Again, a completely unrelated search unearthed an interesting paper. This time it really is a piece of Google archaeology, since it has zero citations according to ISI -- just a dead end so far. The paper is by Mark G. Thomas and colleagues, in the journal Intelligence from 1998; here's the abstract:
Recently a mitochondrial DNA polymorphism (EST00083) was found at significantly different frequencies in high IQ and low IQ groups in two independent studies. We have used mitochondrial sequences from a range of populations to show that this polymorphism occurred more than once in human history. Furthermore, the polymorphism is particularly common in Europe where it is predominantly associated with a single mitochondrial line (lineage) that appears to date back to the expansion of anatomically modern humans into Europe about 35,000 years ago. Examination of the genetic diversity within this mitochondrial lineage, together with the known migration and settlement of Europeans into the USA, suggests that the observed IQ associated polymorphism found in Cleveland Ohio is likely to be restricted to only one form (sub-group) of this mitochondrial lineage.
And there's this in the introduction:
Considering the central role that mtDNA gene products play in the energy metabolism of the cell, a causative link between mtDNA mutations and cognitive ability remains a strong possibility. Apart from the existence of a number of neuro-degenerative diseases associated with mtDNA lesions (Wallace, 1992; Shoffner & Wallace, 1994), there is a case in which a patient's IQ was found to increase by 20 points upon treatment for mitochondrial dysfunction (Anezaki, Yanagisawa, Ibayashi, & Miyatake, 1992) (Thomas et al. 1998:171).
The marker is a restriction site deletion that is fairly common in Europeans and less so in East Asians; they conclude that if there is a real QTL for intelligence on the mtDNA, it is likely not carried by all the variants with this marker, but instead only a subset. Is it real? How old is it? How common?
Oh, and as for that 20 point increase in IQ after mitochondrial treatment? That paper was only cited once -- by this one.
Thomas MG, Miller KWP, Mascie-Taylor CGN. 1998. Mitochondrial DNA and IQ in Europe. Intelligence 26:167-173.