Science behind the headlines: Breaking news stories
9 September 2015 - Discontinued hormone injections linked to the transmission of Alzheimer's disease
On 9 September, there were reports that injections of human growth hormone may be responsible for some people developing brain changes related to Alzheimer's disease. A small number of people who received this injection, which was discontinued in 1985, went on to develop a form of prion disease called iatrogenic Creutzfeldt-Jakob Disease (iCJD). This study investigated how else the injection may have affected their brain.
It is important to note that this research included just eight people and none of them were shown to have Alzheimer's disease. Four of the eight people did have widespread changes in their brain that are similar to changes seen in Alzheimer's.
There is no evidence that Alzheimer's disease can be transmitted from person to person, including via any current medical or dental procedures.
What was the injection and who received it?
The injection was of a hormone called human growth hormone and was given to people with short stature between 1958 and 1985. The hormone was made using parts of the brain from people who had previously died.
The use of the hormone was discontinued in 1985 when it was linked to the development of CJD in some people who had received it. In total, 77 of the 1,848 people in the UK who received the hormone have so far developed CJD.
How was this linked to Alzheimer's?
The researchers examined the brains of eight people who had developed CJD due to the human growth hormone injections. They found that four of these people had multiple clumps of a protein called amyloid spread throughout their brain, which is one of the hallmarks of Alzheimer's disease. Amyloid clumps do occur with natural ageing as well but would not normally be seen to this extent in people so young - the people in this study were between 36 and 51 when they died.
Whilst the people being studied had amyloid clumps present in their brain, it does not mean that they had Alzheimer's disease. They did not show changes in the other Alzheimer's-related protein, tau, and there was no clinical record of them having the symptoms of Alzheimer's disease. However, this could be due to the fact that they did not live long enough for these symptoms and processes to develop.
The researchers concluded that the presence of amyloid clumps found in these patients is likely to be due to the human growth hormone injection, as they also studied people affected by forms of CJD that were not caused by these injections and did not observe a substantial increase in amyloid clumps.
Does this mean that Alzheimer's can be transmitted from person to person?
No, this study does not show that Alzheimer's can be transmitted or that it is contagious. Whilst the people involved in the study did show changes related to Alzheimer's disease, there is no way to tell whether they would have gone on to develop the condition.
Other studies into medical procedures such as blood transfusions have not provided any evidence that Alzheimer's disease can be transmitted this way.
Whilst this study shows that the people who received injections of hormones or other treatments derived from the human brain in the past should be carefully monitored, it does not show that there is a risk for the general population.
Alzheimer's disease is caused by a complex interplay of genetic, lifestyle and environmental factors and there is no evidence that it can be caught from another person.
For more information on CJD transmitted via human growth hormone injections, see the iatrogenic CJD section on the NHS choices website.