People with Huntington disease carry the genetic mutation from birth, but why do some people develop symptoms much earlier than others?That is the question scientists from UBC’s Centre for Molecular Medicine and Therapeutics and BC Children’s Hospital Research Institute were looking to answer in a study into why some patients experience disease onset 10 to 12 years earlier than others.Researchers say they have found an important clue that can explain the difference.According to a study published Monday in the scientific journal Neuron, a particular genetic variant appears to accelerate the disease by “driving runaway DNA changes” in the brain’s most vulnerable neurons.“People with this genetic variant have dramatically hastened onset of disease, but we didn’t know why,” said senior study author Dr. Michael Hayden, professor at the Centre for Molecular Medicine and Therapeutics at UBC and investigator at BC Children’s Hospital Research Institute.“This work answers that question and provides dramatic evidence that repeated expansion of the mutation is an important driver of Huntington disease and a potential treatment target.”Huntington’s is an inherited, progressive disorder that causes involuntary movements and psychiatric problems, UBC says. The mutation is present in every cell of the body, the university says, but damage is primarily centred in nerve cells in the brain.People with the genetic variant had much larger expansions of the Huntington mutation in their neurons, with the expansion happening about five times more frequently than in patients without the variant, UBC says.UBC says the study results might help explain why Huntington’s is primarily a brain disease, even though the mutation is present in every cell in a patient’s body.Could this increased understanding improve treatment? The study authors say the findings give scientists some of the strongest evidence to date that expansion of the mutation is a key factor in the progression of the disease.“It validates repeat expansion of the DNA as an important therapeutic target in Huntington disease,” Hayden said.“If we can suppress that expansion, it may be possible to delay progression or delay the onset of disease.”