In the beginning was the word and the word was ACGT – life encoded in combinations of three out of a possible four nucleotides; Adenine, Cytosine, Guanine and Thymidine.  This year is the 10th anniversary of the sequencing of the human genome.  At a stroke, it would appear,  a new perspective on health and disease has opened up.  By comparison of genomes from different individuals, it may be possible to identify the risk of getting disease and, armed with that knowledge, make the necessary changes in diet, lifestyle, and exposure to chemicals that would reduce it.  

But genes encode for proteins, not for diseases.  But we only know about defects in specific proteins in a few rare diseases.  In Duchenne muscular dystrophy, for example, there is a defect in the synthesis of a key protein known as dystrophin.      

Common diseases like irritable bowel syndrome are likely to be the end result of an interaction of a number of factors, each with their own genetic and environmental regulators.  And since IBS overlaps with other diseases as well as anxiety and depression, any genetic component will most probably encode for a protein incorporated in some generic factor involved in visceral sensitivity or emotional reactivity.  In addition, genes may predispose to an illness but only in combination with other genes and changes in the environment brings that tendency out.  For example, environmental change induces growth and connection of nerve cells by regulating gene expression.  And this can affect every system in the body.  It’s all very complicated.  Any advance in knowledge rarely provides simple answers, just a vast array of unforeseen questions.  

Only 1% of the genome encodes for specific proteins, about 20,000 of them – the same number as in a nematode worm.  Ten times as many are regulator genes, that are turned on and off by environmental factors and modify the expression of certain genes.  Anything that changes the expression of transmitters, modulates intracellular machinery, and induces growth and cell division will involve regulator genes.  These then are the targets for treatment and prevention.  The remaining 90% of the genome is thought to be junk, DNA fragments, stuff left by some viruses.  Scientists have found no use for it as yet.  Genetics, like human life, is a bit of a mess, not unlike the hard drive of your computer, which contains bits of everything you’ve deleted or copied. 

So the sequencing of the human genome hasn’t resulted in the dramatic breakthroughs that were expected.  Part of the problem is that it takes a long time to sequence the genome from a single individual and everybody’s genome is different.  At the moment, gene sequencing is rather like tearing a book up into fragments of page,  sequencing these and then putting them together again, but with new methods of sequencing coming on stream, things will be much quicker.  In five years time, the cost of sequencing somebody’s genome will be as little as £1000 and we will have a much better handle on the nature and function of the regular genes.  Then comparison of genomes from people with IBS will be feasible.  But will we be any closer to finding a cause  …… or an answer?

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