BACK in June 2000, when Bill Clinton triumphantly announced the working draft of the human genome, it was tempting to believe that we would soon be masters of our own genetic make-up. Tempting but entirely wrong. Five years on, most of the profound possibilities stemming from the human genome project appear as far away as ever.
Take pharmacogenomics, the idea of tailoring medicines to an individual鈥檚 genetic make-up. It was always going to take time to develop: identifying which genes act to alter a drug鈥檚 impact on metabolism is a painstaking process, made still more complex and time-consuming by the fact that often several genes are implicated. As we head towards these horizons, much of what we discover threatens to push back still further the time when we can expect to understand what we are really dealing with. For the same reasons, and despite recent hype, diets tailored to genomes 鈥� or nutrigenomics 鈥� will not arrive any time soon.
But there are some fascinating hints of what may be in store. Last week, researchers reported finding a gene that codes for two hormones which act against each other: one suppresses appetite, the other stimulates it (see 鈥淭he gene that can make you feast or starve鈥�). Control over which of the two proteins is produced rests not in the genome, nor in the ribosome where they are made, but with enzymes that subsequently tweak the proteins according to some as yet undiscovered regulatory process. The driving force in this case appears to be the proteome, the massed ranks of interacting proteins within the body. The proteome was always known to be larger than the genome, and as estimates of the number of human genes has fallen 鈥� it now stands at about 25,000 鈥� so the proteome has grown in importance.
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However, the proteome is not the end of the story either. A Canadian group announced this week that a gene can be silenced in rats simply by giving them an amino acid, methionine (see 鈥淗ow the food you eat could change your genes for life鈥�). Genes can be deactivated by adding methyl groups to their DNA, and in this case it seems likely that the methionine is donating methyl groups that makes this happen.
While this is not the first food found to exert such 鈥渆pigenetic鈥� control, it is especially interesting because it radically alters the behaviour of the rats. The hopeful implication of this work is that, with the right food supplements, we will be able to switch genes on and off at will to treat both physical and mental illness.
These studies show up the exquisite complexity of the human body and hint at the control we may eventually exert. But most of all, they highlight how far we still have to travel before we really understand what makes us what we are.
