Last year, scientists successfully decoded the human
genome. The final blueprint was published exactly 50 years after
Watson and Crick discovered the unique, double-helix structure of
DNA. Decoding the human genome is one of the most significant
scientific breakthroughs of our lifetime, leaving the door wide
open for an exciting future for personalised medicine.
Imagine a consultation with your GP in the not too distant
future. Instead of making an educated guess about which medicine or
supplements you need and changing the dose according to how you
respond, your doctor will first check a sample of your DNA. This
will be collected painlessly from a simple cheek swab - or even a
fingerprint - rather than anything as antiquated as a drop of
blood. Once the technology is advanced, you will just hand over
your personal swipe-card on which your individual genome is
digitally recorded. Within seconds, your DNA will be analysed and
your doctor will know which drugs and supplements will suit your
individual genetic make-up. Such a test might predict how well you
will respond to a particular medicine or herbal treatment, what
dose you need and whether or not you would develop unwanted side
effects. Rather than the hit-and-miss approach of today, your
doctor will individually tailor your prescriptions for you.
Although this may sound far-fetched, much of the technology is
already in place and this rapidly evolving new branch of science
even has a name - pharmacogenomics.
The low-down on genes
Our genetic information is contained within molecules called DNA
(deoxy ribonucleic acid), the structure of which resembles a long,
spiral ladder. The rungs are made up of around three billion pairs
of sub-units known as nucleotides. Surprisingly, there are only
four different nucleotides, referred to as A, T, C and G, but the
order in which these sub-units occur along the DNA helix acts as
the code needed to make particular proteins. The code essentially
tells each cell the order in which to place amino acids when making
different protein chains. The stretch of DNA that provides all the
coding needed to make a single protein is known as a gene. We each
have around 28,000 genes within our DNA, which together make up our
individual genome. Each gene exists in many different forms within
the population, due to the exact order of its A, T, C and G
sub-units. Although we each inherit the same number and type of
genes, the subtle differences within them make each of us unique
from the other 6.5 billion people on this planet.
Since your genetic instructions differ slightly from those of other
people, the proteins you make from that genetic code also differ
slightly. Some of these proteins (which include enzymes) determine
how your body handles certain drugs - the way they are absorbed and
distributed throughout your body, how they interact with your cells
and how they are broken down and eliminated from your body.
That’s why some people do well with certain drugs while
others develop side effects. It all comes down to your genes.
It’s a Snip
The ability to link genes with drug reactions took a leap forward
in the late 1990s with the discovery of SNPs (single nucleotide
polymorphisms - pronounced ‘snips’). These one-letter
variations in the normal genetic code occur when a single
nucleotide in the DNA sequence has changed. For example, a section
of DNA within a particular gene might normally contain the
sequence: GATTACA, but someone might inherit a copy of that gene
which reads GAATACA instead - the first ‘T’ nucleotide
in the sequence has been replaced by an ‘A’. These
single variations, or SNPs, are common and at least five million
have been identified.
Most SNPs are benign and have no significant effect on the protein
coded for by that gene; they just act as a useful marker for
scientists to know which particular versions of a gene you have
inherited. A few SNPs can cause crucial changes, so that, for
example, an enzyme involved in drug metabolism no longer works
properly. This might happen because a different amino acid is
inserted when an enzyme is made, so it folds into a different
three-dimensional shape.
Because of the individual SNPs we have inherited, it is estimated
that many commonly used drugs, including aspirin, paracetamol,
ibuprofen, codeine and antihistamines, do not work in around a
third of people who take them. Millions, for example, do not find
codeine an effective analgesic as they have a particular variant of
a gene (called CYP2D6) which means they are unable to convert
codeine into its active form, morphine.
Another example is the cytochrome P450 family of liver enzymes
which are involved in the way our body processes up to 60% of
prescribed drugs and many herbal remedies (eg St John’s
Wort). These enzymes vary tremendously between individuals so that
some people metabolise these drugs poorly while others metabolise
them very quickly. In the future, knowing your CYP450 gene profile
will show whether or not a particular drug will suit you and
whether you need a high or low dose for an optimum result. Although
this sounds futuristic, the technology is already available to
screen for over 100,000 SNPs and predict how you will react to
certain drugs - whether you will have a good response, a bad
response or even no response at all. It is only a short step before
your GP checks your DNA prior to offering you a prescription. Truly
personalised medicine is on its way and will allow prescribing to
become less of an art and more of a science. SNPs have been
identified that show who will and will not respond to certain:
• cholesterol-lowering drugs migraine treatments •
anti-psychotics used in schizophrenia • medicines for heart
rhythm disorders • anti-asthma treatments • drugs for
Alzheimer’s disease • anti-clotting drugs.
Supplements
Your genetic make-up also means you will respond to supplements in
different ways. One of the most obvious areas to observe these
differences is in the treatment of joint pain - one reason why so
many different supplements are available. Some people find
glucosamine sulphate alone helpful to reduce such pain, while
others need the addition of other substances such as marine
chondroitin, MSM (methyl-sulphonyl-methane) and/or vitamin C for
optimum results. Just as when finding whether you respond best to
aspirin or paracetamol, you may need to chop and change to find the
right supplement combination and the right amounts for your
particular symptoms. Because taking glucosamine alone is one of the
cheapest options, I usually suggest someone starts with this first.
Then, if they are not entirely happy with the response after two or
three months, they can move up a level and combine glucosamine with
chondroitin, or MSM, or both. If you are satisfied with glucosamine
plus chondroitin alone, then there is no particular need to take
MSM too. If you feel there is still room for improvement, you could
add MSM to see if this provides additional benefit. If inflammation
is a particular problem, you might also consider omega 3 fish oils,
green-lipped mussel extracts or devil’s claw. It is not
always obvious which supplements will suit which people so you may
need to experiment with combinations to find the right one for you.
This will not always be the same one that suits your friends and
neighbours.
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