A British mother is among nearly 100 women who have had babies by a Danish sperm donor carrying a severe genetic disorder.

Sperm from the unnamed man, identified only as Donor 7042, was used in fertility clinics around the world despite him carrying a defective gene that can cause the disease neurofibromatosis 1 (NF1).

Ten of his offspring have now been diagnosed with the illness, also known as Von Recklinghausen's disease, which causes tumours around nerves, with symptoms including, high blood pressure, bone deformity and learning difficulties, the Mail on Sunday reported.

The Belgian federal health authority has disclosed that a British mother was one of 20 women treated at a Belgian fertility clinic using his sperm.

British women are increasingly turning to Danish donors for so-called ‘Viking babies’, because of a shortage of domestic donors.

Donor 7042 gave sperm at Copenhagen’s Nordic Cryobank, but it was then used in 14 different clinics in America, Canada, Belgium, Island, Georgia, Greece, Spain and Thailand. He is reported to have fathered 99 children.

Denmark was forced to tighten its sperm donation rules after details of the case first emerged in 2012 and it raised questions about country’s flourishing sperm donation industry. Four families are suing the clinic claiming it failed to properly screen the sperm.

The clinic has in the past said that the donor could not be 'clinically classified as having NF1, as it only occurs in some of his cells'. The company says it test for a range of genetic disorders, but 'it is impossible to rule out genetic disease with 100 per cent certainty since it is not possible to test for all inheritable diseases.'

Laura Witjens, from the National Gamete Donation Trust (NGDT), told the paper: “The distribution and use of Danish and American sperm donors is not regulated or monitored, but patients are not told this.

“NF1 is a rare disease, but the terrible spread of the gene via this prolific Danish donor highlights the worrying dangers of the widespread use of a single donor.”

Source: Farmer B. (2015) “British mother in IVF 'Viking ba