杏吧原创

Alzheimer鈥檚 leads to a loss of brain tissue (Image: PASIEKA/Getty)

Can Alzheimer鈥檚 disease spread between people? Possibly, through a medical procedure banned in the 1980s 鈥� but some say the evidence is too circumstantial.

of University College London and his colleagues looked at the brains of eight people who had been injected with human growth hormone as children 鈥� a therapy that around 1800 people in the UK received between 1958 and 1985.

The hormone had been extracted from the pituitary glands of dead donors, but it later turned out that they had been harbouring the prion disease Creutzfeldt-Jakob Disease (CJD). The eight recipients contracted CJD, via the hormone, and later died.

Now, fresh autopsies on their brains have revealed that six also had amyloid plaques similar to those seen in Alzheimer鈥檚 鈥� even though they had died between the ages of 36 and 51, long before the disease typically develops.

Collinge believes molecules seeding the plaques were passed to the recipients via the donated growth hormone, saying the donors must have been developing Alzheimer鈥檚 as well as CJD.

Unexpected consequence?

The researchers confirmed that none of the six recipients carried known genes for developing early Alzheimer鈥檚, which might have explained the presence of the plaques. Nor could he find evidence of the Alzheimer鈥檚 amyloid protein in the brains of 116 additional people who died of CJD or other related diseases, but who didn鈥檛 receive contaminated growth hormone. This suggests that the appearance of amyloid plaques isn鈥檛 simply an unexpected consequence of developing CJD.

The team also found amyloid protein in the pituitary gland 鈥� where growth hormone is produced 鈥� of people who had died of Alzheimer鈥檚. This suggests that contamination is possible if growth hormone is extracted from the gland and then injected into a healthy recipient.

The good news is that it鈥檚 unlikely the disease can spread in blood, through transfusions for example, or through some common forms of surgery.

鈥淥ur current data have no bearing on dental surgery and certainly do not argue that dentistry poses a risk of Alzheimer鈥檚 disease, 鈥� says Collinge. 鈥淥ur findings might be relevant to some other medical or surgical procedures, but evaluating what risk there might be, if any, requires much further research. 鈥�

However, some researchers doubt that the new study even demonstrates that the growth hormone injections posed an Alzheimer鈥檚 risk. All six patients died of CJD so it wasn鈥檛 possible to say whether they would have gone on to develop Alzheimer鈥檚 if they hadn鈥檛 succumbed to the prion disease. Nor did any of them have signs of tau tangles, clumps of tau proteins that collect within brain cells and which are an important hallmark of Alzheimer鈥檚 disease.

What鈥檚 more, Collinge鈥檚 team couldn鈥檛 analyse samples of the growth hormone that was actually injected into the six patients to confirm whether it contained amyloid proteins.

Sceptical of a link

Because of this, David Irwin of the University of Pennsylvania in Philadelphia 鈥� 鈥� is sceptical of a link.

鈥淭here remains no definitive evidence that clinical manifestations of Alzheimer鈥檚 can be transmitted between humans,鈥� he says.

of the German Center for Neurodegenerative Diseases in T眉bingen, Germany, also has doubts. 鈥淲e have to make sure that it was really transmission,鈥� he says. The only proof, he says, could come from experiments in which any remaining samples of the contaminated hormone are injected into mice to see if the rodents develop Alzheimer鈥檚 plaques as well.

Collinge says these samples do indeed exist, and his team hopes to perform experiments along the lines of those suggested by Jucker soon. 鈥淏ut the experiments take one or two years,鈥� he says.

鈥淚f we know it was indeed transmission, we should start looking into other medical procedures where Alzheimer鈥檚 plaque material from the brain may come into contact with other patients,鈥� Jucker says.

Jucker has previously shown that it is possible to spread Alzheimer鈥檚 to mice by injecting human amyloid brain material into the brains of the rodents. Elsewhere this week, Jucker鈥檚 team reported that 鈥� at least a quarter of their lifespan 鈥� then regain their ability to cause disease. This suggests that if amyloid did somehow make it from one person鈥檚 brain to another鈥檚, it could potentially cause disease after very long incubation intervals.

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