A nine-year-old British girl suffering from a rare premature ageing disease will undergo tests in the United States today that could allow her to have life-prolonging treatment.

Hayley Okines ages eight times faster than she should because she suffers from Progeria, a progressive terminal condition which afflicts about 45 people worldwide.

She is expected to have tests today that will mean she will take part in a drug trial at Boston's Children's Hospital. If the tests are successful, the treatment is scheduled for Wednesday.

People born with Progeria look healthy, but begin to display many signs of accelerated ageing at around 18 months old including stunted growth, loss of body fat and aged skin.

Although their mental development is not hampered, children with the condition die of heart disease at an average age of 13, according to the Progeria Research Foundation.

Hayley's mother Kerry, from Bexhill, is hoping the drug trial at Boston's Children's Hospital next week will lead on to the premature ageing process stopping.

Before leaving for the US, she said: "When Hayley was first diagnosed there was no hope. They didn't even know what caused Progeria.

"So, within seven years she has been diagnosed, they have identified the gene that causes it, and now a possible treatment, too.

"At the end of the day we have got nothing to lose, and everything to lose. But the prognosis is not good without it, so we have no choice really."

If tests and assessments prove successful, Hayley will start on medication that has already been given to children with cancer but will be the first clinical trial involving a Progeria sufferer.

Her family first learned of the drug trial at a summit for Progeria sufferers and their families last June.

The new drug has possible side effects including diarrhoea and constipation, forcing Hayley to undergo regular monitoring.

If the treatment goes ahead she will then have to return to Boston every four months to see if the dose can be increased.