Tuesday 7 June 2011

The finger length ratio

Apparently 2012 has been forecast to be quite a year for us humans. Depending on what you read (and believe), we are either destined for total annihilation or some population-wide transformation. For those of you who saw the recent Hollywood blockbuster 2012, it might be a good idea to book that space vacation fairly soon. Or maybe not...

I have to say that I have never really been one for the various methods suggested to predict our future. With my science hat on, the notion that we can 'see beyond' has never really excited me despite my openness to things like precognition (see the recent study from Daryl Bem for a more science-y take on this). Indeed, even if anyone were to be able to provide some experimental evidence for such an ability (and it is a big 'if'), I would have thought the first thing they would have done is pick the winning lottery numbers or failing that at least make some money on predicting things like the winner of the Eurovision Song Contest (now that would be some feat). If that person didn't personally want to financially benefit from the proceedings, they could always give the money to charity; in the current economic climate, there is most definitely a need.

One area in the whole 'future-reading' game has however been of perhaps slightly more interest to me: the idea that our hands may provide some clues to our future, at least our future health. I say all of this because of this study recently published, and picked up here, which suggests that finger length (ratio) may correlate with a form of motor neuron disease (amyotrophic lateral sclerosis, ALS). The study is an interesting one, in that researchers found that a low index finger to ring finger (2D:4D) ratio was significantly associated with ALS compared to controls (p=0.007). They further go on to link the findings back to an old friend, testosterone, and more specifically high prenatal testosterone exposure.

I have touched upon testosterone in relation to autism a while a back but did not go in to the detail. Testosterone and autism have been in the news of late following some focus on the use of the 'lupron protocol'. I will say no more on this particular issue. The basic theory is that autism is an example of an 'extreme male brain', whereby people with autism are hyper-systemisers, as opposed to empathisers. Systemisers are great at things like computers, engineering and map-reading abilities but not exactly great material for being a Priest / Vicar. Likewise I wouldn't necessarily put that great empathiser in charge of building your new skyscraper.

The reason put forward for such a male brain: elevated testosterone levels in-utero.

How do you measure such exposure? Well the digit ratio among other things has been put forward as quite a good correlate. What are the findings in relation to autism I hear you say? There is some evidence that autism follows the trend of low 2D:4D finger ratio potentially indicative of elevated prenatal testosterone exposure. I can see why the whole theory is so attractive. It is quite a simple theory (testosterone exposure = different way of thinking) and importantly, easily testable. The evidence base is quite large; and in terms of autism, bridges the gap between listed psychological/behavioural symptoms, physiological findings and even providing some information about possible transmission of autistic symptoms.

Having said that, there are a few issues with the theory which perhaps merit some discussion. First and perhaps foremost is the 'universality' of the theory to 'all' cases of autism. I think most researchers who set out to research/investigate/examine autism start in the same naive way that I did. You read the various research papers and textbooks which more often that not give you this impression that autism is autism (one condition with a few diagnostic variants) and from that you organise your research studies to look at autism as some kind of singular entity, comparing autism for example against not-autism controls (even this has issues), and if you are lucky a group like learning disability. The reality however as you progress through your career and wisdom starts to seep in, is that autism is very much not a singular autism, but rather autisms; and accompanying those autisms are as wide a variety of co-morbidities as you would expect to find in the not-autism population.

I started this post talking about finger ratio and risk of ALS. Wait a minute, low finger ratio and ALS, low finger ratio and autism. Does this mean that people with autism are at greater risk of motor neuron disease? Or on the flip-side, people with motor neuron disease for autism? There might be a familial possibility but I am pretty sure that ALS is not a significant co-morbidity to autism unless you perhaps factor in environmental exposure. Aside from the various papers suggestive of a relationship between (female) sexuality and finger ratio, finger ratio has also been linked to stock trading, athletic ability and risk of arthritis (the osteo- variety). Quite out of the blue, I also found this paper suggesting that latent toxoplasma infection might also show some involvement following on from my previous posts on T gondii and its potential 'mind controlling' effects (at least in the rat model).

I don't want to seem to negative on the whole finger ratio hypothesis. I am not saying that the 2D:4D ratio might not represent some effect in some cases of autism. The primary problems I have is when such effects are generalised to an entire population and potentially at the expense of an effect outside of the core condition.

Horoscope anyone?

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