Oliver Conway

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...

Even if you reduced the number of times a sperm donor sperm was used, it doesn't necessarily reduce the risk of inheriting rare genetic diseases.

But a lot of it is around psychological harm, actually, because there's a lot of discussion about what it means to be one of these children.

If you suddenly find out you have hundreds of half siblings.

And how common is this genetic mutation and what damage does it do?

Right, this genetic mutation is normally incredibly rare.

It's something called TP53, and its role in the body is to help prevent cancer.

And if it's defective, it causes a rare syndrome, and that increases your risk of cancer in your lifetime to up to 90%.

So it really dramatically raises your risk of cancer.

I mean, this is absolutely a horrific diagnosis.

I mean, just imagine that you had your child and then you get a phone call from a fertility clinic that you haven't been back to for years telling you that you need to get your child tested for this rare genetic disorder.

And if you find out that they're pretty certain going to get cancer at some point in their lifetime and up to 90% risk,