Washington, May 22 (IANS) The exact causes of neuro-degenerative disorders like Alzheimer's and Parkinson's disease are unknown, but scientists say excess of copper and iron in the human brain may be one of the influencing factors.

Another is DNA damage by reactive oxygen species, highly destructive molecules usually formed as a byproduct of cellular respiration.

Researchers from the University of Texas Medical Branch at Galveston have discovered how these two pieces of the neuro-degenerative disease puzzle fit together, the Journal of Alzheimer's Disease reports.

"Reactive oxygen species cause the majority of the brain cell DNA damage that we see in Alzheimer's and Parkinson's disease, as well as most other neuro-degenerative disorders," said post-doctoral fellow Muralidhar Hegde, who led the study.

Alzheimer's sufferers may repeat statements and questions over and over, forget chats, appointments or events, routinely misplace possessions, often putting them in illogical locations. Eventually they forget the names of family members and everyday objects.

Humans ordinarily have small amounts of iron and copper in their bodies - in fact, the elements are essential to health, according to a Texas statement.

But some people's tissues contain much larger quantities of iron or copper, which overwhelm the proteins that normally bind the metals and sequester them for safe storage.

The result -- so-called 'free' iron or copper ions circulating in the blood are able to initiate chemical reactions that produce reactive oxygen species.

A high level of copper or iron, they say, can function as a "double whammy" in the brain by both helping generate a large numbers of the DNA-attacking reactive oxygen species and interfering with the machinery of DNA repair that prevents the deleterious consequences of genome damage.