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Hello and welcome to News Out from the BBC World Service.
We're coming to you live from London.
I'm Sean Lay.
Around 200 children across Europe born from sperm donated by the same donor face an elevated risk of cancer.
Some have already died.
The donor who began giving sperm as a student in 2005 was unaware at the time of a genetic mutation found in one-fifth of his sperm.
Those born from the affected sperm face a 90% risk of developing cancer before their 60.
The sperm was sold by Denmark's European Sperm Bank and used by 67 fertility clinics across 14 countries.
Celine, which is not her real name,
is a single mother in France whose child was conceived 14 years ago.
She received a call from the fertility clinics used in Belgium,
urging her to get her daughter screened.
Her words are voiced by one of our production team.
We don't know when.
We don't know which one.
And we don't know how many.
I understand that there's a high chance it's going to happen, and when it does, we'll fight.
And if there are several, we'll fight several times.