New blood test for prion disease looks promising
Written by Catharine Paddock PhD
Scientists have developed an accurate biochemical test that detects prions in the blood of patients with variant Creutzfeldt-Jakob disease. If validated, it could lead to a valuable tool for pre-symptom diagnosis of the disease and screening of donated blood supply.
The team – led by senior author Claudio Soto, professor of neurology at the University of Texas Health Science Center at Houston (UTHealth) Medical School – reports the work in the journal Science Translational Medicine.
The new study follows the publication of earlier research in 2014 where, after years of work, Prof. Soto and colleagues describe how they detected prions in urine.
Human prion diseases – including the sporadic and variant forms of Creutzfeldt-Jakob disease (CJD and vCJD) – are infectious and invariably fatal conditions that can cause progressive degeneration or the death of nerve cells or neurons.
The annual worldwide rate of CJD is around 1 new case per million of the population.
The much rarer vCJD is a new disease that was first described in 1996 in the United Kingdom. It is thought to arise in people who either ate meat from cattle infected with bovine spongiform encephalopathy (BSE or mad cow disease), or received blood transfusions from infected donors who did not have any symptoms.
Currently no definitive diagnostic test for vCJD
Worldwide, more than 220 cases of vCJD have been reported, most of them in the U.K. Four cases have been reported in the United States, with infection likely to have occurred outside the U.S.
The disease is caused by misfolded infectious proteins called prions that gradually build up and cause damage for decades before symptoms emerge.
On average, people infected with vCJD die 2 years after emergence of symptoms. At first, these include hallucinations and mood disorders such as depression and anxiety, which can be attributed to other conditions. Later, the symptoms can progress to more severe dementia, muscle spasms, and loss of coordination.
Prof. Soto and colleagues note that there is currently no definitive diagnostic test for vCJD that can help distinguish it from other disorders with similar symptoms, and neither is there a validated screen to detect prions in donated blood.
Prion test showed ‘100 percent sensitivity and specificity’
For the new study, the team analyzed blood samples from 14 patients diagnosed with vCJD and 153 controls. The controls included patients with sporadic CJD and other brain conditions – such as dementia, Parkinson’s disease, brain injury, stroke, and epilepsy- and 49 healthy individuals.
To detect the vCJD prions, the team used a new tool called “a protein misfolding cyclic amplification assay” (PMCA). Developed in Prof. Soto’s laboratory, the tool mimics the prion replication that occurs in prion disease in the brain.
The results show that the PMCA tool detected prions “with 100 percent sensitivity and specificity in blood samples from vCJD patients.”
Sensitivity is the extent to which a negative result rules out disease, and specificity is the extent to which a positive result rules it in.
The researchers note that further studies are now needed to validate the new technology. Once they do, the new test could be used for the noninvasive diagnosis of vCJD before symptoms emerge and to screen blood supplies for prion contamination.