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Archive for December, 2015
In a consumer society junk is not any strange word. We have junk bond which is a high-yielding high-risk security, typically issued by a company seeking to raise capital quickly in order to finance a takeover. Junk food is similarly an ubiquitous word that is synonymous with obesity. What about junk DNA? Shouldn’t we look a little closer since we all carry it without being any wiser?
The completion of the first draft of the human genome sequence was announced to rapturous applause in June 2000 to those journalists gathered at the White House and at Downing Street. Craig Venter, who led one of the two teams of scientists that achieved this remarkable feat, said that having access to this information held “the potential to reduce the number of cancer deaths to zero during our lifetimes”. And President Bill Clinton claimed that “it is now conceivable that our children’s children will know the term cancer as only a constellation of stars”.
Fifteen years later, you don’t need to be a scientist to realise that this isn’t quite what has happened. So what went wrong? Are the huge promises made by Venter and others more rhetoric than reality, or is there still hope for personalised medicine?
Our genetic makeup is remarkable to say the least. We are wired for long winding march from our uncertain crawling to the present day with strengths and frailties. Progress we call it for so many visible leaps and bounds in our march. Myth of Prometheus is not merely about inventing fire but cooking which also can overload the liver from meat consumption. The bird picking on the liver of the Titan is a colourful description of liver disease from eating all those meat and at times indifferently cooked. Progress is to minimize the negative aspects of our present and maximize the plus points.
It is how we need look at genetic push for which we are carriers for the future. Your genetic code is unique to you, unless you are an identical twin. It specifies exactly why each part of your body is the way it is. But as well as controlling why your hair is brown and not black, variations to your genetic code also determine the risk you have of developing certain diseases, and why you might respond well to some drugs and not others.
The publication of the human genome sequence at the turn of the century heralded a new era of medicine, where therapies would be tailored to each person’s unique genetic code, making indiscriminate and damaging treatments like chemotherapy a thing of the past.
So, if the technology is available to sequence everyone’s genome, why don’t doctors now ask for a DNA sample as part of a routine diagnosis?
Not all junk DNA is rubbish
It’s because, over a decade after the first draft of the human genome was published, we still really don’t have any idea of what most of it actually does.
One of the most surprising outcomes of the completion of the first draft of the sequence was that there are far fewer genes found in the junk DNA. So now we scientists have a major problem. We can sequence a patient’s genome efficiently and economically, we can process the data rapidly, and we can identify changes to the DNA that are associated with the disease in question. But, in most cases, we have no idea how those changes cause the symptoms of the disease.
Cracking the code
There is now a major drive among researchers in the genomics field to develop tools to address this issue. It is known that one thing harboured in this junk DNA are switches that tell certain genes when and where in the body to turn on (this is why you only have one nose, and don’t start sprouting eyes on your elbow).
It is also known that many disease-causing changes to your DNA are found within these switches, so that a given gene doesn’t turn on or off at the right time, or turns on at the wrong time somewhere in the body where it shouldn’t be active. If the gene in question controls how cells grow, the result of the broken switch can be cancer.
However, identifying these switches and linking them to the genes they affect is not a trivial task. It requires enormously complex experiments with rare and precious tissue samples donated by patients, and then a vast amount of computing power to sequence, analyse and interpret the results.( ack: Bryony Graham of Univ. of Oxford-the conversation,Dec.2,2015)