Forebrain atrophy in early AD, by Masters et al, page-16

That is an interesting question Scott. What exactly causes areas of the brain to shrink? Cell death, prevention of new cell growth or just a reduction in size of all neurons or other. If I had to guess I think, as removal of iron improves the situation, it will be something that protects the neuron, binding to the excess iron, becoming ineffective.
I remember more than a decade ago U of Rio published that the anticancer component P53 would bind to iron in sheets and become useless. P53 is responsible for cell/DNA repair and cell destruction where it can't be repaired. Normal cells, not neurons. Maybe something similar in neurons. That is just a wild guess.