Another controversial theory is the manganese overload-copper deficiency proposal. Prions should bind copper but may bind manganese if copper is deficient and manganese is excessive. The theory resulted from circumstantial evidence gained from the fact that in the United Kingdom farmers were treating cows with an insecticide that depleted copper and feeding them with a supplement high in manganese. Noted too was the fact that in earlier times manganese miners used to suffer from a disease that was similar to Creutzfeldet-Jakob disease (CJD). Other elements such as iron, selenium, and zinc have also been implicated.
Yet another theory proposes that the protein-based infectious prions convert normal proteins into prions by conversion rather than by replication.