MARKER OF DEGENERATION: Scientists revealed that changes in the blood begin to take place more than 15 years before neurological symptoms of Huntington's disease turn up. Image: © ISTOCKPHOTO/BOGDAN POP
Researchers have discovered early blood markers in people genetically predisposed to develop Huntington's disease, a mysterious neurodegenerative disorder. These signs may provide future targets for staving off or even preventing symptoms from developing.
Huntington's disease, which affects an estimated 30,000 Americans, kills neurons (nerve cells), which leads to cognitive difficulties, a loss of movement control and emotional distress. A carrier typically does not experience symptoms until he or she is in her 30s or 40s, and lives an average of 15 to 20 years once they show up. Patients ultimately die of heart failure, pneumonia or choking triggered by the disorder. Children with a parent who has the disease have a 50 percent chance of inheriting the mutated huntingtin gene that causes it.
In other neurodegenerative diseases, such as Parkinson's—which primarily affects a person's motor abilities—scientists know that nerve cells begin to die long before symptoms appear. Researchers wondered if the same was true in Huntington's. Previous research indicated this was the case in mice, but this is the first study to document presymptomatic dysfunction in humans.
"In gene carriers, before they show signs of the disease, the neurodegeneration process has already started," says Sarah Tabrizi, a neurologist at University College London and coauthor of the study, which appears in The Journal of Experimental Medicine. "This indicates that the process of neuronal dysfunction which goes on to neuronal degeneration is theoretically rescuable."
Tabrizi and her team collected blood samples from 194 people with the gene to determine whether there were early markers that could be targeted to delay the disease's onset. They found that they all produced an excess of cytokines (immune system scouts that signal other disease-fighting cells to combat invading germs or to fix damaged tissue)—some as early as 16 years before researchers would have expected symptoms to appear.
Study co-author Thomas Moeller, a neurologist at the University of Washington in Seattle, speculates that the cytokines—which are also produced in excess by immune cells in the brain called microglia--may be killing or contributing to the death of healthy neurons, leading to symptoms down the road. He says that if researchers can design a drug that keeps these cells at bay, they may be able to slow the progression of the disease.
Paul Patterson, a biologist at the California Institute of Technology, says this is the first evidence in humans that aggressive immune cells may play a role, which his team previously discovered was the case in mice. He says the finding is key, because it could pave the way to use cytokine levels to gauge the effectiveness of new therapies developed to fight Huntington's. If they go down, it will indicate a drug is working.