Embryo screening for common diseases: coming soon?

A Nature News article describes the growing availability of technology that allows the screening of human embryos for hundreds of different genetic disorders prior to implantation.

The technology is based on the same type of chips used by personal genomics companies like 23andMe, but the chips used for embryo screening would initially be used to target known rare disease-causing mutations or large chromosomal abnormalities rather than performing a genome-wide scan for common variants (in the article, a screening company director describes the targeted diseases as "nasty, early-onset and ethically uncomplicated"). Such testing is generally accepted by Western society, as witnessed by the extremely high rate of termination of trisomy 21 embryos.

However, the article also notes that there's currently nothing to stop companies from including variants on the chips that provide information about adult-onset diseases like diabetes or Alzheimers - indeed, in the UK there have already been embryos screened for breast cancer risk variants. This type of screening currently raises some serious ethical eyebrows, but perhaps not for long: the article argues that "as the technology advances, consumer demand is likely to overwhelm societal ethical qualms" - and I'd tend to agree, in general.

However, before we get too carried away by visions of a Gattaca-style future, it's worth noting a couple of serious obstacles in the path of widespread adoption of the use of this technology to screen for common disease genes.

There are two major hurdles: firstly, current methods require that parents undergo IVF (a procedure that only accounts for around 1% of live births even in most industrialised countries); and secondly, the probabilistic complexities of screening for genes underlying common diseases are seriously daunting. With hundreds of different common variants (and untold numbers of rare variants) underlying common diseases, no embryo will be completely free of genetic risk factors - instead, prospective parents would face a decision between embryos that all carry increased risk of at least some common diseases.

So I've no doubt we'll soon see widespread screening for simple, severe diseases among couples already undergoing IVF, but the general unpleasantness and uncertainties of current IVF technology will probably hold most couples back from adopting embryo screening as a matter of course; and even if IVF technology improves to the point that it becomes something that people choose over natural conception (a highly dubious scenario, at least for the immediate future), the probabilistic challenge will still make screening for common diseases a tough and complex choice for parents-to-be.

There are alternatives to IVF: non-invasive genetic tests that involve isolating fetal DNA from a pregnant woman's blood are already offered commercially for RhD incompatibility by Sequenom, who also currently have a trisomy 21 test in clinical trials and today announced plans to extend testing to a wide range of genetic disorders. However, such tests analyse only a single implanted embryo rather than the multiple embryos tested prior to IVF, and parents face the trauma of terminating an existing pregnancy (rather than simply choosing not to implant an embryo) if the news is bad. Such tests will no doubt ultimately become as routine as ultrasounds for expectant parents, and will be valuable for early detection of severe early-onset disorders - but it's highly unlikely that pregnancies will ever be routinely terminated for embryos who carry, say, a 27% higher risk of developing obesity.

It's also important to take a long-term view here: barring apocalyptic catastrophes, the current rate of progress in medicine means that most common adult-onset disorders will likely be highly treatable by the time our children reach the age of onset. Even a substantially elevated risk of type 2 diabetes doesn't seem quite so alarming when you consider that the disease likely won't even exist as a major health concern in industrialised countries by the time your child is old enough to be buying her own Twinkies.

Of course, that does assume that the health system of your particular industrialised country will continue to ensure that the relevant treatment is affordable...

Subscribe to Genetic Future via RSS.