Stem cell therapy could soon be used to treat what is, at present, incurable blindness caused by retinitis pigmentosa (RP), an inherited degenerative disease affecting the retina of the eye, associated with a gradual loss of vision. The retina is composed of a layer of cells responsible for sensing light in the human eye. Retinitis pigmentosa is a disorder in which the retina’s ability to respond to light is impaired due to a genetic mutation which prevents the necessary proteins from being formed. Those afflicted with this condition suffer a slow loss of vision starting with poor night vision and a loss of peripheral (side) vision and eventually leading to total blindness. There is, unfortunately, no cure for the disease.
Until now, that is. Scientists at Columbia University and the University of Iowa have been working in collaboration to use a gene-editing technique called CRISPR/Cas9 to repair the damaged gene that results in RP. The process involves obtaining skin cells from patients with retinitis pigmentosa and converting them into pluripotent stem cells that have the ability to transform into other cell types. Patients with RP have a mutation in the RPGR gene, and the researchers have utilized the CRISPR gene editing technique to correct this mutation and render the cells healthy again, according to the study published in Scientific Reports.
The editing technique needs to be extremely precise to correct the mutation in the RPGR gene without damaging any other areas of the genome. Study leader Dr. Vinit Mahajan hopes to initiate human trials in which stem cells with a corrected version of the RPGR gene will be transplanted into the eyes of patients with retinitis pigmentosa to cure their blindness. He is excited by the possibilities offered by the CRISPR technique as a means of transplanting healthy cells to fix genetic mutations, offering real hope for patients with previously incurable diseases.
The research is not yet complete, and the technique must be refined and tested further to ensure that it is safe for humans. Dr. Stephen Tsang, co-contributor on the study, indicates that the scientists are now working on ensuring that they are able to precisely change the single mutation in the RPGR gene without making other harmful alterations in any other genes.
Although RP is classified as a rare disorder, affecting 1 in 4,000 people, there are currently approximately 100,000 people living with blindness due to RP in the United States alone. The disease manifests in childhood with difficulty getting around in the dark and tripping over things. People with RP often experience photophobia or discomfort with bright lights. There are many gene mutations that can result in RP, and the disease spectrum can vary from people retaining central vision well into their 50s to severe forms of the disease where the person becomes legally blind by early adulthood. Eventually, most people with RP lose their sight.
Gene therapy utilizing stem cells is aimed at preventing vision loss and restoring sight in people with retinitis pigmentosa. People like Elizabeth Troutman, who lost sight at age 25 due to RP. Success in these gene-editing techniques will mean Elizabeth will one day be able to see the sun rise and know what the smiles and frowns of her children look like.