Why Does a Particular Genetic Variant Lead to Accelerated Huntington Disease Development?

Scientists at the University of British Columbia have discovered why some individuals with Huntington disease (HD) experience an earlier onset and more severe symptoms. The research, led by Michael Hayden, explains how a specific genetic variant can significantly accelerate the progression of the disease. This variant causes a rapid expansion of the mutation within vulnerable neurons, leading to earlier and more severe symptoms of HD.

The study, published in Neuron, reveals that individuals with this genetic variant have a much faster onset of HD motor symptoms, up to 12.5 years earlier, and a more rapid clinical progression. The researchers analyzed blood samples and post-mortem brain tissue from HD patients with and without the genetic variant. They found that the variant leads to a much larger expansion of the Huntington mutation in the brain's medium spiny neurons, which are particularly susceptible to damage in HD.

This selective expansion is highly concentrated in certain brain cells, explaining why the mutation primarily affects the brain despite being present in every cell. The findings suggest that blood tests may not accurately reflect the progression of HD in the brain, as the mutation's expansion is more pronounced in the neurons. The study provides strong evidence that repeat expansion of the Huntington mutation is a key driver of disease progression in HD and a potential target for future treatments.

Suppressing this expansion could potentially delay the onset or progression of the disease. The researchers emphasize the need for cell-type-specific studies in other repeat expansion disorders to better understand their impact on specific neuron populations.