According to a new report in the U.S., a sperm donor may have unwittingly passed an extremely rare and dangerous genetic ailment to five children born to four couples.
The case has served to highlight gaps prevalent in the screening process.
The very rare disease, severe congenital neutropenia, can be fatal in children if untreated but it's very rarity means that sperm banks do not screen for it.
Unfortunately the family medical history which sperm donors are requested to provide would not necessarily reveal such a defect, especially if the man is only a carrier and has no symptoms.
Dr. Lawrence Boxer, lead author of the report and director of paediatric hematology and oncology at the University of Michigan is an expert on the disease and says the four couples used the same un-named same sperm bank.
Boxer says the fact is that when couples use a sperm donor they often don't know what they are getting.
Although sperm donors are subjected to mandatory screening for more common genetic disorders such cystic fibrosis and sickle cell anemia, they are not tested for the really rare ones.
The donor's sperm was connected to the children's cases because they all had the same version of the defective gene and because the couples used the same sperm bank.
Boxer says severe congenital neutropenia occurs in about one in five million births and only around 500 children in the United States have the disease.
Apparently children with the condition have a lack of the type of white blood cell that kills bacteria, and develop severe infections shortly after birth.
The American Society of Reproductive Medicine guidelines requests that anonymous sperm donors provide a full family medical history with a history of at least three generations and a complete chromosome screening is not required if a comprehensive family history is taken including potential hereditary disorders.
But the case is not that simple as it is doubtful whether a donor would be aware that a great-grandparent had this particular disease or even if it was recognised three generations back.
It is unclear whether the sperm donor in this case knew he was a carrier but the sperm bank apparently reported that he was in good health.
Boxer says the four children are surviving by having daily injections of a drug that helps build up white blood cells and fight germs, and are well.
However Boxer says they will always have an increased risk of leukemia and a 50% chance of passing the disease to their own children.