A sperm donor unknowingly carrying a dangerous genetic mutation linked to cancer has fathered at least 197 children in Europe. The donor's mutated TP53 gene, causing Li Fraumeni syndrome, greatly increases cancer risk, sometimes up to 90% in a lifetime. The sperm was donated starting in 2005 by an anonymous healthy man. About 20% of his sperm carried the mutation. Children conceived with affected sperm inherit the mutation in all their cells, facing high cancer risks including childhood cancers and breast cancer. The European Sperm Bank, based in Denmark, sold this sperm to 67 clinics in 14 countries. They have apologized, saying families have their "deepest sympathy" and admitted the sperm was used to produce too many babies in some places. Although the sperm was not sold to UK clinics, a "very small" number of British women traveled to Denmark and used the donor's sperm. They have been told of the risks by the clinics. Doctors found 23 children with the mutation among 67 tested and 10 have already had cancer. Some children have died young. Dr Edwige Kasper from Rouen University Hospital said, "We have some children that have developed already two different cancers and some of them have already died at a very early age." One mother from France, who asked to remain anonymous, said she has "absolutely no hard feelings" but called it unacceptable that unsafe sperm was used. She worries about cancer looming over her daughter’s future. There is no international law limiting how many children a sperm donor can father. The European Sperm Bank broke limits in some countries, selling sperm that fathered 53 children in Belgium where the limit is six families. The UK limit is 10 families. Experts say total safety is impossible. Prof Allan Pacey said, "You can't screen for everything." Still, calls for stricter limits and better screening grow louder to protect children. The European Society of Human Reproduction and Embryology suggests a 50-family limit but notes this won't reduce rare genetic disease risks. Concern also grows for social and psychological effects of having hundreds of half-siblings. The European Sperm Bank stressed that donor sperm is often the only way for many to have children and it remains safer than most natural options when proper screening happens. Parents using donor sperm are advised to check the donor's background and use licensed clinics. Support is available for affected families through organizations like BBC Action Line.