Dr Eric Kmiec: "This is an exciting and important discovery"

A team from the Jefferson Medical College, Philadelphia, used what they describe as a "gene repair" technique to genetically change white albino mice colour-producing cells to black.

Albino cells lack melanin

Not only did the cells turn black, but the scientists showed for the first time that such changes are both permanent and can be passed to offspring.

They hope the work can be developed into a new form of gene therapy - a type of treatment that can correct the genetic mutations that give rise to some hereditary diseases.

Point mutation

The mutation in albino mice - which gives them their white fur and pink eyes - is caused by a mutation in the tyrosinase gene.

Pigmentation was restored

The mutation inactivates an enzyme that is supposed to make melanin, which gives skin and fur its colour.

By correcting this single alteration in the gene, known as a 'point mutation,' tyrosinase activity was restored and melanin was again produced, changing the colour of the mice cells.

"Melanin-producing cells become normal, changing albino to black," says Dr Kyonggeun Yoon, associate professor of dermatology and cutaneous biology and biochemistry and molecular pharmacology at the Jefferson Medical College, Thomas Jefferson University, Philadelphia.

"Once the mutation is corrected, it takes five or six days for the entire biochemical process to begin producing melanin."

Gene repair

The gene-repair technique was actually developed by Dr Yoon and a colleague, Dr Eric Kmiec, several years ago.

Dr Yoon: A lot of work still needed

It requires the synthesis of a strand of DNA interspersed with its chemical cousin RNA. This small locates and grabs hold of the part of the gene that has the fault and then stimulates the cell's own repair mechanism.

It scans the DNA looking for any mismatches or two strands of DNA that do not seem in sync.

When it finds a mismatch, it replaces one of the chemical bases - the letters in the genetic code - with one that fits better.

Dr Yoon says the gene-repair technique is far from perfected.

"Much more research is needed to improve the design and make this technology generally applicable. Skin is an ideal organ on which to test this technology since it is accessible and can be monitored."

Dr Eric Kmiec comments on the research: "To my knowledge this is the first demonstration of trait reversal in any mammalian system."

The research is published in Nature Biotechnology on 30 November.