Oliver Conway

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,

The amount of testing that you have is like you have your brain scanned every year.

You have the rest of your body scanned every year.

You need ultrasounds of your stomach because these cancers can appear in multiple different organs within the body.

It is a life changing diagnosis for these families.

The donor isn't affected.

He acquired mutations and that has affected his sperm.

So most of his body does not contain this defective form of the TP53 gene, but around 20% of his sperm do carry the risk.

And it's really worth stressing in this that the donor was unaware.

As far as we understand, he was donating completely in good faith and didn't find out that he was carrying this mutation in his sperm until quite recently.