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Wednesday, 27 September, 2000, 05:13 GMT 06:13 UK
Scientists introduce mito-mouse
Mito-mouse University of Tsukuba
Mice with mitochondrial diseases will aid research into human disorders
Japanese researchers have succeeded in making a mouse that mimics the problems experienced by people who suffer rare but debilitating disorders related to the body's inability to process energy properly.

So-called mitochondrial diseases are thought to affect as many as one in 10,000 children in the UK.

Individuals display a vast array of symptoms from poor growth and heart disease to diabetes and neurological problems.

Scientists say mito-mouse, as it has been dubbed, will help them study the diseases in more detail and help them find new and more effective treatments.

Impossible task

Mitochondria are tiny structures that reside outside the nucleus of a cell and play a crucial role in the conversion of food into energy.

Unusually, they posses their own DNA molecules (mtDNA). Defects, or mutations, in the genes carried on this DNA can result in a wide variety of disorders that can appear at any time from the foetal stage and early infancy to late adulthood.

Scientists would normally attempt to make a mouse that displayed similar genetic defects to aid their research into the mechanisms involved in the diseases.

But the creation of a mitochondrial mouse was thought to be impossible due to the difficulties in introducing and maintaining DNA in mitochondria.

Cell culture

However, Dr Jun-Ichi Hayashi and colleagues, of Tsukuba University in Japan, announced on Tuesday that they had succeeded in making the first animal model of mitochondrial disease.

The researchers collected the mutant mitochondria that naturally develop in the nerve endings in the brains of ageing mice.

These were put in a special cell culture and screened to identify the most appropriate defects before being fused into embryos that were implanted into surrogate mothers.

The mouse model the Japanese scientists produced has interesting similarities and differences with people suffering from mitochondrial disorders.

Unexpected diseases

In particular, many of the mito-mice created at Tsukuba died of kidney failure which is not normally associated with the human disorders.

Dr Jun-Ichi Hayashi told BBC News Online that this may be because some conditions have yet to be correctly ascribed to mitochondrial defects.

"We believe that the kinds of diseases caused by mtDNA mutations will be more widespread than previously thought, and we hope to show that unexpected diseases are caused by mtDNA mutations as in the renal failure."

Dr Eric Shoubridge, of the Montreal Neurological Institute, Canada, described the Japanese work as a technical tour de force.

"This allows us to get at some of the basic biology of mitochondrial genetics that we can't do in humans because we don't have access to the tissues except those we can obtain by biopsies," he said.

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