A possibility has been raised that brain proteins that cause dementia or cerebral hemorrhage could be transmitted to other people through blood transfusions. There is still no conclusive evidence that transfusions spread dementia, but some said a preemptive response is needed—like the past measures that blocked the protein that causes mad cow disease—to prevent potential risks.
A team led by John Collinge at University College London (UCL) said in The Lancet on the 22nd that "to ensure the safety of blood transfusions, we need to investigate the transmissibility of Alzheimer's dementia and cerebral amyloid angiopathy (CAA) through amyloid beta protein."
Amyloid beta is originally a protein that protects nerve cells, but when it detaches from cells and aggregates, it damages nerve cells and causes dementia. Cerebral amyloid angiopathy is a disease in which amyloid beta protein builds up in brain blood vessels, causing damage and leading to cerebral hemorrhage.
◇ Onset after receiving a transfusion or tissue transplant
This paper is not new evidence of the transmissibility of dementia and cerebral amyloid angiopathy, but a review analyzing existing related studies. Collinge's team said, "To ensure that transfusions, which save many lives, are safe, we need to thoroughly investigate potential risks."
According to the researchers, a 2023 study of about 1 million people in Sweden and Denmark found that people who received blood transfusions from donors who had CAA with cerebral hemorrhage faced a higher risk of experiencing cerebral hemorrhage.
Cases also appeared in which people developed angiopathy after receiving tissue from cadavers. In 2020, a UCL team reported cases in which people who, in childhood, received transplants of the dura mater—the membrane covering the brain and spinal cord—from cadavers suffered cerebral hemorrhage due to CAA 30 to 40 years later.
The possibility of dementia transmission was also raised. In 2024, Collinge reported five patients who, decades after receiving growth hormone extracted from cadaveric pituitary glands in childhood, developed Alzheimer's disease. Early this year, he reported that a patient who, in childhood, received cadaver-derived growth hormone and showed early dementia symptoms was confirmed as having Alzheimer's disease in a postmortem examination.
Fortunately, the medical use of cadaveric dura mater and growth hormone is already banned. That leaves the potential transmission of amyloid beta protein through future blood transfusions as the concern. Collinge said a preemptive response is needed, like the earlier response that used blood screening to address variant Creutzfeldt-Jakob disease (vCJD).
vCJD is a fatal degenerative brain disease in which abnormal prion proteins accumulate and the brain develops sponge-like holes. It was originally a disease that affected cattle and spread to people through meat, and was also called human mad cow disease. Cattle with the disease staggered due to loss of balance or showed aggressive behavior.
◇ "We should test blood vs. excessive fear"
In the United Kingdom, 1,848 people received growth hormone extracted from cadaveric pituitary glands from 1959 to 1985. After some received growth hormone contaminated with abnormal prions and died of vCJD, all related products were recalled and the treatment was halted.
Collinge said, "At the time of the vCJD outbreak, the measure to filter leukocytes—which concentrate prions—from blood for transfusions to prevent risk was taken based on the principle that 'the absence of evidence of harm is not evidence of absence of harm,'" adding, "This contrasted with HIV and hepatitis C, where responses were delayed as scientists sought clearer evidence."
Scientists worried that this study could trigger excessive fear of transfusions. Susan Kohlhaas of Alzheimer's Research UK said, "As the authors argue, we need studies to confirm whether transmission through blood actually occurs, who is at greater risk, and whether measures are needed to reduce the risk," while adding, "The important point is that this does not mean Alzheimer's disease is contagious."
John Hardy of the UK Dementia Research Institute at UCL also said, "The risk of transmission of related diseases through tissues containing amyloid beta protein has been demonstrated," while adding, "Until a systematic investigation is conducted, the risk through transfusion is still not exactly known but is likely to be minimal."
Bart De Strooper of the same institute opposed measures such as prion testing. He countered, "Even the study cited as evidence of the possibility of amyloid beta transmission through blood products merely raised questions," adding, "It is premature to look for similarities with prions, and there is a risk of causing unnecessary public fear without evidence."
References
Lancet (2026), DOI: https://doi.org/10.1016/S0140-6736(26)00767-1
JAMA Neurology (2026), DOI: https://doi.org/10.1001/jamaneurol.2026.0437
Nature Medicine (2024), DOI: https://doi.org/10.1038/s41591-023-02729-2
JAMA (2023), DOI: https://doi.org/10.1001/jama.2023.14445