Pathological relationships involving iron and myelin may constitute a shared mechanism linking various rare and common brain diseases

Our genes may be affected by iron overloading in our brain, which can then influence future gene expression. These factors are believed to occur before clinical symptoms of many diseases appear:

"We therefore believe that, with respect to brain iron loading, this new model provides insights into early perturbations in molecular systems during a period corresponding to a pre-clinical disease stage in which compensatory responses are still sufficient to maintain the overall homeostasis of myelin and iron-related systems."

http://www.tandfonline.com/doi/abs/10.1080/21675511.2016.1198458#/doi/abs/10.1080/21675511.2016.1198458