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."
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.
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).
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. ;-)