Flynn and her husband wanted to have more children, partly because a bone-marrow transplant from a healthy sibling would be Jordan's best shot at survival. They decided to undergo pre-implantation genetic diagnosis, an IVF technique designed to ensure only healthy embryos are implanted. A Detroit-based lab, Genesis Genetics Institute, isolated two apparently disease-free embryos that would be bone-marrow matches for Jordan and implanted them at a hospital in Atlanta in early 2003. Julia and Jorjia were born 34 weeks later. Both have Fanconi anaemia.

Fortunately, reports of such errors connected to clinical genetic testing are extremely rare. Mark Hughes, the founder and chief clinician at Genesis, says that since the earliest days of his company 17 years ago, there have been only nine such instances out of several thousand tests conducted. "There is going to be an error rate in any diagnostics, and it's especially tricky in this instance," he says, because genetic testing relies upon identifying a very short DNA sequence among the large volume of DNA that comprises the human genome.

Human error may also play a part. In the Flynns' case, a genetic test on Julia's bone marrow suggests a match with one of the eggs diagnosed as diseased, which may have resulted from a simple mix-up of samples, although no firm conclusion has been reached. But no one can say which samples got mixed up and when and where the error could have occurred. Flynn did not follow up the implantation with the recommended amniocentesis that could have detected the disease before birth.

However, last week another case highlighted the potential costs of a lab or hospital getting a genetic test wrong.
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15-Mar-2006