She took 35 "neurodevelopmental" disorders, ranging from rare genetic syndromes like Rett's, up to autism, ADHD and specific language impairment (SLI), and compared their prevalence stated in a textbook, to the number of scientific papers published about them over the past 15 years.Note that with something like Rett's, there's no question that they're problems with brain development. With autism, some people would contest that but not many nowadays. With ADHD and some others, however, it's pretty controversial. Bishop includes them on the grounds that they're generally treated as neurodevelopmental in the scientific literature.
The graph above - which I should stress is mine; Bishop's are much less messy - shows the basic results.
First up, there's a correlation between prevalence and the number of research publications, but as you can see, it's pretty weak. Within the rare genetic disorders (pretty much everything below 0.1% prevalence) there does seem to be a relationship. When you get to the more common disorders, which are also the ones which are more controversial, there's no correlation at all.
Some points stand out:
- Autism is very popular; it gets the same amount of research as intellectual disability aka mental retardation (ID/MR), even though ID/MR is 9 times more common (0.65% vs. 5.5%)
- Down's Syndrome gets a huge amount of research despite being rare. It gets much more than Cerebral Palsy and Fragile X despite them all being severe and roughly as common.
- Tourette's is much less studied than any other disorder with a similar prevalence.
- In the bottom left you'll see a bunch of apparantly very common disorders like dyslexia, dyscalculia, and specific language impairment, which are extremely under-studied... if you accept those prevalence figures.
As for why all these figures are they way they are, it's less clear. Bishop discusses various factors like severity and the availability of funding in the paper, but this can't explain everything. It seems likely that some things are just more scientifically fashionable than others, for whatever reason...
Link: See also Bishop's Guardian piece about the paper.
Bishop DV (2010). Which neurodevelopmental disorders get researched and why? PloS one, 5 (11) PMID: 21152085
7 comments:
I wouldn't discount the funding issue. There is a *ton* of private foundation money right now for Autism. Of course, it helps that there are lots of interesting intellectual questions as well.
I wouldn't be surprised if tractability of the disorder plays into it. Down's has a clear cause (trisomy 21) and phenotype and it's clear that ADHD can be treated with drugs. On the other hand, Tourette's is highly variable in it's presentation, and dyslexia, dyscalculia, and SLI are incredibly difficult to treat and fairly variable in presentation.
That doesn't explain autism, of course.
We autists are the most interesting, that's why :)
this report is interesting to consider with Francis Collins' efforts at the NIH to implement programs that would make translational therapeutic research more accessible (cures acceleration network; CAN), and more productive. with such programs that aim to support research of diseases with a small market base (therapeutics for rare and neglected diseases; TRND), conditions like Fragile X may see a bump in publications.
with that in mind, quality of life seems to be somewhat of a determining factor.
I think, like Jeff says, it is about tractability. Intellectual disability doesn't even pretend to be anything other than an instrumental definition and no one thinks it picks out any particularly uniform diagnosis and the aetiology is known to be diverse. Therefore studying it is likely to be less fruitful from a scientific perspective. And the perfect example of that is that Down's syndrome is just one of the many causes of intellectual disability.
Tractability is a tricky issue though, because how do you know how tractable something is until you really have a good crack at it?
And a problem which is too tractable, will end up not having as many papers as one which is messy, because mess provides material for more papers. Maybe not better papers but certainly more.
Hmm, possibly, but it is certainly the case that people are not going to be keen on starting a research programme into a fairly nebulous concept like 'learning disability' if you're looking for, say, genetic causes or neural substrates.
As I intimated above, Down's syndrome is a cause of learning disability - so it can't be prejudice against learning disability per se that causes there to be less research.
A quick pubmed search reveals there to be 4x more papers on IgA nephropathy compared to acute glomerulonephritis despite the former being a cause of the latter.
I think it makes perfect sense that, apart from certain specific reasons, you will choose to investigate the pathologically homogeneous subset of the larger category where possible.
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