A study in the journal "Nature" provides new evidence that certain medical procedures can transmit the "seeds" of Alzheimer's disease.

Since 1985, treatments for short stature have used synthetic human growth hormone, in part because batches derived from human pituitary glands can transmit prion diseases like Creutzfeldt–Jakob (CJD).

Prion diseases arise from proteins that cause other proteins to misfold. CJD, the prion disease that most commonly affects humans, can be inherited or acquired through a surgical procedure such as a cornea transplant.

The 2015 study examined eight patients who have acquired CJD via growth hormone harvested from human cadavers prior to the 1985 switch to synthetics.

Four subjects also showed signs of amyloid-β protein deposits, which suggested such a procedure could transmit Alzheimer's disease as well.

When John Collinge of University College London tracked down the original human hormone batches and injected them into special mice, he and his colleagues confirmed such transmission could occur.

"I was rather amazed that we could seed so easily from this material, which had sat around at room temperature as a dry powder for 30 or 40 years," he said.

Collinge emphasized none of these diseases is contagious, merely transmissible.

"You can't catch any of these diseases by contact, including intimate contact, with a carer or a loved one with Alzheimer's disease. It's very important that we don't scare people."