A group of scientists say they’ve made a surprising and potentially very important discovery in the brains of two people with Alzheimer’s disease: traces of a particular form of iron and copper deep inside deposits of amyloid plaque, a key marker of the fatal disease.

The regulation of these metals doesn’t seem to work so great in the brains of people with Alzheimer’s disease, though.

And some evidence has suggested that toxic forms of iron and copper can be found inside these plaques.

They then found elemental and metallic nanoparticles of iron and copper in the cores of these plaques, meaning that the elements had no oxidation—no electrons missing or added.

Beyond that, their exact origin is still a mystery, though past research from Telling’s team and others does suggest that amyloid plaques can trigger chemical reactions capable of converting less reactive forms of these elements into something more dangerous.