Sporadic CJD: research

What is the epidemiological and molecular baseline?

The 2026 Viruses review gives sporadic CJD about 85 percent of human prion disease cases, with a stable global incidence of 1 to 2 per million per year. Subtypes are defined by codon 129 genotype combined with the electrophoretic type of protease-resistant prion protein, and the review lists MM1, MM2-cortical, MM2-thalamic, MV1, MV2, VV1 and VV2, naming MM1 as the most common and giving VV2 as about 15 percent of sporadic cases. Those subtypes are treated separately in sporadic CJD subtypes.

Why has every completed trial been uninformative?

The seven completed human studies catalogued by cureffi.org, covering flupirtine in Germany, pentosan polysulphate in the United Kingdom and Japan, quinacrine in France, the United Kingdom and the United States, and doxycycline in France and Italy, recruited only symptomatic people and were mostly sporadic CJD patients. The two nominally positive results, pentosan polysulphate in the United Kingdom and PRION-1, are attributed in that account to confounders, and the three randomised studies, flupirtine with 28 participants, quinacrine with 54 and doxycycline with 121, did not establish benefit.

The structural problem identified there is the endpoint. Survival in sporadic CJD varies with sex, age, subtype and codon 129 genotype, so a survival comparison across a heterogeneous group is confounded; stratifying leaves subgroups too small to analyse. The doxycycline trial was powered only to detect a two-fold increase in one-year survival. The 2026 Viruses review states that no approved therapy alters the course of prion disease, that management is symptomatic and palliative, and that quinacrine failed to show sustained benefit in both the randomised trial and the PRION-1 cohort.

What is the evidence for SERPINA3 as a target?

Vanni and colleagues measured SERPINA3 in 128 human post-mortem frontal cortex samples. Messenger RNA was about 40 times control levels in sporadic CJD, 39 times in genetic and in variant CJD, 53 times in fatal familial insomnia and 347 times in iatrogenic CJD, against about 7 times in Alzheimer disease, with the authors noting the Alzheimer figure may be overestimated because their Alzheimer group was older than the available controls. Protein was about six times control levels by Western blot, with lower molecular weight bands appearing only in prion-infected samples. Staining was found in most residual cortical neurons and many reactive astrocytes, concentrated in cell bodies and apical dendrites of pyramidal neurons, and prion protein deposits themselves were not stained.

Zattoni and colleagues then asked whether any other serpin behaved the same way. Of 41 human serpin genes, nine were analysable in frontal cortex; of 71 mouse serpins, 14. SERPINA3 rose about 54-fold in human sporadic CJD cortex and about 32.7-fold in early Alzheimer cortex, and the mouse ortholog SerpinA3n was the only serpin raised in both mouse models. SERPINB1 rose in both human groups but not significantly in either mouse model. In cell experiments, SerpinA3n increased prion accumulation and reducing it lowered prion load. The authors propose SERPINA3 as a potential therapeutic target while stating that its role in neurodegeneration remains unclear.

The attempt to act on it has stalled at pharmacokinetics. Colini Baldeschi and colleagues identified compound 5, ARN1468, which inhibits SERPINA3 and SerpinA3n and reduced prion load in chronically infected cells, and report that low bioavailability prevented in vivo studies in prion-infected mice.

What is the microglial GPNMB work?

Caredio and colleagues, reporting in Nature Communications in 2026, describe a microglial state in terminally sick prion-infected mice marked by high Gpnmb expression together with phagocytic and lysosomal gene signatures, concentrated in regions with heavy cell death. They report that soluble factors released by dying cells, rather than protein aggregates, drive this state, and propose Gpnmb-positive microglia as a phagocytic response linking cell loss to microglial activation. The preprint version reported raised GPNMB in cerebrospinal fluid from sporadic CJD patients, and knocking out Gpnmb reduced clearance of apoptotic cells in BV2 cells and human induced pluripotent stem cell derived microglia.

The human component is five sporadic CJD patients against five matched controls. That is too small to support a diagnostic or prognostic claim, and GPNMB is also under development as a pharmacodynamic marker of PIKfyve inhibition in amyotrophic lateral sclerosis, so a raised value does not indicate prion disease. The grant-stage work extending this is described in CJD research.

Where did the anti-prion compound work reach?

Masone and colleagues tested Zn(II)-BnPyP, a zinc-containing tetracationic porphyrin, with a proposed two-part mechanism: binding at the C-terminal globular domain lowers the melting temperature of recombinant human prion protein by about 5 degrees and opens the conformation, while zinc-mediated coordination of octapeptide repeat histidines triggers clathrin-dependent endocytosis and lysosomal degradation of cell-surface prion protein.

Strain breadth was tested in protein misfolding cyclic amplification with variant CJD, sporadic CJD of the VV2 subtype, classical scrapie and a bank vole prion generated de novo, and in ScN2a cells and cerebellar organotypic slices with the RML and 22L mouse strains. The compound inhibited amplification more effectively than Fe(III)-TMPyP without depleting cellular prion protein, with an IC50 of about 0.7 micromolar in cells, and cleared protease-resistant prion protein in slices at 1 to 2.5 micromolar.

The in vivo result was negative. Brain penetration was poor, with a brain-to-plasma ratio of 0.035; twelve weeks of intraperitoneal dosing at 10 mg per kg reached about 1.5 micromolar in brain with only about 20 percent reduction in cellular prion protein; and in RML-inoculated mice treatment from 40 days after inoculation did not change onset, at a median of 141.5 against 135 days, or terminal disease, at 153 against 152 days, in small groups of 6 and 9. The authors argue that acting on the precursor rather than on the misfolded form should be less prone to drug resistance, and state that this was not directly tested. Their listed limitations are insufficient brain exposure, failure of intraventricular delivery because of poor parenchymal diffusion, and the need for a more drug-like molecule.

Is there prion protein in the blood in sporadic disease?

Less than in variant CJD, and the evidence is thinner. Douet and colleagues found infectivity by bioassay in the plasma of 2 of 4 patients whose tests were positive for sporadic CJD, and in erythrocytes, leukocytes and plasma of one variant CJD patient, describing the levels as comparable to those reported in animals with transmissible spongiform encephalopathies. Concha-Marambio and colleagues used sporadic CJD patients as part of their 153-strong control group when reporting 100 percent sensitivity and specificity for variant CJD blood, which means their assay was configured to separate variant CJD from sporadic disease rather than to detect it.

A blood assay validated for sporadic CJD therefore does not yet exist. The 2026 biomarker position is set out in biomarkers, and the biosafety consequences in transmission and biosafety.

Which groups work on this?

The organisations active in the areas above include the Besta institute, the Danish Reference Center for Prion Diseases, the Lyon prion unit, INRAE Jouy-en-Josas, INRA-IHAP Toulouse, IRTA-CReSA, Saarland neuropathology, the UCSF Institute for Neurodegenerative Diseases, the University of Alberta centre and the Calgary prion research unit.