A sperm donor who unknowingly harboured a cancer-causing genetic mutation has fathered at least 197 children across Europe — some of whom have already died.
Only a minority of children who inherit the mutation will escape cancer in their lifetimes, it is understood.
While the sperm was not sold to clinics in the UK, a “small number” of British families have been affected after they received fertility treatment in Denmark.
Denmark’s European Sperm Bank, which sold the sperm, expressed its “deepest sympathies” for the families affected, admitting the sperm had been used to make too many babies.
Fourteen public service broadcasters, including the BBC, were involved in the investigation.
Back in 2005, an anonymous man was paid to donate his sperm, which was later used by women trying to conceive for around 17 years.
The man was healthy and passed the relevant donor screening checks; however, some of his cells mutated before he was born.
The TP53 gene — which plays a crucial role in preventing the body’s cells from turning cancerous — was damaged.
Most of the donor’s body does not contain the dangerous form of TP53, but 20% of his sperm do.
As a result, the man has passed down this genetic mutation to the children conceived from his sperm, which will be in every cell of their bodies.
Professor Clare Turnbell described the revelation as a “dreadful diagnosis”, adding “it’s a very challenging diagnosis to land on a family”.
She told the BBC: “There is a lifelong burden of living with that risk, it’s clearly devastating.”
MRI scans of the body and the brain will be needed every year, as well as abdominal ultrasounds, to try and spot any tumours.
The European Sperm Bank said the "donor himself and his family members are not ill" and such a mutation is "not detected preventatively by genetic screening".
They said they "immediately blocked" the donor once the problem with his sperm was discovered.
