I posted yesterday on a serious incident at 23andMe’s sample processing lab, LabCorp, that resulted in the wrong data being sent to up to 96 customers. The company has just posted a blog entry explaining the cause of the problem and the approaches being taken to ensure it doesn’t happen again.
As several commenters had speculated, the cause of the problem appears to have been the flipping of a 96-well plate (a solid block of plastic containing 96 separate samples in individual wells) by 180 degrees, resulting in all of the samples being in the incorrect locations for downstream analysis.
I’m frankly astonished that this was possible at an accredited genotyping facility – plate-flipping is an age-old problem, but trivial to prevent with good plate/machine design that only allows plates to be loaded in a single orientation. And indeed, in the post 23andMe announces that LabCorp “has adjusted the mounting process for these 96-well plates and this new adjustment physically prevents any incorrect manual placement of the plates used at this step of processing”. It boggles the mind that LabCorp didn’t see fit to do this earlier.
In the comments thread on my post yesterday there was discussion about additional steps that could be taken by 23andMe to spot such mix-ups in future. Neil Walker noted that matching subject sex with that inferred from genotype data is a routine component of quality control in large-scale academic genomic studies, and I suggested a slightly expanded approach:
There’s no reason not to have an “opt-in” questionnaire when people register on the website (after mailing off their sample) for the purposes of sample tracking: sex, eye colour and hair colour alone would be a start. If even 50% of customers filled in these details that would be enough to spot a dodgy plate with high confidence, even allowing wiggle room for incorrect answers given by some customers.
It looks as though the company will be adopting at least a basic version of this approach: the 23andMe post says that “23andMe will collect data regarding sex for all new customers prior to laboratory processing so an additional quality check can be conducted prior to uploading data”.
More elaborate plate-tracking measures – such as the incorporation of known control samples at different positions in each plate being processed, serving as a kind of molecular barcode – are not discussed, but these might be a worthwhile investment if the company is to avoid a repeat of the horrendous negative publicity aroused by this incident.
The bulk of the blame for this incident must be laid squarely on LabCorp, who failed to adequately protect against an extremely well-known source of sample mix-ups. However, it’s worth noting that 23andMe routinely suggests that customers fill in basic surveys (which – from memory – include sex and other useful physical traits) after mailing in their kit but before their results are returned. If even a fraction of customers had filled in these surveys with some degree of accuracy – which I suspect they had – and if 23andMe had used this information to compare against the results from each plate, this mix-up would almost certainly have been spotted well before any customer received potentially distressing and erroneous results.
Still, kudos to 23andMe for responding to this problem, rapidly implementing a solution, and discussing the situation openly – and for other personal genomics companies out there, hopefully this has been an important lesson in the negative PR impact of quality control problems.