“Huntington’s is a ticking time bomb. If one of your parents had it, you have a 50 per cent chance of inheriting the mutated gene for it. And if you have the mutated gene, then you will develop the disease,” emphasizes Dr. Massimo Pandolfo, a neurologist and co-director of The Neuro’s Clinical Research Unit, speaking about Huntington’s Disease (HD), a progressive severe, disabling neurological disorder brought on by a gene mutation. It strikes in the prime of life with a crushing decline that leads to physical, psychological, and cognitive losses.
Damaged gene
The disease is due to a genetic mutation in the HTT gene that makes a protein called huntingtin. We all have so-called CAG repeats (Cytosine, Adenine, Guanine) in this gene, but people with the disease have a greater number of CAG repeats than usual. These drive cells to manufacture a mutant form of huntingtin, which eventually causes nerve cells (neurons) to gradually break down and die in an area of the brain responsible for control of movement, cognition and emotion.
Huntington’s Disease is very difficult for affected individuals and their family. “Often, the first changes are psychiatric. Individuals behave uncharacteristically – make bad choices, change personality. Next, they develop difficulties with planning and complex tasks, progressively leading to dementia and they also develop a movement disorder with uncontrolled twists and twitches,” explains Dr. Pandolfo.
The disease may appear at different ages because of the unstable nature of the mutation. The number of CAG repeats in the HTT gene is a major factor determining when symptoms appear; the longer the repeat, the earlier the onset. As the repeat may change in size when transmitted form the affected parent, a child may develop the disease at a younger age than their parent, a phenomenon called anticipation. When starting very early, Huntington disease may result in generalized rigidity and slowness instead of the typical twists and twitches.
A common rare disease
According to the Huntington’s Society of Canada, 1 in 7,000 people in Canada are affected. Symptoms usually begin in the prime of life between 35 and 55, and life expectancy is 10 to 25 years after the start of symptoms. There are currently no drugs to slow or stop its progression.
For the first time, the Clinical Research Unit at The Neuro will conduct several clinical trials into Huntington’s Disease, continuing to expand the list of conditions covered in its clinical trials. In the past year alone, the CRU added trials for rare diseases like MOGAD and Facioscapulohumeral muscular dystrophy (FSHD) as well as a rapidly progressing prion disease known as Creutzfeldt-Jakob.
Decreasing the gene expression
“Currently, healthcare teams use medication to treat the depression, the psychiatric issues, and decrease the involuntary movements,” says Dr. Pandolfo. “But ideally we would correct the genetic defect that causes this debilitating disease.”
Some of the new approaches being investigated try to decrease the expression of the mutated gene so that it makes less of the toxic Huntingtin protein in the hopes that this will slow the progression of the disease.
“A number of studies have identified symptoms that precede obvious clinical onset of Huntington’s, that is to say the moment when individuals begin to have very subtle changes in mood and movement. Developing an effective therapy would allow us to eventually intervene at this pre-symptomatic stage and delay the onset of disease as long as possible,” says Dr. Pandolfo.
For more about studies on Huntington’s Disease at The Neuro’s Clinical Research Unit, visit cru.mcgill.ca/mvtdisorders, contact neurocog-cru.neuro@mcgill.ca or 514-398-5500 for more information.