Many of us take for granted our ability to control our bodies and muscles. We type on keyboards and stretch at our desks without much thought. However, such everyday actions can be challenging for children with early onset genetic dystonia — the most common form is called DYT1 — who begin to experience involuntary twisting movements, usually in a foot, leg, or arm, around age 10. Within two to three years, the muscle contractions can affect all of their body parts.
A team of scientists at The Children’s Hospital of Philadelphia are comparing two molecular therapy techniques — RNA interference (RNAi) and antisense oligonucleotides (ASOs) — to help answer critical questions in the field of DYT1 research. Could the symptoms of this disabling neurological disorder that affects about one in 30,000 Americans be reversible? And what are the biological bases of DYT1’s characteristic motor dysfunction?
“In contrast to many other brain diseases that affect motor function, there is no known loss of brain cells in DYT1,” said Pedro Gonzalez-Alegre, MD, PhD, principal investigator of the research project that recently received funding for three years from the U.S. Department of Defense (DOD). “The brain cells just are not working properly, so there is a lot of potential for this to be reversible.”
Scientists know that the mutated gene TOR1A causes DYT1. The TOR1A gene provides instructions for making a protein called torsinA. When TOR1A is mutated, it produces an altered torsinA protein that may disrupt chemical signaling between nerve cells that control movement. In previous research, Dr. Gonzalez-Alegre achieved successful gene silencing in cultured cells using RNAi and ASOs to prevent neurons from making the mutated or “toxic” protein.
“If we can eliminate the expression or down-regulate the expression of this gene, could that restore normal brain function?” Dr. Gonzalez-Alegre asks in the current research project.
The study team will test their theory in rats bred to express the human DYT1 mutant gene. They will pursue the two complementary gene silencing approaches in parallel, measure if they are able to reverse or improve DYT1-linked motor dysfunction, and observe if any side effects occur.
First, the scientists have designed ASOs that they will deliver directly into the rats’ central nervous system in order to broadly suppress TOR1A’s toxic activity. ASOs block disease processes by altering the synthesis of a particular protein.
Next, the study team will rely on the expertise of co-investigator Beverly L. Davidson, PhD, director of CHOP’s Center for Cellular and Molecular Therapeutics, who has pioneered methods that allow scientists to infuse RNAi into cells via viral vectors to individually turn off genes associated with brain disease. They will introduce RNAi into parts of the rats’ brains called the striatum and cerebellum. Pinpointing these brain regions as the primary sites responsible for DYT1 dysfunction could help to establish anatomical targets for future therapeutics.
Only about 30 percent of people who carry the DYT1 mutation go on to develop symptoms, Dr. Gonzalez-Alegre pointed out, so he is encouraged that these investigations will show evidence that the inherited disease is potentially reversible. If they can demonstrate that DYT1 is an ideal candidate for gene silencing, the study team will be on track to develop novel treatments to improve the quality of life of patients.
Dr. Gonzalez-Alegre cares for DYT1 patients as a movement disorder neurologist and works closely with The Dystonia Medical Research Foundation, which has successfully lobbied the DOD to include dystonia in its list of medical conditions eligible for funding under the Congressionally Directed Medical Research Program. In addition to inherited dystonia, many other types of dystonia can occur, such as in veterans who experience a traumatic brain injury.
“By studying the genetic form of dystonia, we hopefully will learn new things that can expand our understanding of multiple forms of the disease,” said Dr. Gonzalez-Alegre, who is also an associate professor of neurology in the Department of Neurology at Penn Medicine.