On January 29, a new report from Nature Medicine stated that in five people who received contaminated injections of a growth hormone as children, researchers found that they developed Alzheimer’s disease unusually early. While this may sound the alarm, scientists are quick to emphasize that Alzheimer’s is not contagious in everyday settings.
“We are not suggesting for a moment that you can catch Alzheimer’s disease,” said John Collinge of the University College London’s Institute of Prion Diseases. “This is not transmissible in the sense of a viral or bacterial infection.”
Alzheimer’s disease normally presents itself spontaneously in older individuals. In the United States, one in nine people ages 65 and older have the disease. This statistic is what made the newly described cases so interesting to researchers. Symptoms in these five people began to present between the ages of 38 and 55. When looking at the genetic data of three of the patients, researchers could not find mutations indicating a cause for early-onset forms of the disease.
However, the individuals in the study had all received growth hormone injections when they were younger to treat various growth disorders. The growth hormones that they took were extracted from the pituitary glands of cadavers and combined into batches; today, this method is no longer used. It was found that some of the mixtures were contaminated with prions, an infectious and malformed protein that caused a disease called Creutzfeldt-Jakob disease. Due to this method of extracting growth hormones, more than 200 people were affected by this disease, and the treatment was stopped in 1985. Today, doctors use synthetic versions.
For the people who did take the contaminated growth hormone, though, the batches held another problem. In an earlier experiment, Collinge and his colleagues found higher-than-average levels of amyloid-beta, a protein that aids in neurophysiological function, in four people who died of Creutzfeldt-Jakob disease. Accumulation of amyloid-beta protein is a key sign of Alzheimer’s, and sends many researchers into question about whether some of the protein was transferred along with the prions that caused Creutzfeldt-Jakob disease.
Now, researchers have eight more patients who received contaminated growth hormone to compare results and do more clinical studies. While none of the people had Creutzfeldt-Jakob disease, three had already received an Alzheimer’s diagnosis. Further exams show that two individuals show signs of cognitive trouble. The most likely cause of Alzheimer’s appearing so early is the introduction of the amyloid-beta protein early in life.
It is important to note that it is unlikely for someone to have Alzheimer’s due to growth hormones today due to the change to synthetic injections. Beyond these rare circumstances, the studies may hold information regarding how Alzheimer’s disease can take hold in the brain and whether impacted amyloid-beta protein, like a prion, causes other versions of the protein to misfold. “Untangling the details of how various forms of A-beta spread lies ahead,” Collinge said. “A great deal more research needs to be done.”
