Five people appear to have developed Alzheimer’s disease after receiving growth hormones from deceased donors’ brains as children. Although based on a small group of people, this suggests that the condition could theoretically be transmitted during medical procedures. However, measures are in place to prevent this. One expert has also pointed out that this study doesn’t definitively prove that these recipients developed Alzheimer’s in this way.

From the late 1950s until 1985, children around the world with growth issues received injections of human growth hormone, derived from the pituitary gland in the brains of donor cadavers. In the UK, more than 1800 children received this treatment, while around 7700 children did so in the US.

The approach was banned globally when it came to light that some recipients died from a rare condition called Creutzfeldt-Jakob disease after receiving hormones contaminated with misfolded proteins called prions. These cause progressive and irreparable damage to the brain and nervous system by clumping together and making other proteins misfold.

Now, Gargi Banerjee at University College London and her colleagues have uncovered a handful of other people who may have developed Alzheimer’s disease from these treatments. Similar to prion-related conditions, a key characteristic of Alzheimer’s is the abnormal build-up of two misfolded proteins in the brain: amyloid-beta and tau.

As part of the UK’s National Prion Monitoring Cohort, the team reviewed eight cases where people received batches of donated human growth hormones as children that were later discovered to contain traces of misfolded amyloid-beta.

Of these eight, seven reported cognitive issues in their 40s and 50s. Three of them were diagnosed with Alzheimer’s disease, while two met the diagnostic criteria for the condition after reporting symptoms such as memory loss and difficulty concentrating. Another two experienced cognitive impairment, while the eighth person had no symptoms, but showed signs of Alzheimer’s in brain scans. Of the group, six survive.

All the recipients bar one, who only self-reported having cognitive impairment, had elevated levels of misfolded amyloid-beta and tau in their brains.

In another part of their study, the researchers analysed the DNA of five of the recipients, the only ones with samples available, and found that none had a heightened genetic risk of any neurodegenerative condition, suggesting that their symptoms weren’t inherited.

Writing in their paper, the researchers say there could be alternative explanations for the findings. For example, two of the individuals had an intellectual disability, which has been linked to a heightened risk of dementia, and the recipients’ initial growth issues may have led to cognitive impairments. But based on the fact that few people have developed early-onset Alzheimer’s disease after receiving uncontaminated growth hormones, the team concludes that contaminated injections are the most plausible cause.

“It’s important to recognise that this very rare, acquired form of Alzheimer’s disease exists, so that people treated with cadaveric growth hormone can get help and support should they need it,” says Banerjee. “There is no suggestion that Alzheimer’s disease can be transmitted between people during close contact, or by caring for people with Alzheimer’s disease, or via routine medical care.”

The researchers write that the results “should prompt both further consideration of public health implications and the primary prevention of [transmissible] Alzheimer’s disease – for example, by ensuring effective decontamination of surgical instruments”, which is already routinely done.

They are now working with the UK Health Security Agency and the Department of Health and Social Care to determine how many people who received these hormone injections may be at risk.

Lawrence Honig at Columbia University in New York says that the study doesn’t prove that Alzheimer’s was due to these injections. “There were apparently about 2000 persons who received these HGH [human growth hormone] preparations in the UK, and Alzheimer’s disease biomarker and pathological changes in the 50s are not extraordinarily uncommon, so an association, or causative association, from the injections cannot be certain,” he says.