Alzheimer’s Disease May Be Transmissible in Certain Cases: Study

Findings provide first evidence Alzheimer’s could spread between humans via prion proteins.

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Alzheimer’s disease may be transmissible from one person to another, but not in the way you might think, a shocking new study suggests.

Scientists have identified several patients who likely contracted Alzheimer’s through a now-discontinued treatment involving human growth hormone extracted from cadaver brains. While the findings don’t mean Alzheimer’s can spread like the common cold, they provide the first evidence that under rare circumstances, the disease may be transmissible between humans.

Why Is the Hormone Treatment Banned?

The implications of the study, published on Jan. 29 in Nature Medicine, are far-reaching for both past and future Alzheimer’s research.

The now-banned human growth hormone procedure was once a common therapy for children with hormone deficiencies. Between 1959 and 1985, nearly 1,900 patients in the United Kingdom received cadaver-derived human growth hormone as treatment. Additionally, from 1963 to 1983, around 7,700 children in the United States and 27,000 children worldwide got the treatment.

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Globally, more than 200 cases of Creutzfeldt-Jakob disease have been linked to this procedure. Creutzfeldt–Jakob disease occurs when prions, a type of misfolded protein, trigger normal proteins in the brain to fold abnormally and cause damage. According to the U.S. Centers for Disease Control and Prevention, prion diseases such as Creutzfeldt–Jakob progress rapidly and are always fatal.

Synthetic human growth hormone has been used to treat growth issues for almost four decades.

“With the treatment not used since 1985, there is no cause for concern for the health of the general population,” Richard Oakley, associate director of research and innovation at the Alzheimer’s Society, said in a statement. “Nowadays, patients receive synthetic alternatives which have been approved for safety and do not pose a risk of transmitting diseases.”

Prion Proteins Blamed for Transmissible Alzheimer’s

The main culprits are prions, according to the study. Prions—proteins that trigger fatal neurodegenerative diseases by causing normal brain proteins to fold into abnormal shapes—act as seeds that cluster together to form the roots of long fibers, eventually becoming plaque. This process mirrors how amyloid-beta and tau proteins multiply and spread in the brains of Alzheimer’s patients.

Previously, researchers analyzed the brains of people who died from Creutzfeldt–Jakob disease after receiving the now-banned cadaver-derived human growth hormone treatment. While their brains showed markers of Alzheimer’s, it was unclear if the deceased had experienced symptoms. Separate research suggests Alzheimer’s could also spread through the same prion-seeding process, but the theory was unproven until now.

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In the new study, the researchers examined the brains of eight individuals who had received the cadaver-sourced hormone treatment but did not develop Creutzfeldt–Jakob disease. They had no family history of early-onset dementia or Alzheimer’s, the study noted.

Five of the eight patients showed signs of early-onset dementia, with symptoms starting between ages 38 and 55. Further analysis of the patients’ brains and spinal cords provided enough evidence to suggest two other patients could be diagnosed with Alzheimer’s disease.

The study notes this form of iatrogenic Alzheimer’s, caused by medical treatment such as the human growth hormone procedure, differs from sporadic and inherited Alzheimer’s. Patients with iatrogenic Alzheimer’s often experienced early onset disease, but their cognitive symptoms tended to progress slowly over a decade or more.

What Does It Mean for the General Population?

“While the new type of Alzheimer’s reported here is of great scientific interest, as it reveals a new way to spread the disease, there is no reason to fear it, as the way in which the disease was caused was stopped over 40 years ago,“ said Andrew Doig, a professor biochemistry at the University of Manchester and who specializes in Alzheimer’s disease. ”Disease transmission from human brain to brain in this way should never happen again.”

Because the disease could essentially be “passed” from one brain to another, the findings should spur further consideration of public health implications and prevention of iatrogenic Alzheimer’s disease. This could include more vigilant decontamination of surgical instruments, for example.

“It’s also important to stress that this is the only recorded instance of Alzheimer’s transmission between humans,“ said Susan Kohlhaas, executive director of research and partnerships at Alzheimer’s Research UK. ”There is no evidence to suggest that it can be passed through any other route, such as day-to-day activities or routine medical procedures.”

However, the study has revealed more about how amyloid fragments can propagate in the brain, providing new clues into Alzheimer’s progression and potential therapeutic targets, she added.