New hope for a blood test for vCJD
British scientists have succeeded in developing a blood test for variant CJD (vCJD), the fatal neurodegenerative disease believed to have originated from cows. This is a major breakthrough as currently patients with suspected vCJD have to undergo a series of tests, including brain biopsy, to confirm diagnosis.
The new test, reported in today’s Lancet, developed by a team at the Medical Research Council’s Prion Unit working with the NHS National Prion Clinic in London, offers the possibility of earlier diagnosis for patients with vCJD and for screening donor blood.
Variant CJD is the human form of Bovine Spongiform Encephalopathy (BSE) or ‘mad cow’ disease which came to prominence in the UK in the late 1990’s during the BSE crisis. BSE is a prion disease that affects cows and causes the brain to develop a spongy texture due to the death of brain cells. BSE is able to jump species passing from cattle to humans through eating infected beef and beef products.
In the UK there have been around 200 deaths from vCJD. Much of the UK population born before 1996 (when rigorous measures to limit exposure to infected beef and beef products were put in place) have potentially been exposed to BSE‐contaminated food and it has been suggested that one in 4000 people could be carrying the infection without showing symptoms.
There is no treatment for vCJD and the diagnosis tends to be made at a very late stage when patients have developed symptoms associated with extensive damage to the brain. There are several reasons for this. The early symptoms of vCJD (such as anxiety, depression and tingling pains in the legs) are also symptomatic of other more common disorders so doctors understandably are more likely to attribute them to something less serious until symptoms such as difficulty with movement or balance and loss of mental abilities occur. At this stage, a more serious brain condition will be suspected but tests will be required to make the diagnosis and these take time to organise and interpret. vCJD typically progresses quite rapidly (over weeks and months) so the patient is likely to have advanced symptoms by the time a diagnosis is reached.
The new test is at an early (prototype) stage and when tried on 190 blood samples, of which 21 had vCJD, it picked up 15 of the samples with vCJD, giving a 71% success rate. Importantly, it did not produce any ‘false positives’ indicating that someone had vCJD when they did not.
Doctors involved in the work intend to begin using the new test on patients in their clinic immediately. However, more work is needed before the test can be used to screen healthy people who may be ‘silent’ carriers and to establish its potential use by the blood services to screen for silent vCJD in blood donors.
Early diagnosis is crucial for vCJD and for other rapidly progressing degenerative brain disease including the dementias, progressive supranclear palsy and multiple system atrophy. While effective treatments are yet to be developed, once they do become available, the sooner a treatment can be started, the better the chances are of a successful outcome. Earlier diagnosis also gives patients and their families more time to plan what they would like to do in the time left available to them.
You can find out more about the new blood test by visiting the National Prion Clinic website (www. prion.ucl. ac.uk).