A sperm donor who unknowingly carried a genetic mutation that significantly increases the risk of cancer fathered at least 197 children across Europe, according to a major investigation.

Some children have already died and only a minority who inherit the mutation will escape cancer during their lifetime.

The sperm was not sold to UK clinics, but the BBC can confirm that a "very small" number of British families, who have been informed, used donor sperm during fertility treatment in Denmark.

The European Sperm Bank in Denmark, which sold the sperm, said it had "its deepest condolences" to the affected families and acknowledged that the sperm was used to make many babies in several countries.

The investigation was carried out by 14 public broadcasters, including the BBC, as part of the European Broadcasting Union's Investigative Journalism Network.

The sperm came from an anonymous man who was paid to donate as a student, starting in 2005. His sperm was then used by the women for about 17 years.

He is healthy and passed the donor screening tests. However, the DNA in some of his cells mutated before he was born.

It damaged the TP53 gene - which plays a crucial role in preventing the body's cells from turning cancerous.

Most of the donor's body does not contain the dangerous form of TP53, but up to 20% of his sperm does.

However, any child born from affected sperm will have the mutation in every cell of their body.

This is known as Li Fraumeni syndrome and comes with a chance of up to 90% of developing cancer, especially during childhood, as well as breast cancer later in life.

"It's a terrible diagnosis," Professor Clare Turnbull, a cancer geneticist at the Institute of Cancer Research in London, told the BBC.

"It's a very challenging diagnosis to place on a family, there's a lifelong burden of living with that risk, it's clearly devastating," she added.

MRI scans of the body and brain are needed every year, as well as abdominal ultrasounds, to try to detect tumors. Women often choose to have their breasts removed to reduce their risk of cancer.

The European Sperm Bank said that "the donor himself and his family members are not sick" and such a mutation "is not detected preventively by genetic screening."

They said they "immediately blocked" the donor once the problem with his sperm was discovered.

Doctors who were seeing children with cancer linked to sperm donation raised concerns at the European Society of Human Genetics this year.

They reported finding 23 with the variant out of 67 children known at the time. Ten had already been diagnosed with cancer.

Through Freedom of Information requests and interviews with doctors and patients, we can discover that many more children have been born to the donor.

The figure is at least 197 children, but this may not be the final number as data was not obtained from all countries.

It is also not known how many of these children have inherited the dangerous variant.

Dr. Edwige Kasper, a cancer geneticist at the University Hospital of Rouen, in France, who presented the initial data, told the inquiry: "We have many children who have already developed one cancer. We have some children who have already developed two different cancers and some of them have already died at a very young age."

Céline, not her real name, is a single mother in France whose child was conceived with donor sperm 14 years ago and has the mutation.

She received a call from the fertility clinic she used in Belgium, urging her to have her daughter checked.

She says she has "absolutely no ill feelings" towards the donor, but says it was unacceptable that she was given sperm that "wasn't clean, that wasn't safe, that carried a risk."

And she knows that cancer will threaten them for the rest of their lives.

"We don't know when, we don't know which one, and we don't know how many," she says.

"I understand that there is a high chance that it will happen and when it does, we will fight and if... There are some, we will fight several times," she added.

Donor sperm was used by 67 fertility clinics in 14 countries. The sperm was not sold to UK clinics.

However, as a result of this investigation, authorities in Denmark notified the UK's Human Fertilisation and Embryology Authority (HFEA) on Monday that British women had travelled to the country to receive fertility treatment using donor sperm. These women have been informed.

Peter Thompson, the HFEA's chief executive, said a "very small number" of women had been affected, and "the Danish clinic where they were treated told them about the donor".

It is not known whether any British women have received treatment in other countries where donor sperm has been distributed.

Concerned parents are advised to contact the clinic they used and the fertility authority in that country.

The BBC is choosing not to publish the donor's identification number because he donated in good faith and known cases in the UK have been contacted.

There is no law on how many times a donor's sperm can be used worldwide. However, individual countries set their own limits. The European Sperm Bank admitted that these limits had "unfortunately" been breached in some countries and was "in dialogue with the authorities in Denmark and Belgium".

In Belgium, a single sperm donor is supposed to be used by only six families. Instead, 38 different women produced 53 children for the donor.

The limit in the UK is 10 families per donor.

Professor Allan Pacey, who once ran the Sheffield Sperm Bank and is now vice-chancellor of the Faculty of Biology, Medicine and Health at the University of Manchester, said countries had become dependent on large international sperm banks and half of the UK's sperm was now imported.

He told the BBC: "We have to import from the big international sperm banks who are selling it to other countries too, because that's how they make their money, and that's where the problem starts, because there is no international law on how often sperm can be used."

He said the case was "terrible" for everyone involved, but it would be impossible to make sperm completely safe.

"You can't screen for everything, we only accept 1% ​​or 2% of all men who apply to become sperm donors in the current screening agreement, so if we make it even stricter, we won't have any sperm donors - that's where the balance lies," he added.

This case, along with that of a man who was ordered to stop after fathering 550 children through sperm donation, has again raised questions about whether there should be stricter restrictions.

The European Society of Human Reproduction and Embryology recently suggested a limit of 50 families per donor.

However, she said this would not reduce the risk of inheriting rare genetic diseases.

On the contrary, it would be better for the well-being of the children who discover that they are one of hundreds of half-siblings.

"More needs to be done to reduce the number of families born globally from the same donors," said Sarah Norcross, director of the Progress Educational Trust, an independent charity for people affected by infertility and genetic conditions.

"We don't fully understand what the social and psychological implications of having these hundreds of half-siblings will be. It could be potentially traumatic," she told BBC News.

The European Sperm Bank said: "It is important, especially in light of this case, to remember that thousands of women and couples do not have the opportunity to have a child without the help of donor sperm.

"It is generally safer to have a child with the help of donor sperm if sperm donors are screened according to medical guidelines," they added.

Sarah Norcross said these cases were "simply rare" when considering the number of children born to a sperm donor.

All the experts we spoke to said that using a licensed clinic meant that sperm would be screened for more diseases than most prospective fathers.

Professor Pacey said he would ask "is this a UK donor or is this a donor from some other country?"

"If it's a donor from another country, I think it's legitimate to ask questions about whether that donor has been used before? Or how many times this donor will be used," he added. /Telegraph/

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