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Eyes offer window into fatal prion disease

US researchers have identified infectious proteins that cause the spread of prion disease throughout the eyes, potentially opening the door for new ways to diagnose and treat the incurable condition.

The study is the first to discover that the fatal disease can be detected in parts of the eye other than the retina and optic nerve. The infectious proteins were found in the eyes of 11 patients suffering from the progressive neurodegenerative disorder.

University of California-San Diego researchers studied the eyes of people with sporadic Creutzfeldt-Jakob disease (CJD), which is the most common and well-known prion disorder. They discovered prion seeds – the infectious proteins that cause the disease – spread throughout the eyes of all the patients.

About 40% of CJD patients develop eye-related issues, with vision problems being the first symptom in some patients. This prompted pathologist and study co-author Professor Christina Sigurdson to lead an investigation linking ocular changes with the disease.

In each patient, the highest levels of prion seeds were in the retina. They were also detected in the cornea, optic nerve, lens, sclera and ciliary muscles. Previous studies have found prions in patients’ retinas and optic nerves, but this was the first time they had been found elsewhere in the eye.

“It really suggests we could develop a diagnostic, eye-based assay. Future eye-based tests may be useful to monitor disease progression and evaluate new treatments,” Sigurdson said.

Prions are misfolded proteins that can emerge spontaneously in the brain, causing neurons to die. CJD patients’ cognitive decline is comparable to patients with Parkinson’s and Alzheimer’s disease, which also involve abnormal accumulation of proteins in the brain.

Unlike Parkinson’s and Alzheimer’s, however, prion diseases accelerate rapidly, with the majority of patients dead within a year of diagnosis. About 350 people are diagnosed with the disease every year, with symptoms starting around 60 years old.

According to Sigurdson, two case studies have also found prions could be transmitted through contaminated equipment used in corneal transplant procedures, suggesting surgeons should be cautious and consider implementing single-use tools into their clinic.

Senior co-author Dr Michael Geschwind believed the research could have applications in other diseases.

“If this method can be used to amplify other aggregated proteins, this might lead to advances in diagnosis for Alzheimer’s, Parkinson’s and related diseases,” he said.

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