by Steve Macfarlane, The Conversation
PET scan of a human brain with Alzheimer’s disease. Credit: public domain
An article published this week in the journal Nature Medicine documents what is believed to be the first evidence that Alzheimer’s disease can be transmitted from person to person.
The finding arose from long-term follow up of patients who received human growth hormone (hGH) that was taken from brain tissue of deceased donors.
Preparations of donated hGH were used in medicine to treat a variety of conditions from 1959 onwards—including in Australia from the mid 60s.
The practice stopped in 1985 when it was discovered around 200 patients worldwide who had received these donations went on to develop Creuztfeldt-Jakob disease (CJD), which causes a rapidly progressive dementia. This is an otherwise extremely rare condition, affecting roughly one person in a million.
What’s CJD got to do with Alzheimer’s?
CJD is caused by prions: infective particles that are neither bacterial or viral, but consist of abnormally folded proteins that can be transmitted from cell to cell.
Other prion diseases include kuru, a dementia seen in New Guinea tribespeople caused by eating human tissue, scrapie (a disease of sheep) and variant CJD or bovine spongiform encephalopathy, otherwise known as mad cow disease. This raised public health concerns over the eating of beef products in the United Kingdom in the 1980s.
Human growth hormone used to come from donated organs
Human growth hormone (hGH) is produced in the brain by the pituitary gland. Treatments were originally prepared from purified human pituitary tissue.
But because the amount of hGH contained in a single gland is extremely small, any single dose given to any one patient could contain material from around 16,000 donated glands.
An average course of hGH treatment lasts around four years, so the chances of receiving contaminated material—even for a very rare condition such as CJD—became quite high for such people.
hGH is now manufactured synthetically in a laboratory, rather than from human tissue. So this particular mode of CJD transmission is no longer a risk.
What are the latest findings about Alzheimer’s disease?
The Nature Medicine paper provides the first evidence that transmission of Alzheimer’s disease can occur via human-to-human transmission.
The authors examined the outcomes of people who received donated hGH until 1985. They found five such recipients had developed early-onset Alzheimer’s disease.
They considered other explanations for the findings but concluded donated hGH was the likely cause.
Given Alzheimer’s disease is a much more common illness than CJD, the authors presume those who received donated hGH before 1985 may be at higher risk of developing Alzheimer’s disease.
Alzheimer’s disease is caused by presence of two abnormally folded proteins: amyloid and tau. There is increasing evidence these proteins spread in the brain in a similar way to prion diseases. So the mode of transmission the authors propose is certainly plausible.
However, given the amyloid protein deposits in the brain at least 20 years before clinical Alzheimer’s disease develops, there is likely to be a considerable time lag before cases that might arise from the receipt of donated hGH become evident.
More information: Gargi Banerjee et al, Iatrogenic Alzheimer’s disease in recipients of cadaveric pituitary-derived growth hormone, Nature Medicine (2024). DOI: 10.1038/s41591-023-02729-2
Journal information: Nature Medicine
Provided by The Conversation
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