Alzheimer’s disease may have once spread from person to person, but the risk of this happening today is incredibly low.

An article published this week in the journal Natural medicine documents what is considered the first evidence that Alzheimer’s disease can be passed from person to person.

This discovery is the result of long-term follow-up of patients who received human growth hormone (hGH) taken from the brain tissue of deceased donors.

Donated preparations of hGH were used medicinally to treat various conditions from 1959 onwards, notably in Australia from the mid-1960s.

This practice stopped in 1985 when it was discovered that around 200 patients worldwide who had received these donations had developed Creuztfeldt-Jakob disease (CJD), which causes rapidly progressive dementia. It is an extremely rare disease that affects around one in a million people.

What is the relationship between CJD and Alzheimer’s disease?

CJD is caused by prions: infectious particles that are neither bacterial nor viral, but made of abnormally folded proteins that can be transmitted from cell to cell.

Other prion diseases include kuru, a dementia seen in New Guinea tribesmen caused by eating human tissue, scrapie (a disease of sheep), and variant CJD or bovine spongiform encephalopathy, also known as mad cow disease. This raised public health concerns over the consumption of beef products in the UK in the 1980s.

Human growth hormone came from organ donations

Human growth hormone (hGH) is produced in the brain by the pituitary gland. The treatments were initially 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 a patient may contain material from approximately 16,000 given glands.

An average hGH treatment lasts about four years, so the chances of receiving contaminated material – even for a very rare disease such as CJD – have become quite high for these people.

HGH is now made synthetically in the laboratory, rather than from human tissue. This particular mode of transmission of CJD therefore no longer presents a risk.

What are the latest discoveries about Alzheimer’s disease?

THE Natural medicine The paper provides the first evidence that transmission of Alzheimer’s disease can occur via human-to-human transmission.

The authors looked at the outcomes of people who received hGH donations through 1985. They found that five of these recipients developed early-stage Alzheimer’s disease.

They considered other explanations for these results, but concluded that hGH donation was the likely cause.

Since Alzheimer’s disease is a much more common disease than CJD, the authors speculate that those who received hGH donation before 1985 may be at higher risk of developing Alzheimer’s disease.

Alzheimer’s disease is caused by the presence of two abnormally folded proteins: amyloid and tau. There is growing evidence that these proteins spread in the brain in a similar way to prion diseases. The mode of transmission proposed by the authors is therefore certainly plausible.

However, given amyloid protein deposits in the brain at least 20 years before the clinical development of Alzheimer’s disease, it will likely take a considerable period of time before cases that may result from receipt of hGH donation become obvious.

When was this process used in Australia?

In Australia, donated pituitary material was used from 1967 to 1985 to treat short and infertile people.

More than 2,000 people have benefited from such treatment. Four developed CJD, the last case identified in 1991. All four cases were likely linked to a single contaminated batch.

The chances of further cases of CJD developing in recipients of pituitary material today, long after the last identified case in Australia, are considered incredibly low.

Young-onset Alzheimer’s disease (defined as occurring before age 65) is rare, accounting for approximately 5% of all cases. Below 50 years of age, it is rare and it is likely that there is a genetic contribution.

The risk is very low and you cannot catch it like a virus.

THE Natural medicine The article identified five cases diagnosed in people aged 38 to 55. This is more than one would expect by chance, but it is still very low compared to the total number of patients treated worldwide.

Although the long “incubation period” of Alzheimer’s disease may allow more similar cases to be identified in the future, the absolute risk remains very low. The main scientific interest of the article is that it is the first to demonstrate that Alzheimer’s disease can be transmitted from person to person in the same way as prion diseases, rather than present a risk to public health.

The authors were keen to emphasize, as I will, that Alzheimer’s disease cannot be contracted through contact with or providing care to people with Alzheimer’s disease.

This article is republished from The Conversation under a Creative Commons license. Read the original article.