Doctors have discovered that a sperm donor in the US has passed on a rare genetic disease to five children born to four couples who used his sperm to conceive. The disease, severe congenital neutropenia (SCN), can be fatal in children if untreated but is so rare that sperm banks do not typically test for it. Even though donors are asked to give full details about their medical and family history, the information they provide would not necessarily ever indicate the presence of the risk, especially if the man had no symptoms of the condition himself or was only a carrier.
Although the provision of fertility treatment is not regulated in the US, guidelines issued by the American Society of Reproductive Medicine (ASRM) state that anonymous gamete donors must provide a family medical history that goes back for at least three generations. The ASRM guidelines also state that full chromosomal screening is not needed where there is a proper family history detailing any potential heritable disorders. Sperm donors are routinely screened for more common genetic disorders, such as cystic fibrosis or sickle cell anaemia, but not for more rare genetic diseases.
The cluster of SCN cases was identified by the SCN International Registry and by Dr Laurence Boxer, director of paediatric haematology and oncology at the University of Michigan and an expert on the disease. Although the researchers did not have sperm samples to test, as the clinic had discarded the remainder of the man's sperm, they concluded that the children affected could all be traced back to the sperm of one man because the four couples with affected children all used sperm from the same sperm bank in Michigan, US, and all had the same version of the defective gene. Dr Boxer, who co-authored a report on the findings published in the Journal of Paediatrics, refused to identify the sperm bank by name, or say where the couples treated came from, and stated that it was not known whether the man concerned knew he was a carrier - the sperm bank only reported that the man concerned was 'healthy'. Dr Boxer speculates that as the man was otherwise healthy, he must have had an unusual condition called mosaicism, in which the mutated gene was carried only in his sperm and not in the rest of his body. 'Otherwise he would have been a very sick man', he said.
SCN occurs in only about one in 5 million births - children born with the disease cannot make the type of white blood cell that kills bacteria in the body and, as a result, they are unable to fight infections. The children affected are receiving treatment which helps them to build up their white blood cell production, said Dr Boxer. But he added that they will always have a greater risk of developing leukaemia than other children and all face a 50 per cent chance of passing the condition on to their own children. 'The bottom line is, when you use a sperm donor, you really don't know what you're getting', he said, adding that prospective parents should be advised that screening of donors will not always identify all potential genetic diseases. 'The mothers need to be prepared that there is always an inherent risk of a genetic disorder being transmitted by the donor's sperm', he advised.