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Prions found in skin of people with Creutzfeldt-Jakob disease

The brain of a patient who died from sporadic CJD (top) appears nearly identical to the brain of a mouse inoculated with infectious prions taken from the skin of patients who died from the disease (bottom). Case Western Reserve University

Creutzfeldt-Jakob disease (CJD) is one of many different types of human prion disease. Human prion diseases are brain diseases that cause dementia and other neurological symptoms. They are caused by normally harmless proteins that become misshapen, clump together, and accumulate in the brain. The accumulation of these clusters is associated with tissue damage that leaves sponge-like holes in the brain. Human prion diseases are difficult to diagnose, untreatable, and fatal.

Creutzfeldt-Jakob disease can occur sporadically or be inherited. Sporadic CJD is the most common human prion disease. It’s caused by the spontaneous transformation of normal prions into abnormal ones. Sporadic CJD affects an estimated one per million people worldwide each year.

While prion diseases are mostly associated with the brain, scientists have found abnormal infectious prion proteins in other organs, including the spleen, kidney, lungs, and liver. CJD is known to be transmissible by infected medical tools or tissues during invasive medical procedures, such as those involving the central nervous system and corneas. The potential for transmission via procedures that involve the skin remains unclear.

A research team led by Dr. Byron Caughey of NIH’s National Institute of Allergy and Infectious Diseases (NIAID) and Drs. Wenquan Zou and Qingzhong Kong at Case Western Reserve University School of Medicine tested for abnormal prion protein in the skin of people who died from CJD. They used a test called Real-Time Quaking-Induced Conversion (RT-QuIC) that was developed by Caughey’s group at NIAID’s Rocky Mountain Laboratories. Results were published on November 22, 2017, in Science Translational Medicine.

The scientists analyzed skin tissue samples from 38 patients—21 who had died from sporadic CJD, 2 from another form of CJD, and 15 who died of other causes. The samples came from the top of the head, near the ear, and the lower back. They also analyzed brain tissues.

RT-QuIC correctly detected abnormal prion protein in skin samples from every person with CJD but none in samples from the non-CJD group. However, no single skin location in the people with CJD always tested positive. Of the three skin areas, the area near the ear had the highest and most consistent activity in the RT-QuIC test (94%). Overall, activity in the skin samples of people with CJD was 1,000 to 100,000 times lower than in the brain tissue samples.

The scientists next inoculated "humanized" mice (engineered to make human prion proteins) with either brain or skin extracts from two of the people with sporadic CJD. All the mice developed prion disease and had brain degeneration and other symptoms. However, the disease took about twice as long (about 400 days) to develop in the mice receiving skin extracts.

“Perspective is important when interpreting these outcomes,” Caughey notes. “This study used humanized mice with tissue extracts directly inoculated into the brain, so the system was highly primed for infection. There is no evidence that transmission can occur in real-world situations via casual skin contact. However, the results raise transmission questions that warrant further study.” For example, certain medical procedures that involve the skin might pose some risk for transmission.

These findings suggest that RT-QuIC might be used with skin tissue samples as a diagnostic test for prion diseases. The scientists are now investigating when and where the pathological prion protein appears in skin, and how to inactivate its infectious forms.