It has been a minute since I last posted, please accept my apologies and thank you for sending messages asking for more. Your support is much appreciated. 🙂
Interestingly enough, this is the second time I have had to put things on hold due to a number of unforeseen circumstances and again the first thing I see being blasted all over standard newspapers and science blogs is a genetics story. Yaaaay. But only because it is so much easier for me to talk about my own specialty than anything else. I’m not biased at all LOL.
At the beginning of this month, Kitzman, J. O. et al. (2012) published work in the journal Science Translational Medicine that heralds a future in which a child’s genetic blueprint can be safely scanned for traits and defects long before birth by reconstructing the genome of a fetus using a blood sample from its mother and a saliva sample from its father. Before we all start screaming designer babies horrors, read the science and take a moment to take it all in. Then make your judgement.
Here comes the hardcore science bit:
I know some of you are thinking we know this is being done already right? Actually, originally, prenatal testing was conducted only to detect life-threatening disorders. Then, conditions such as Down’s Syndrome were added. Recently, British parents were given the go-ahead to test for cancer genes such as BRCA (this is important to note, as the cancer does not present itself until much later on in life). Furthermore, most prenatal diagnosis is done from a sample of either placental tissue or amniotic fluid, both of which must be obtained using invasive methods that can trigger miscarriage. Therefore, the fact that this much information can be obtained from a simple blood test and saliva is major in more ways than one.
So how is this possible? When a woman is pregnant, her blood contains fragments of DNA both from her genome and from that of her unborn child. Generally, around 13% of the DNA in her blood plasma — called ‘cell-free’ DNA — comes from the fetus. One of the biggest challenges facing scientist is telling the difference between fetal and maternal DNA (which is why invasive methods are required).
Step one: Jay Shendure, a geneticist at the University of Washington in Seattle, and his colleagues isolated 5 nanograms of cell-free DNA from a maternal blood sample taken at 18.5 weeks of gestation. They performed ‘deep sequencing’ on the DNA, which involved sampling fragments approximately 78 times. The researchers then went on to construct the mother’s genome by sequencing the DNA in her blood cells computationally using ratios to predict haplotypes and variants. Where the ratios diverged from what was known to be maternal (from a previous sample, before pregnancy), the reading was thought to be from the fetus genetic material. That sounds more complicated than it is.
Step two: Working out the fathers or paternal contribution. Here the researchers simply sequenced the father’s genome using DNA from his saliva (blood could also have been used but in this case was not available). Variants of his that didn’t turn up in the maternal blood were presumed not to have been inherited by the fetus; those that did were presumed to come from the fetus.
The third and most important step was to test the accuracy of the “constructed” genome. The researchers sequenced the child’s genome from cells collected from its cord blood after birth. Amazingly, they found out that they were able to predict inherited mutations using the parental samples reporting 98% accuracy. Furthermore, understanding that fetal screening needs to be done sooner to give parents time to respond, they then tested the technique on a second family with a 8.2 week-old fetus and obtained 95% accuracy (that’s half the amount of time as previous run). Job done.
As you can imagine the ethical bunnies are already jumping, and not without reason. Where do you draw the line when it comes to terminating a fetus due to a “known” disorder. Some scientist wonder how long it will be before traits such as albinism are considered defects that need to be screened out. So what does all this mean for the average person walking the streets?
Dennis Lo, a geneticist at the Chinese University of Hong Kong, who was the first to discover fetal DNA in maternal blood, argues that a better approach would be to target specific parts of the genome known to be involved in important genetic diseases. Sequencing everything, he says, will create serious ethical dilemmas. A important and valid point.
Hope you enjoyed the read and let me know what you think. Would you screen your unborn babies for genetic diseases in-order to terminate or to give yourself the opportunity to prepare yourself for the pressure having conceived a baby which needs special care? Financial strains? etc In the words of Dela Soul, The stakes are high.
Until next time. Have a great weekend.