Schizophrenia and genetics

There was an interesting news item yesterday on the BBC news site about schizophrenia and genetics1.  The story reports on an article published in Nature, which is the write- up of a large research project into the genetic dimension of schizophrenia. According to the story, scientists have found more than 100 genes that make people ‘more susceptible’ to schizophrenia – 83 of which have never been pinpointed before.  Many of these genes are involved in the relay of chemical messages around the brain, whilst others are involved in the immune system.

The article quotes Professor David Curtis of University College London, and part of the research team, as saying: ‘This study puts psychiatry into the same category as other parts of medicine’.  He goes on to say: ‘Now we show with confidence that there are biological processes going awry.’

At this point however, we need to be careful.  Claims regarding the biological basis of schizophrenia have been around for years, and have been deeply contested – not only by those who might have a vested interest in debunking such ideas (including psychoanalysts!) but, more significantly, by geneticists themselves.

And the arguments over schizophrenia are part of a wider debate which is often framed in terms of ‘nature versus nurture’.  In other words, how much does biology (‘nature’) contribute to the development of particular types of mental illness, and how much does a person’s upbringing and wider social environment (nurture) contribute?  In reality, though, most psychiatrists and other mental health professions would accept that it’s not an ‘either or’ but rather some of each.

One of the problems with these kinds of debates, as exemplified by the BBC story, is that as soon as biology enters the equation the assumption is often made, especially by journalists and other non- scientists, that somehow this settles the argument.  In other words, if it can be shown there is a biological dimension to a mental health problem then this ‘proves’ that such a problem is ’caused’ by biology, in this case faulty genes.

In this particular case, there is a further implication, with respect to Professor Curtis’ claim about the study putting psychiatry on the same footing as other parts of medicine, that other (physical) illnesses are biologically based, i.e. that they are ‘real illnesses’.

The problem is, this is both bad logic and bad science.  To start with, it’s not clear what constitutes a ‘real’ illness.  From this article one would assume that it’s an illness that can be shown to have a biological cause.  One of the problems with this argument, however, is that it effectively sets up a ‘straw man’, i.e. that there is a dichotomy between ‘mental’ and ‘physical’ illnesses, and that ‘physical’ illness are ‘real’ whilst ‘mental’ ones are not. However, I for one would argue that there is a biological dimension to all ‘mental’ illnesses; but this does not make them any more or less ‘real’ than ‘physical’ ones.  Both ‘physical’ and ‘mental’ illnesses are multi-dimensional, i.e there are always multiple factors involved in any illness.

But this brings us on to another problem, which relates to the question of cause.  And as any philosopher of science will tell you, the notion of ’cause’ is a notoriously tricky and slippery one.

Most studies that claim (or imply) a genetic cause for a particular illness are based on statistical analyses of groups of people: normally one group that has the disease and another (the control group) which doesn’t.   There are often elaborate controls in place to ensure that other factors, for example environmental ones, can be discounted.

But what these statistical analyses show are not causes but statistical correlations.  In other words, that there appears to be some kind of relationship between, in this case, genetic make-up and the particular illness under investigation.  However, what these studies do not (and some would argue cannot) show is causality, i.e. that one thing causes another, in this case that faulty genes cause schizophrenia.

Perhaps the sub-text of the article is the real giveaway: it quotes Dr Gerome Breen of King’s College London as saying: ‘We now have a massive amount of new biology to investigate……This is crucial.  Drug therapy for schizophrenia has not changed significantly since the 1970s’

Presumably then, the pharmaceutical companies will be showing more than a passing interest in this story…………?

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