In that proper control of iron levels corresponds to healthy central nervous system function, a number of previous studies submit that iron deficiency is associated with cognitive impairment, whereas iron overload may promote neurodegenerative diseases.  Neda Jahanshad , from University of California/Los Angeles (UCLA; California, USA), conducted brain MRI scans on 615 healthy young-adult twins and siblings, average age 23 years. Of these, 574 were also given an additional brain scan that measured the brains myelin connections and their integrity. As well, blood samples of the subjects taken up to 12 years previously were then tested for levels of transferrin, the protein that transports iron through the body and brain. The team discovered that subjects with elevated transferrin levels (a sign of an iron-deficient diet) in adolescence had structural changes in brain regions vulnerable to neurodegeneration. The team's analysis of twins revealed a common set of genes that influences both transferrin levels and brain structure. One specific genetic link, a polymorphism involving the HFE gene, associated with reduced brain fiber integrity. Writing that: "Our statistical maps reveal previously unknown influences of the same gene on brain microstructure and transferrin levels,” the study authors submit that: “This discovery may shed light on the neural mechanisms by which iron affects cognition, neurodevelopment, and neurodegeneration.”