A Brain-Destroying Prion Disease Is Becoming More Common, Study Finds

A Brain-Destroying Prion Disease Is Becoming More Common, Study Finds
An image of a human brain tissue specimen under a microscope. It displays the telltale spongy holes caused by Creutzfeldt-Jakob disease. (Image: Sherif Zaki, Wun-Ju Shieh/CDC)

New research from Japan suggests that a rare brain-destroying disease caused by rogue prion proteins may be becoming more common — likely due to an ageing population.

The study, published last month in the journal Scientific Reports, looked at data collected by the Japanese government from 2005 to 2014 on residents over the age of 50 who were diagnosed with Creutzfeldt–Jakob disease (CJD). During those years, the study found, the average incidence rate of CJD rose by 6.4 per cent annually. This rise was most pronounced among people over the age of 70, but the pattern held even when the researchers accounted for age.

“Our study revealed an increase in the absolute number of deaths, mortality rates, and incidence rates associated with CJD — even after age-adjustment — in Japan between 2005 and 2014,” they wrote.

Prion diseases like CJD are caused by the misfolded form of naturally existing and thought to be harmless prion proteins in the brain. These wayward proteins have the uncanny ability to convert other normal prions to fold like them, which triggers a very slow-moving cascade of destruction that spreads throughout the brain and leaves behind characteristic spongy microscopic holes, which can be seen in the victim’s brain after death. Symptoms like dementia and loss of muscle control may not appear for years to decades, depending on the prion disease, but once they do, death quickly follows. To date, there are no available treatments for prion diseases, and their fatality rate is 100% upon the onset of symptoms.

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Some prion diseases are transmissible between people or from animals to people. A person becomes infected after being exposed to brain or organ tissue contaminated with prions (including via cannibalism). Others are inherited, caused by genetic mutations that make the bad prions more likely to appear at some undetermined point in your life. Most of the time, though, the prions seem to show up for no clear reason, called sporadic prion disease. CJD comes in all three forms, though sporadic CJD is the most common version, accounting for 85% of cases. Whatever the form, CJD is the most prevalent prion disease in people.

Though there’s no single cause for most cases of CJD, age is thought to be an important risk factor. And this current study isn’t the first to highlight an apparent rise in CJD over time that’s linked to age. Other research has found similar trends in many countries, including the U.S. But Japan is known for having the largest elderly population in the world, with more than 20 per cent over 65. So it’s likely that any age-related link to CJD will be more pronounced there — a fate that the researchers are understandably concerned about.

That said, CJD and all prion diseases remain rare. In 2017, for instance, only 511 Americans were diagnosed with CJD, according to the Centres for Disease Control and Prevention. But these mysterious diseases may be the most brutal reminder of the stresses that will come with an ageing population, both in Japan and elsewhere. Other causes of dementia, such as Alzheimer’s, are expected to rise in incidence in the years to come as well, and may especially impact places like the U.S., where the rate of other chronic conditions for older Americans has also increased over time.

CJD and other forms of dementia won’t just affect the people who develop them, but also the families and other caregivers who will struggle to afford their care, the authors warn. It’s these severe socioeconomic burdens, they wrote, that warrant “the attention of policymakers and stress the need for a mitigative action plan with particular focus on preparations to handle an increase in the prevalence of dementia.”

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