To prove the theory that toxic RNA is involved in myotonic muscular dystrophy, a research team led by Dr. Mani Mahadevan, a University of Virginia pathologist, duplicated the disease in mice. "We showed in our mouse model that when you make this poisonous RNA the mice get various aspects of myotonic dystrophy," Mahadevan said. "Then, when you take away the toxic RNA, the mice get back to normal."

Mahadevan and colleagues created a new type of mouse model with many extra copies of the CTG repeats, each attached to DNA for a protein that glows green under a microscope. They also integrated an "on switch" for MMD in the mice, activated by giving them doxycycline, an antibiotic, in their drinking water.

When mice began to produce many copies of RNA with CTG repeats, they developed the hallmarks of type 1 MMD within a few weeks, including an inability to relax muscles and heart rhythm abnormalities. When doxycycline was stopped, mice stopped producing toxic RNA and returned to normal, except in cases when the heart was severely damaged.

So far, however, Mahadevan and other scientists can not explain exactly what happens inside the cell to cause someone to get myotonic dystrophy. "The prevailing theory is that the RNA remains in the nucleus, rather than moving out of it, and proteins get stuck to the RNA and aren't able to do their job," Mahadevan said.

This toxic RNA in not found in every cell of the body, Mahadevan said. Rather, it is produced in higher levels in muscle cells, in the heart and brain, in the lining of the intestines and in the lens and muscles of the eyes.

MEDICA.de; Source: University of Virginia