Alzheimer’s may have formerly spread from person to person, but the likelihood of doing so today is extremely low

An article published this week in the journal Nature Medicine presents what is thought to be the first proof that Alzheimer’s disease can be passed from person to person.

The discovery came from a long-term study of patients who received human growth hormone (hGH) extracted from the brain tissue of deceased donors.

Donated human growth hormone preparations were utilized in medicine to treat a number of ailments beginning in 1959, notably in Australia in the mid-1960s.

The procedure was discontinued in 1985 after it was determined that approximately 200 patients worldwide who received these donations went on to acquire Creuztfeldt-Jakob disease (CJD), a fast-progressive dementia. This is an incredibly rare disorder that affects around one person in a million.

What does CJD have to do with Alzheimer’s?

CJD is caused by prions, which are infective particles made up of improperly folded proteins that can be passed from cell to cell.

Other prion disorders include kuru, a dementia caused by consuming human tissue among New Guinea tribespeople, scrapie (a sheep disease), and variant CJD, sometimes known as mad cow disease. This created public health worries about the consumption of beef products in the United Kingdom during the 1980s.

Human growth hormone used to be derived from donated organs

The pituitary gland, located in the brain, produces human growth hormone (hGH). Treatments were initially created from purified human pituitary tissue.

However, because the amount of hGH contained in a single gland is so small, any one dose administered to a patient could comprise material from approximately 16,000 donated glands.

An average course of hGH treatment lasts about four years; therefore, the chances of acquiring tainted material—even for a very rare disorder like CJD—have increased significantly for such persons.

hGH is currently synthesized in a laboratory rather than derived from human tissue. As a result, this route of CJD transmission is no longer considered risky.

What are the most recent results about Alzheimer’s disease?

The Nature Medicine research presents the first proof that Alzheimer’s disease can be transmitted from person to person.

The authors looked at the results of people who received donated human growth hormones up until 1985. They discovered that five of these individuals had developed early-onset Alzheimer’s disease.

They examined alternative reasons for the findings but decided that donated hGH was the most likely cause.

Given that Alzheimer’s disease is a considerably more frequent illness than CJD, the authors believe that people who received donated hGH before to 1985 are more likely to get Alzheimer’s disease.

Alzheimer’s disease is caused by the presence of two improperly folded proteins, amyloid and tau. There is mounting evidence that these proteins propagate in the brain in a manner similar to prion disorders. So, the authors’ proposed route of transmission is probably possible.

However, considering that amyloid protein deposits in the brain occur at least 20 years before clinical Alzheimer’s disease occurs, there is likely to be a significant time lag before instances resulting from the administration of donated hGH become apparent.

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

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