British and American scientists have identified a gene responsible for babies being born with a form of cleft lip and palate, a disfigurement which even the best modern surgery cannot always completely correct.
In the long term, the discovery could lead to treatments for cleft lip and palate while a baby is still in the womb.
In the short term, a difficult ethical decision may have to be made by the human fertilisation and embryology authority (HFEA) over whether the condition is serious enough to allow the screening of embryos with the possible destruction of those that carry the gene.
The gene causes a rare form of cleft lip and palate called Van der Woude syndrome, which affects about 2,000 of the approximately 100,000 people in the UK who were born with the condition.
Modern surgical techniques - which grew out of expertise gained in the Battle of Britain - mean that many born with the more common forms of cleft lip and palate grow up with only minimal scarring as a consequence.
Others, and most of those with Van der Woude syn drome, suffer more serious effects. Besides cleft lip and palate, Van der Woude babies tend to grow up with pits in their lips and missing teeth.
Most forms of cleft lip and palate are thought to be caused by as yet unknown environmental and genetic factors acting on babies in the womb. But Van der Woude was known to be inherited, in a pattern than suggested a single mutated gene.
Today, scientists from Manchester University and the University of Iowa announce in the online version of the journal Nature Genetics that they have identified the gene, IRF6.
The researchers, later aided by scientists at the Sanger centre in Cambridge, have been hunting the gene for more than a decade, and had narrowed it down to a single chromosome.
Their breakthrough came last year with the examination of twins in Brazil who were genetically identical in virtually every respect, except that one had Van der Woude and the other did not. By comparing their copies of chromosome 1, it was easy to spot the genetic difference - a single deviation from the norm among 3bn letters of genetic code.
"Every 11 minutes a child is born somewhere in the world with a cleft lip and palate," said Michael Dixon, who led the UK end of the research. "This gene is certainly one of the most important to be identified.
"It will be at least 10 years before any treatments are available, but in the short term, families affected by Van der Woude will have a genetic test available that will help them prepare in advance for having a child with this syndrome."
Scientists hope the research, funded by the Wellcome Trust and Action Research, will eventually lead them to the environmental cause of more common forms of cleft lip and palate. Expectant mothers could then be given lifestyle advice or dietary supplements to counter the cause.
More controversially, people carrying the Van der Woude gene could seek IVF treatment and have the embryos screened for the gene before implantation in the mother's womb. Only non-carrier embryos would be implanted; the rest would be destroyed.
A Van der Woude carrier has a 50% chance of passing the gene on to any offspring.
The screening technique, known as PGD, needs to be ap proved by the HFEA for each new gene. "This is difficult, because of the nature of the condition," said Professor Dixon. "We're not talking about something that's going to cause death at a very early age, so the regulatory bodies would have to take that into account."
