The donor, known only as 'donor 7042', is believed to have fathered 43 children in ten countries, and had his sperm distributed to 14 clinics. Of the 43 children conceived using the donor's sperm, at least five have inherited the nerve disorder Neurofibromatosis type 1 (NF1) also known as Von Recklinghausen's disease.
NF1 is caused by a genetic mutation that shows autosomal dominant inheritance, such that children of a parent carrying this mutation have a fifty percent chance of inheriting the disorder. However in some cases of the disease, the mutation is not inherited from the parents and arises spontaneously. NF1 is a condition that is characterised by benign tumours, bone deformity, high blood pressure and learning difficulties. There is no cure but symptoms may be managed.
'In the case of these five, we know the disorder came from the donor even though the disorder is not always transmitted by a person's parents', said Mr Peter Bower, director general of the clinic Nordisk Cryobank in Copenhagen, where donor 7042 made his sperm donation.
Although the clinic was first told in June 2009 that one of the donor's children had been diagnosed with NF1, the donor's sperm was subsequently used in further inseminations. 'Our team of physicians and our geneticist looked at the case but didn't consider there to be reason enough to suspect it was the donor and therefore no reason to stop the use of his sperm', said Mr Bower to the Swedish news outlet, The Local.
The clinic's website states that all sperm is screened for cystic fibrosis and HIV, human immunodeficiency virus but does not say whether the screening also includes NF1.
Denmark will introducing new rules as a response to this case. Each donor will be allowed to have his sperm used in a maximum of 12 inseminations from 1 October. Although donor 7042 fathered 43 children, the limit at the time was 25 and it is unknown how the donor was able to exceed this.
Nordisk Cryobank currently pays 300 Kroner (£32) per successful sperm donation. Ms Sonja Pedersen, the mother of an affected child, told the BBC: 'We are dealing with a lot of children, but there is also the economical aspect. They earn a lot of money doing this. And one has a responsibility to make sure that the product, so to speak, is all right'.