Heavy metals, such as iron and manganese, are involved in neurologic disease. Most often these diseases are associated with abnormal environmental exposures or abnormal accumulations of heavy metals in the body. There is increasing recognition that heavy metals normally present in the body also may play a role in disease pathogenesis through free radical formation. When a part of the brain known as the basal ganglia is affected, movements become disordered.

 Parkinson's disease is one of the most common movement disorders and is related to destruction of neurons in the substantia nigra pars compacta (SNpc) of the basal ganglia. The combination of high concentration of iron and the neurotransmitter, dopamine, may contribute to the selective vulnerability of the SNpc. Dopamine can auto-oxidize to produce free radicals particularly in the presence of iron and other heavy metals.