The Generative Brain

Urine prion seed amplification (PMCA) test

Urine PMCA is a research laboratory method that looks for the misfolded prion protein (PrPSc) in urine by concentrating the sample and then amplifying any prion seeds through repeated rounds of protein misfolding cyclic amplification, with a Western blot readout. It was developed mainly by Claudio Soto's group in Houston with Fabio Moda of the Carlo Besta institute in Milan and the Cleveland prion surveillance center. In variant CJD it found prions in urine of 13 of 14 patients and in none of 224 others (NEJM, August 2014). A reworked version found prions in urine of 29 of 81 people with sporadic CJD (36 percent), mostly those with the VV subtypes, and in none of 160 controls (December 2023). It is also being tried on urine from carriers of the fatal familial insomnia mutation in the European ProFFIle project, with preliminary results only. No source opened describes it as a clinically available test. Information only, not medical advice.

Key facts

  • The method spins urine down at high speed (or, in the 2023 version, pulls prions out with iron oxide magnetic beads), adds the pellet to brain homogenate from mice that make human prion protein, and runs serial rounds of incubation and sonication before proteinase K digestion and Western blot; direct blotting of urine without amplification detects nothing.
  • In the 2014 study PrPSc was found in 13 of 14 people with variant CJD and in none of 224 others, giving a sensitivity of 92.9 percent (95 percent CI 66.1 to 99.8) and specificity of 100 percent; the wide interval reflects the small variant CJD group.
  • The same 2014 assay found no prions in urine from any of 68 people with sporadic CJD or 4 with genetic prion disease, and the authors estimated variant CJD urine holds only about 40 to 100 prion particles per ml.
  • The authors of the 2014 paper said further studies were needed before urine PrPSc detection could be used for diagnosis.
  • The 2023 version added magnetic extraction, extra chemical additives and substrates with either methionine or valine at codon 129, and found prions in 29 of 81 people with sporadic CJD and in none of 66 healthy and 94 neurological controls; the negative predictive value was 0.74.
  • Detection in sporadic CJD depended strongly on subtype: VV2 16 of 19, VV1 3 of 3, MV2 5 of 11, MM1 5 of 24, and none of 16 MM2 or 8 MV1 cases.
  • The 2023 authors propose urine testing as a possible non-invasive preliminary screen and suggest testing urine-derived medicines such as menopausal gonadotropin for prions; they are also exploring plasma.
  • Amplified variant CJD urine transmitted disease to humanised mice with the same strain features as variant CJD brain, while raw urine did not transmit (2019), and earlier bioassays found no detectable infectivity in raw urine from 3 sporadic CJD MM1 patients (2012).
  • The approach grew out of animal work: in 2008 the Soto group reported PMCA detection of infectious PrPSc in urine of about 80 percent of infected animals, and a separate 2008 bioassay found low infectivity in urine of scrapie-infected hamsters.
  • A different, non-amplification urine test from the MRC Prion Unit in London, adapted from its variant CJD blood assay, gave 40 percent sensitivity for sporadic CJD and 7.7 percent for variant CJD with 100 percent specificity (2016), the reverse pattern of the PMCA results.
  • In ProFFIle, PMCA and RT-QuIC detected FFI prions spiked into urine down to a 10 to the minus 12 dilution; 2 of 15 carrier urines were positive and all 17 control urines negative, results the team calls preliminary.
  • A Europe PMC title search shows no human prion urine paper after the 2023 study in its first 60 hits.

Timeline

  1. 2008Soto group reports PMCA detection of infectious prions in urine of infected animals (FEBS Letters, e-published 13 August 2008).
  2. 2008Bioassay shows low prion infectivity in urine of scrapie-infected hamsters.
  3. 2012Raw and concentrated urine from 3 sporadic CJD patients fails to transmit to humanised mice.
  4. 2014NEJM paper: prions in urine of 13 of 14 variant CJD patients, none of 224 others.
  5. 2016MRC Prion Unit reports a non-amplification urine immunoassay for sporadic CJD (JAMA Neurology).
  6. 2019PMCA-amplified variant CJD urine shown to keep infectivity and strain features in mice (e-published 26 March 2019).
  7. 2022ProFFIle project sheet lists optimising RT-QuIC and PMCA for urine and plasma of FFI carriers.
  8. 2023Sporadic CJD urine PMCA paper e-published (10 October 2023; print December 2023): 29 of 81 positive.
  9. 2024ProFFIle presents preliminary urine seeding results at the JPND symposium in Brussels (27 to 28 November 2024).
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