May 1, 1998 CHAPEL HILL - A possible new form of gene therapy designed to mask genetic mutations - instead of cutting away and replacing them -- has been developed by scientists at the University of North Carolina at Chapel Hill School of Medicine and Bern University in Switzerland.
The technique, so far limited to laboratory cell cultures, involves using small RNA molecules to block defective processing, or splicing, inside cell nuclei of a messenger RNA that codes for a blood protein known as beta-globin.
Since the short RNA fragments block the faulty processing sites, cells' splicing machinery can only use functional, non-mutated locations, researchers say. What results is steady production of healthy "messengers," which then relay accurate genetic instructions into cell cytoplasm where normal proteins assemble.
A report on the research appears in the April 28 issue of the Proceedings of the National Academy of Sciences. Authors include pharmacology doctoral student Linda Gorman and Dr. Ryszard Kole, professor of pharmacology at UNC-CH.
"This work offers real hope that one day we will be able to cure - not just treat -- beta thalassemia, an inherited deficiency of hemoglobin, the essential protein that carries oxygen and gives blood its red color," said Kole, a member of the UNC Lineberger Comprehensive Cancer Center. "We are still a few steps away from trying this in patients, but it is quite promising."
Like sending imperfect plans to a factory, errors in messenger RNA production result in defective or inadequate protein production, he said. In severe cases of untreated beta thalassemia, those errors lead to acute anemia and death at a young age.
"The advantage of our novel way to block the incorrect splice sites is that the chances of doing something inappropriate to genes are minimal," Kole said. "A limitation would be that you can't just cut out the whole gene and put in the correct one. You have to know exactly what the specific mutation is and target it."
In their work, Gorman, Kole and collaborators introduced modified RNA molecules into cells containing mutated genes that cause beta thalassemia, which is common in Cyprus, the Middle East and Southeast Asia. They modified the molecules by incorporating into them sections of RNA complementary - something like a mirror image - to the defective sites.
"Adding these modified molecules led to increased levels, about 65 percent, of correctly spliced messenger RNA that carried the code for globin, a sub-unit of hemoglobin," Kole said. "While this research demonstrates that such molecules can be permanently established in cultured cells, the ultimate aim is to incorporate such particles into patients' bone marrow where red blood cells, which carry hemoglobin throughout the body, are produced."
The new gene therapy technique might work with many other genetic illnesses as well, he said.
Co-authors of the report are Drs. Victoria Emerick of SmithKline Beecham in Collegetown, Pa., and Drs. Daniel Suter and Daniel Schumperli of Bern University's Zoological Institute.
The National Institutes of Health, the Roche Research Foundation and the Swiss National Science Foundation supported the research.
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