Month: January 2009

Premature conclusions

Something the media is very good at, and alas some scientists too, is making a conclusion about a scientific investigation before actually performing the investigation.

This is not how science works!

A recent example of this appeared in today’s Daily Mail, the popular gutter-rag that leads the way in pseudo-scientific sensationalism:

Women who drink coffee or tea during pregnancy may increase their baby’s odds of developing cancer, doctors believe.

Experts say caffeine may damage the DNA of babies in the womb, making them more susceptible to leukaemia, the most common cancer in children.

To establish the link, scientists at Leicester University will scrutinise the caffeine intake of hundreds of pregnant women and compare the results with blood samples from their babies after birth.

Researcher Dr Marcus Cooke said there was a ‘good likelihood’ the study would make a connection. Previous research has shown that caffeine damages DNA, cutting cells’ ability to fight off cancer triggers such as radiation.

Changes of this kind have been seen in the blood cells of children with leukaemia. Scientists know they occur in the womb, but do not know why.

‘Although there’s no evidence at all of a link between caffeine and cancer, we’re putting two and two together and saying: caffeine can induce these changes and it has been shown that these changes are elevated in leukaemia patients,’ added Dr Cooke.

So, they’re planning to investigate this link, though Dr Cooke is quoted as (apparently) saying there is a ‘good likelihood of making the connection‘, despite, as he is later quoted, there being ‘no evidence at all of a link between caffeine and cancer’.

Dr Cooke is also quoted as saying that ‘previous research has shown that caffeine damages DNA, cutting cells’ ability to fight off cancer triggers such as radiation‘; now, I am not going to judge Dr Cooke on the basis of such quotes, because I well know how much gutter-rags like to quote out of context, but I can’t help wondering whether this prior research was a case of caffeine being introduced to cells in a dish, rather than to an actual living and breathing mammal. Any number of chemicals can cause physiological disturbance to cell cultures, but these do not necessarily translate to their being harmful to us generally.

So what’s my problem?

Continue reading “Premature conclusions” →

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The same, but different…

Epigenetics is a term that is being bandied around quite a bit in the biological literature these days. It is not a new term, but in its current definition the term is used to term heritable changes in gene expression that occur without changes to the DNA.

So what does this actually mean? Well, most people will be familiar with the fact that DNA provides the blue print for how an organism is put together, and that over time mutations in the DNA can change certain properties of what that organism looks like; or they may result in a genetic disease, such as cystic fibrosis or sickle cell anaemia.

However, how do we explain the phenomenon wherein sets of identical Human twins, whom share identical DNA, one twin can develop schizophrenia, pancreatic cancer or diabetes, whilst the other remains unaffected? If we were interpreting their development on the basis of their DNA sequence only, then we have a conundrum.

The answer is that DNA is involved in a dynamic, interpretative process. For example, you may buy a new computer, and in this computer there is a graphics chip that is controlled by a piece of software called “firmware”. This software tries to get the most out of the hardware. Every so often, a new piece of firmware is released, and sometimes it can revolutionise the function of that graphics chip. The chip hasn’t changed, but the software has. This is not a perfect analogy, but what I want to convey is that sometimes the hardware doesn’t need to change; sometimes you can just change the way it’s used.

Thus, the sequence of bases of DNA does not necessarily have to be altered for a new effect to be seen in the resulting organism; some changes can occur by epigenetic processes. There are several different types of epigenetic process, and these differ depending on whether we are speaking about high organisms, such as Humans, or single-celled organisms, such as bacteria.

At the simplest level, one such epigenetic change might be a process call methylation; in this, a chemical group is literally tacked onto the DNA at a certain sequence, which can result in a change of gene expression. If a gene is seen as a piece of DNA that results in a functional product, then we can start to see how changing the level at which this product is produced can have an effect.

One of the recent and interesting findings about such epigenetic changes is that they too can be inherited, leading to questions about the nature of “genetic memory”, the idea that the lifestyle lead by your grandparents can have had a direct effect on the way that your DNA expresses its instructions. In the example of the twins, once identical twin embryos have separated, each cell division can result in the accumulation of an increasing number of these epigenetic changes, adding up to quite a difference over a life-time. Thus even things that are the same can be different.