Scientists working with embryonic stem cells have made a breakthrough that could revolutionise the understanding of cystic fibrosis, the most common inherited defect in Britain.

Scientists working with embryonic stem cells have made a breakthrough that could revolutionise the understanding of cystic fibrosis, the most common inherited defect in Britain.

The British Association's Science Festival in Exeter was told that researchers had found a way of producing unlimited quantities of human cells carrying the genetic mutation for the disease, which attacks the cells lining the respiratory tract and invariably leads to premature death. Scientists believe that the ability to produce human cells with cystic fibrosis will lead to new drugs and treatments for an incurable disease that affects 7,500 Britons and kills about 150 children and young adults each year.

The research was licensed by the Human Fertilisation and Embryology Authority, which gave permission for the group to study stem cells from spare embryos created by IVF.

Professor Stephen Minger of King's College London told the meeting that his team made the breakthrough by extracting stem cells from a human embryo that carried two copies of the most common cystic fibrosis mutation - one inherited from each parent. "We are licensed to do screening of embryos from families for specific genetic disorders," Professor Minger said.

As part of the pre-implantation genetic diagnosis, a single cell is taken from each three-day-old embryo created by IVF to test for known defects such as cystic fibrosis. "These embryos are segregated into affected and unaffected embryos and only theunaffected embryos are implanted or frozen. All the affected embryos are either donated for research or destroyed," Professor Minger said. "One of the cell lines we've established comes from an embryo that carries the most common mutation for cystic fibrosis."

One in 25 people carries at least one of the mutations for cystic fibrosis. When two carriers have children there is a one in four chance that their child will be affected.

Until now most of the fundamental work on cystic fibrosis has involved studying similar disorders in laboratory animals which have not been perfect models of what happens in humans, Professor Minger said.

"The animal models for cystic fibrosis don't fully recapitulate all aspects of the disease. If you put this particular mutation into an animal it doesn't cause cystic fibrosis," he said.

"As the animal models for cystic fibrosis do not fully repeat all aspects of the disease, having a human cell line with this genetic defect will be very useful. Researchers will be able to use it to study how the mutation affects cells, screen for new treatments, and also look at gene therapy."

Professor Minger's team is now planning to adapt the technique to produce replicating colonies, or lines, of human embryonic stem cells with other inherited disease caused by defects in single genes, such as Huntington's disease. Scientists hope that eventually they could be used to treat a range of incurable illnesses by repairing damaged tissues in situ without recourse to organ transplant.

Britain has led the international effort in this area of medical science since President Bush banned the creation of stem cells derived from human embryos.

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