A sperm donor who unknowingly harbored a genetic mutation that dramatically raises the risk of cancer has fathered at least 197 children across Europe, a major investigation has revealed.
Some children have already died and only a minority who inherit the mutation will escape cancer in their lifetimes.
The sperm was not sold to UK clinics, but the BBC can confirm a very small number of British families, who have been informed, used the donor's sperm while having fertility treatment in Denmark.
Denmark's European Sperm Bank, which sold the sperm, said families affected had their deepest sympathy and admitted the sperm was used to make too many babies in some countries.
The investigation has been conducted by 14 public service broadcasters, including the BBC, as part of the European Broadcasting Union's Investigative Journalism Network.
The sperm came from an anonymous man who was paid to donate as a student, starting in 2005. His sperm was then used by women for around 17 years.
He is healthy and passed the donor screening checks. However, the DNA in some of his cells mutated before he was born, damaging the TP53 gene, which has the crucial role of preventing the body's cells turning cancerous.
Doctors linked to the case report that some children have developed multiple cancers, with some having unfortunately passed away at a young age. MRI scans and ultrasounds are now routine for monitoring these children.
Families are now urged to consult their clinics for screening and information, as the implications of such genetic variations can dramatically alter the health trajectories of those affected.
