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One of the strangest things that can make us sick – a misfolded protein that destroys the brain, called a prion – is even more frightening than we knew. The researchers were able to find the prions responsible for sporadic Creutzfeldt-Jakob disease (s-CJD), the most common prion disease in humans, seeded everywhere in the eyes of 11 patients.
The most recent results suggest that these universally fatal diseases, so rare, can be transmitted through the eyes. But they also indicate that our eyes could one day be used to spot these cases with less hassle than current test methods.
Prions can make us sick in many ways. Sometimes people are born with family mutations that increase the risk of developing prion disease, including some form of CJD. Most often, as in people with SJSC, prions appear spontaneously, normally harmless prion protein transforming into a misfolded form that also causes the folding of nearby proteins. But what is particularly terrifying about prions is that they can also be contagious, able to be passed from one person to another, or even from one animal to another.
It can take years, if not decades, for the symptoms of a prion disease (such as dementia or muscle weakness) to manifest, but once they manifest, it usually takes a few months before death.
The most infamous example of person-to-person transmission is kuru, a disease transmitted to the Fore tribe of Papua New Guinea through their ritual practice of eating the brains of deceased loved ones. (The kuru was eradicated when Fore family members stopped eating human meat in the 1960s). But they can also catch CJD with the help of contaminated surgical instruments that touch or approach the brain, as well as certain types of infected donor transplants.
Corneal grafting (partial or complete grafting of the cornea of the eye) is a type of graft suspected of spreading CJD, which has led scientists to believe that the eye is an important refuge for prions. Many people with CJD develop vision problems, which supports this theory. And some previous research has already found traces of prions in the retina and optic nerve.
But the researchers behind this latest study wanted to look for prions in the eye using another test method that has become the standard for prion detection in recent years, the RT-QuIC . Unlike older methods, RT-QuIC directly looks for the presence of misfolded prions in a sample using a fluorescent dye. And nowadays, the accuracy of the diagnostic test for CJD is greater than 90%.
They analyzed ocular tissue samples donated by 11 people who had died from sCJD. In all 11 people, the highest level of prions was seen in the retina. But the prions were also scattered in the cornea, lens and other muscles in and around the eye. According to the researchers, this is the first study to detect prions in these other parts of the eye.
The results, released Thursday in MBio, confirm the need for ophthalmologists to be particularly vigilant when treating people who may have CJD, according to lead author Christina Sigurdson, a pathologist for 39, University of California at San Diego.
"Surgeons could contaminate their instruments with prions without knowing it," she said in a statement.
The best way to prevent transmission would be for ophthalmologists to use single-use equipment, except that it requires intensive decontamination of these tools between uses, as prions can survive sterilization techniques that kill bacteria and viruses, such as radiation, formaldehyde. , and extreme heat (when used alone).
The study also encourages more to develop synthetic corneas, developed in the laboratory, which can be used instead for transplants. According to the researchers, there have been only two documented cases of MCJ probably caused by corneal transplants, but the procedure is gaining popularity around the world, thus increasing the very low but real risk of accidents. future.
Nevertheless, there are some points to remember from the study. The team found that the levels of prions in the retina were almost as high as they could find in the brain. This could mean that we can modify or create non-invasive tests for CJD that rely solely on the eye. In the current state of affairs, doctors usually diagnose CJD in a living person by testing their cerebrospinal fluid, which can only be obtained through an intensive, sometimes painful, spinal tap.
"This really suggests that we could develop an eye-based diagnostic test," Sigurdson said.
Sigurdson and his team are already trying to develop new diagnostic tests for prion diseases. They also hope to further explore the role of the eye in CJD, for example if a person's tears may carry prions.
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