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Scientists Fix Retinitis Pigmentosa in Patient-Derived Stem Cells With CRISPR/Cas9

NEW YORK (GenomeWeb) – Scientists from Columbia University and the University of Iowa have fixed a genetic defect causing the eye disease retinitis pigmentosa (RP) using CRISPR/Cas9 gene editing in induced pluripotent stem cells derived from a patient with the disease.

The scientists, led by first author Alexander Bassuk and co-senior author Vinit Mahajan of the University of Iowa and co-senior author Stephen Tsang of Columbia University, corrected a point mutation in the RPGR gene using the homology directed repair pathway to incorporate the wild-type allele. They published their results today in Scientific Reports.

The results suggest ex vivo therapies that reintroduce autologous, edited iPSCs to a patient's eye could work.

"We still have some way to go, but we believe that the first therapeutic use of CRISPR will be to treat an eye disease," Tsang said in a statement. "Here we have demonstrated that the initial steps are feasible."

RP is a congenital disease characterized by retinal dystrophy that causes blindness in approximately one in 4,000 people. Tsang has worked extensively on stem cell-based therapies for retinitis pigmentosa over the last several years. In 2012, he led a group of scientists that showed human iPSCs from a healthy donor could be safely and efficaciously transplanted into a mouse model of the disease.

In the experiment published in Scientific Reports, the researchers first created iPSCs from skin fibroblasts of a patient with RP. They then transduced guide RNAs, the Cas9 enzyme, and a donor homology template to edit the target site.

They reported that 13 percent of RPGR copies showed the correction to the wild-type allele.

"The X-linked form of retinitis pigmentosa is an ideal candidate for a precision medicine approach because a common mutation accounts for 90 percent of cases," Tsang said.

Currently, the only treatment for RP is high doses of Vitamin A, which slows vision loss. Non-CRISPR gene therapies are in development but do not permanently correct the defective gene.

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