IRDs. Thanks to advances in genetic testing technology, we’re able to diagnose the gene mutations in over 70% of all cases.

That’s great news, because once we know what genetic mutation is driving your disease, we can often refer you to an appropriate clinical trial that may help improve or maintain your vision. Even if we can’t now, thanks to gene therapy, there’s a very real chance that in the next decade or two, there may be a revolutionary new treatment to save your sight.Here’s why we’re so excited about gene therapy, what’s available now, and how to go about finding a clinical trial near you.
Why Gene Therapy for IRDs Is So Promising
In gene therapy, an abnormal gene is replaced with a normal one. While there are many ways to do it, the most common way is to use a vector — a virus without the disease-causing parts — to deliver a healthy gene into the cells. This is done through surgery to the eye by a physician. The hope is that the cells with the new, functional copy of a gene will now work properly.

As it turns out, the eye itself is really an ideal applicant for gene therapy. There are a couple of reasons for this. One is that the retina itself is relatively easy to reach compared to other parts of your body, like your heart, or lungs. The second is that the eye is “immune privileged.” This means its resistant response isn’t as active as in other parts of the body. That’s important, since when a virus vector with a normal gene is injected into the eye, you don’t want the eye’s immune answer to go into overdrive.

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