Gene therapy for retinitis pigmentosa

An international team of scientists and clinicians from the United States and Saudi Arabia are working to develop gene therapy for treating a rare, hereditary retinal disease.

The therapy has been shown to restore lost vision in animal models of retinitis pigmentosa (RP). Their work is being funded in part by a $1.5 million grant from the Prince Salman Center for Disability Research in Saudi Arabia, where the recessive gene mutation that leads to the eye disease RP has been found in children from several families.

The study is being led by Kang Zhang, MD, PhD, professor of ophthalmology at the University of California, San Diego School's Shiley Eye Center and director of the UCSD Institute for Genomic Medicine, and Fowzan Alkuraya, MD, senior clinical scientist and head of developmental genetics unit at King Faisal Specialist Hospital and Research Center, Saudi Arabia.

RP is a type of hereditary retinal dystrophy, a group of inherited disorders in which abnormalities of the photoreceptor rods and cones lead to progressive visual loss. Rods and cones are specialized light-sensitive nerve cells that line the retina. They collect light and then send nerve signals that the brain interprets as vision. Rods facilitate black and white vision and are used mainly at night. During the day, humans depend on cones for color vision.

In people with the genetic mutations that cause RP, rods and cone cells die. Affected individuals first experience defective dark adaptation or "night blindness," followed by reduction of the peripheral visual field known as tunnel vision, sometimes followed by loss of central vision late in the course of the disease. RP affects one in 3,000 to 4,000 people in the United States.

The planned clinical approach of this research trial involves a receptor protein called MERTK that is expressed in the retinal pigment epithelium, the pigmented cell layer just outside the retina that closely interacts with photoreceptors in the maintenance of visual function. Patients with loss of MERTK function have a defect in phagocytosis - a mechanism used to remove pathogens and cell debris. As a result of this defect, debris accumulates between the photoreceptors and retinal pigment epithelium, resulting in death of photoreceptors and loss of vision.

The researchers plan to deliver the MERTK gene in a viral vector - a carrier commonly used to deliver genetic material to treat these cells in order to restore function of photoreceptors. Using a rodent model of RP with a similar MERTK mutation, the researchers have demonstrated in proof-of-concept studies that viral vector delivery of MERTK corrects the mutant gene and restores vision.

The eye is an ideal place for gene therapy because it's an "immune-privileged site," meaning that the eye is able to tolerate the introduction of foreign cells with a minimal, if any, inflammatory immune response, according to Zhang.

The research team's next step is to show that such gene therapy is safe in further animal studies, to be conducted in China, along with additional rat studies that will be conducted at UC San Diego and at the University of Florida.

Once safety for the procedure has been shown, the team hopes to proceed to a human clinical trial in seven patients identified in Saudi Arabia, perhaps as early as spring of 2010.

The same type of vector has been successfully tested in both animals and humans for a similar type of early-onset retinal degeneration called Leber's congenital amaurosis.

Additional investigators include William Hauswirth, PhD, at the University of Florida, Gainesville; SriniVas Sadda, MD, at Doheny Eye Institute, University of Southern California; Emad Abboud, MD, and Hisham Alkuraya, MD, at King Khaled Eye Specialist Hospital, Saudi Arabia; and Peiquan Chao, MD, PhD, Department of Ophthalmology, Shanghai Jiaotong University.


  1. cory martin cory martin United States says:

    I am very excited about this study. I have a 10 year old boy with x linked RP. He is currently involved in a 4 year reaserch study with omega 3 capsules

    • Terri Terri United States says:

      Hi.  I just read your comment that your son is involved w/ a study involving Omega 3 for RP.  I am wondering how it is going and if he is finding any benefits?  I've been diagnosed w/ RP for 21 years (since age 21.)  Thanks and best wishes...  Terri   E-mail:  [email protected]  

    • catherine morales gabriel catherine morales gabriel Philippines says:

      I have been diagnosed with retinitis pigmentosa for 5 years, now I am losing my sight, I need help please. I have 3 kids and I am 31 years old. Don't want to go blind this young and my kids need me, please tell me what medicines could help me delay my blindness, Thank you so much.

  2. Terri Terri United States says:

    This is exciting news.  I was diagnosed w/ RP 21 years ago.  I also was diagnosed with MS 16 years ago.  I'm looking forward to the upcoming testing of stem cells and gene therapy so hopefully it can help me with both diseases!

  3. Jasmin Jasmin Saudi Arabia says:

    Hello, we are interested in the gene therapy and we would like to have more information about it.

    We were wondering if we could contact anyone who could help us/ give us more information about it.

    We are waiting for your answers Thank You

  4. Heidi Heidi United States says:

    I was diagnosed with RP, Usher II when I was 32 (8 yrs ago) and was told to take vitamin A palmitate, which I didn't because I wanted to have babies and I did have my babies first.  Now, I was tested and have lost so much vision.  I'm taking it more seriously now and take vitamin A(15,000 IU) and DHA 200 mg. to help slow down the disease so I don't lose more than I have to.  If I had taken these when I was younger (in between babies) I probably would of slowed down the disease more and have had more vision still.  I wouldn't trade my babies for any amount of vision, but I am very faithful at taking my vitamins now.  I don't want to lose my vision either.  I have 7 kids of my own and 2 stepchildren.  I want to see my grandbabies' faces and all those things you take for granted when you have vision.  I am hoping for a cure or treatment and would be so happy if they could figure out how to stop any more loss and I could keep what vision I have left.  Enjoy every day and every sight while you have it!  They are blessings that some don't realize how precious they are.

    • zarina zarina Malaysia says:

      Hi Heidi,

      My son has been diagnosed with RP , he is 8 but I can clearly see the symptoms , he has fallen many times and received stitches , we the parents, did not suspect that it was his vision. We feel very bad . How much vitamin A can i give him per day ? woudl you know ?

      zarina from malaysia

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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