That is an interesting question Scott. What exactly causes areas...

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.