New Zealand and Australian scientists have observed DNA moving between animal cells in a breakthrough discovery that could lead to better understanding of a range of human diseases and new gene therapies.

The team led by Professor Mike Berridge, of the independent Wellington-based Malaghan Institute, claimed to be the first in the world to demonstrate mitochondrial DNA movement between cells in an animal tumor.

The research laid important groundwork for understanding human diseases other than cancer, since defective mitochondrial DNA was known to account for around 200 diseases and was implicated in many more, Berridge said in a statement Wednesday.

It could also usher in a new field where synthetic mitochondrial DNA is custom-designed to replace defective genes.

In mouse models of breast cancer and melanoma that had had their mitochondrial DNA removed, replacement DNA was acquired from surrounding normal mouse tissue. After adopting this new DNA, the cancer cells went on to form tumors that spread to other parts of the body.

"Our findings overturn the dogma that genes of higher organisms are usually constrained within cells except during reproduction. It may be that mitochondrial gene transfer between different cells is actually quite a common biological occurrence," said Berridge.

Tests showed the mitochondrial DNA had been obtained from non- tumor cells and the next challenge was to find out how this was possible.

"Whether this new phenomenon is important in tumour formation is still unclear, but we are interested in pursuing the research to see if the transfer occurs more widely in the body. Preliminary evidence indicates it may be a common occurrence in the brain," said Berridge.

Many copies of mitochondrial DNA, a small circular bacterial- like genome, were found inside each mitochondria, an organelle found in most animal cells that helps the cell process energy.

Mitochondrial DNA was unrelated to nuclear DNA, which encodes a person's primary genetic instructions, including characteristics such as hair colour, height and sex.

Mitochondrial DNA was inherited solely from a person's mother -- a trait that had been used to trace all living humans back to a common ancestor who lived in Africa 60,000 to 70,000 years ago.