The marriage of British twins separated at birth has startled the UK and raised fears of unwitting incest due to anonymous egg and sperm donors. The case was disclosed by Lord Alton during a debate in the House of Lords on new fertility legislation. Their marriage was quietly annulled last year, with a judge ruling that it had never existed. They had met as adults and felt "an irresistible attraction". Lord Alton used the case to argue that that birth certificates should be changed to include information on both genetic parents, as well as whether or not the child was conceived by a sperm donor. He described anything less as a violation of human rights: "The state is colluding in a deception. We are opening the door to more cases like this one."

The tragic case highlighted the growing possibility of unwitting incest in the population, now that as many as one child in 25 is born through IVF in some countries. Back in 2002, an Australian researcher called for free DNA testing to avoid the dangers of inbreeding. Dr Panos Ioannou wrote in the journal Nature that "In most cultures, at least a small percentage of children are born through infidelity. Added to that, as many as 10% of couples now use assisted reproduction, often involving the use of gametes from unknown donors. Children born through such practices are likely to be of similar ages and to grow up in the same area. A significant percentage of couples may, unknowingly, be closely related."

The problem could be particularly acute in the US where there is  almost no regulation of IVF, even though the technology is responsible for about 1% of all births. "As half-siblings find one another, it is becoming clear that the banks do not know how many children are born to each donor, and where they are. Popular donors may have several dozen children and critics say there is a risk of unwitting incest between half-siblings," the New York Times has reported.

And the soap opera scenario of "irresistible attraction" may have a scientific basis, although there is only anecdotal evidence for it at the moment. Post-adoption agencies say that nearly half of reunions between siblings or parents and offspring result in obsessive attachments and emotions which sometimes lead to incest. "Genetic sexual attraction associated with IVF births is a time bomb waiting to go off," Sue Cowling, the deputy director of the Post-Adoption Centre in the UK, warned a few years ago

Related stories:
Guardian, May 17, 2003;
 New York Times, Nov 20, 2005;
Nature, Sept 19, 2002;
London Times, Jan 13, 2008