Oliver Conway

But a Europe-wide investigation has found that one sperm donor, who fathered nearly 200 children, unwittingly passed on a genetic mutation that dramatically increased their risk of cancer.

Celine, not her real name, is a single mother in France whose child was conceived 14 years ago.

She received a call from her fertility clinic in Belgium urging her to get her daughter screened.

She told us of her fears over the possibility her child may develop cancer.

We have translated her words.

Some of the children have already died, and only a minority who inherited the mutation will manage to avoid the disease entirely.

I heard more from our health correspondent, James Gallagher.

So this sperm donor donated back as a student in 2005, and we think that that sperm was used in around 67 fertility clinics across 14 countries.

And the European Sperm Bank said it would have not been possible to detect the mutation this man had by preventatively genetically screening him.

And once they did know that he carried this mutation, it was immediately blocked.

But so many women and families are affected and the sperm was used by so many people.

It's because fertility rules don't work across country borders.

So if you were to go to Belgium or Germany or Greece, each of those countries would have a limit on how often a sperm donor can be used in how many different families in that country.

But there's nothing that stops you selling sperm to each and every one of those countries.

And that's what's happened.

The European Sperm Bank in Denmark said,

has collected this man's sperm and sold it into multiple countries, and that's why we have this figure of at least 197 children being born.

And it could be more than that, because we haven't got data back through this investigation from all the countries where we know the sperm was sold.

There have been calls, though, for limits to be put in.

It's worth stressing, though, that...