A sperm donor who unknowingly harboured a genetic mutation that dramatically raises the risk of cancer has fathered at least 197 children across Europe, a major investigation has revealed, BBC reported. 

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, according to BBC.