Monday, March 28, 2011

Breaking News: Chinese dopamine genes not-confirmed

Finally some evidence that stuttering research is actually following the scientific method. In a highly unusual move, Drayna's team has actually tried to replicate a study rather than churn out new stuff. They looked at the Chinese gene study, and could not replicate the study.

Kanstantsin made me aware of this new study (that was probably finished years ago but only now published! So the wider community was deprived out this valuable information despite Drayna being funded by the publicly-funded NIH). He writes:
Drayna is one of the authors. of "Evaluation of the association between polymorphisms at the DRD2 locus and stuttering."

They basically tried to replicate the 2009 study from chinese group (I think you blogged about it). [Yes, I did in More Genes from China!] "Association between dopaminergic genes (SLC6A3 and DRD2) and stuttering among Han Chinese."
In that 2009 study chinese researchers found asociation between one form of DRD2 gene (dopamine receptor gene) and stuttering.

So in this new study, Drayna & co also tested DRD2 gene and used bigger sample and tested europeans and brazilians; and they did not find any correlation that was observed by chinese group. They also note that in chinese study, the variant of DRD2 gene claimed to be associated with stuttering was not only found in 96% of PWS, but also in 88% of controls, so it probably does not have any significant effect on stuttering.

...It looks like so far only mutations of some lysosomal genes were clearly shown to be associated with stuttering (or at least with some forms of stuttering in some people).
We cannot exclude that the Chinese stuttering genes are not present in European or Latin America people. However, they only found a 96% to 88% ratio, which make me very sceptical. In fact, I should have noticed this weakness in their paper, and report on it. That teaches me (and all of us) to actually read the whole papers carefully word by word, and not just the abstract.

Moreover, the dopamine imbalance theory propagated among other by Jerry Maguire has lost a vital empirical ally. He is left with his PET study, that as far as I know has not been replicated yet.

Needless to say, that the strategy to find signals in statistically significant differences, like 96% to 88% ratio, is precisely what stuttering research does. And needless to say that most would go away in attempts of replication. But luckily that is not better done, so the pseudo-scientific researchers are still doing fine.

So who will non-replicate Drayna's lysosomal results? Note that here I did point out some Xi Square statistical weaknesses. ;-)


Anonymous said...

so you don't think that stutterers have higher levels of dopamine?

Tom Weidig said...

@Anonym: I just don't know. I always wondered why such a high level of dopamine would only affect speech? And what about the structural abnormalities? Moreover, it might not be the high level that is crucial but an abnormal level (i.e. too high or too low), or it could be the ratio to other neurotransmitters.

What I do know is that the empirical evidence is weak.

Unknown said...
This comment has been removed by the author.
Unknown said...

Dear Tom,

In p. 92 of my thesis, "Computational modeling of the neural substrates of stuttering and induced fluency" (, I suggest why such a high level of dopamine would only affect speech. Moreover, during brain development, high dopamine levels may possibly cause the structural abnormalities.

Oren Civier, PhD
Cognitive and Neural Systems

Anonymous said...

Very very very weak Evidence!!!

Only 3 stutterers tested in the Dopamine Hypothesis paper....j/k

3 stutterers and 6 non-stutterers, unequal balance!!!

NextTime said...

Next time, let's not censor the comments, please. We the reader deserve to hear all sides of the story. Who knows if Drayna posted a comment that you didn't like or Mark Onslow. Like you said, leave the comments and let the reader decide. When it is deleted....we don't know. PWS are not stupid.

Eric said...


Thanks for your link to your thesis. I read the whole thing and found it very interesting and plausible in explaining the etioligy of stuttering.

Most interesting to me was the explanation of 'blocks' and how and why they are possibly caused and the relation to the processes and physiology of the brain.

One reference in your paper on MPI also piqued my interest. I have never heard of that before and on doing some quick research on the subject, it seems to be an effective therapy.

Tom - Maybe you can do a post on MPI?

Oren - Again, thanks for your contribution.


Paul said...

Tom, I always wondered how zero gravity in space would affect our speech? Would it be possible that some people’s brains are affected by the earth’s strong magnetic field, I mean this staff is all around us right? How do we know that magnetic field does not have a negative impact on some people neurological factors? I wonder how stuttering condition would behave in space away from earth’s magnetic field. At the end I don’t think it was ever tested in outer space right. What is your take on this?