The Generative Brain

MRC Prion Unit direct detection assay (solid-state capture and immunodetection of disease-associated PrP in blood and urine)

The direct detection assay (DDA) is a non-amplification prion test built at the MRC Prion Unit at UCL. It captures disease-associated prion protein from whole blood on a steel powder matrix and then detects it with antibodies, without protease digestion. It was first reported in The Lancet in February 2011 as a prototype blood test for variant CJD: in a masked panel of 190 bloods it flagged 15 of 21 vCJD samples and no others, giving 71.4 percent sensitivity and 100 percent specificity. A 2014 study on 5000 US donor samples and other panels found no false positives in donors and proposed a UK blood prevalence study, and in 2016 the method was adapted to urine, detecting 40 percent of sporadic CJD cases but only 1 of 13 vCJD cases. The test was used at the National Prion Clinic for diagnosis, but by search excerpt the clinic no longer offers it routinely and the MRC funding programme behind it closed in 2016. Information only, not medical advice.

Key facts

  • The assay dilutes blood or urine in a buffer with albumin and CHAPS detergent, binds abnormal PrP to steel particles (AISI 304 steel for blood, AISI 316 for urine), washes, and detects the bound protein with ICSM monoclonal antibodies, with no protease or guanidine step.
  • It works on whole blood so abnormal PrP is captured whatever blood fraction it sits in, and its readout is chemiluminescence scored against a cut-off of the uninfected mean plus 3 standard deviations.
  • In the Lancet 2011 study, the assay told apart a 10^-10 dilution of vCJD brain from a 10^-6 dilution of normal brain, and in a masked panel of 190 whole blood samples (21 vCJD, 27 sporadic CJD, 42 other neurological disease, 100 normal) it was positive in 15 samples, all vCJD: sensitivity 71.4 percent (95% CI 47.8 to 88.7), specificity 100 percent (95% CI 97.8 to 100). The work was MRC funded.
  • The 2014 JAMA Neurology study found no positives among 5000 presumed negative US blood donors (specificity 95% CI 99.93 to 100), 200 healthy UK donors or 352 non-prion neurodegenerative patients; 2 of 105 likely prion disease patients with sporadic CJD were reactive, and sensitivity in a small blind vCJD panel was 70 percent (95% CI 34.8 to 93.3).
  • The authors said this specificity justified screening a large UK population sample and at-risk groups to estimate prion levels in UK blood donors, to inform whether donations need routine vCJD screening.
  • A blood prevalence study comparing 20,000 UK samples with 20,000 US samples, with John Collinge as contact, received a favourable ethics opinion on 25 November 2013; no results have been found.
  • A 2014 case report described a UK vCJD patient with typical clinical features whose DDA blood test was negative and whose lymphoreticular tissue held very little abnormal PrP, so a negative blood or tonsil test does not rule out vCJD and prevalence estimates may be affected.
  • In the 2016 urine adaptation, 162 anonymised samples were tested: no false positives in 125 controls, sensitivity 40 percent for sporadic CJD (95% CI 19 to 64) and 7.7 percent (1 of 13) for vCJD; the authors called it the first detection of a disease-related prion analyte outside the central nervous system.
  • In mice infected with RML prions the DDA detected abnormal PrP in blood from 20 days after inoculation, long before clinical disease, but the signal did not track blood infectivity.
  • The 2015 paper said the vCJD blood test was in clinical use for diagnosis of prion disease, and the UCL REF2014 case study said about 115 patients had been tested through the National Prion Clinic, describing use as both evaluative and routine.
  • The method is patented by D-Gen Ltd with Jackson, Collinge and Edgeworth as inventors (priority 16 September 2010); the US patent granted in May 2019 is listed by Google Patents as expired for unpaid fees, and two authors declared D-Gen shareholdings in 2015.
  • By search excerpt only, the National Prion Clinic says it no longer routinely offers the vCJD blood test (DDA) and asks clinicians to discuss cases first; a 2022 Inquiry statement by Simon Mead is reported to say the MRC closed the programme funding the blood test at its 2016 review and that the case for a vCJD screening blood test is now weaker than in 2014.

Timeline

  1. 2010Priority date of the D-Gen patent on steel capture assay for prions.
  2. 2011Lancet publishes the prototype vCJD blood test (15 of 21 vCJD, 100 percent specificity).
  3. 2012PCT patent application PCT/GB2011/001341 published.
  4. 2013Favourable ethics opinion for the 20,000 versus 20,000 vCJD blood prevalence study.
  5. 2014Blood letter on a highly specific blood test for vCJD.
  6. 2014JAMA Neurology case report of DDA-negative vCJD; population screening accuracy study published online (print April 2014).
  7. 2014Government response to the Commons committee says it will explore a prevalence study using the MRC Prion Unit test but cites hurdles (search excerpt).
  8. 2015Mouse study shows preclinical detection of abnormal PrP in blood.
  9. 2016MRC quinquennial review reported to close the blood test funding programme (search excerpt).
  10. 2016JAMA Neurology urine adaptation for sporadic CJD (print issue).
  11. 2019US patent US10288627B2 granted.
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