I've yet to read it in detail, but a quick scan reveals dozens of genes which have been shown to have small cumulative impacts on IQ (with average differences between various alleles being in the two to four point range). The most significant difference I saw was between the two versions of the ADRB2 gene. In humans there exists two non-synonymous coding SNP's (rs1042713 and rs1042714) for this gene. The 713 version conferred a whopping eight point increase in average verbal IQ.ADRB2 is more commonly known as the beta-2 adrenergic receptor, which is activated by adrenalin and noradrenalin (also known as epinephrine and norepinephrine). Even though the primary role of the receptor is regulation of smooth muscle relaxation, the receptor is also expressed in the central nervous system, and some studies have suggested that it plays a role in memory and learning formation. Interestingly the rs1042713 allele is a human-specific variant differing by a single amino acid from the "ancestral" protein sequence.
But does that really mean we've cracked the code for the genetic basis of intelligence? Not exactly. While there was an 8 point verbal IQ difference between individuals that varied at this allele, the author cautions that there could be "possible inflation of the estimated genetic effect sizedue to the relatively small sample size." Also, because intelligence appears to be affected by many genes it is unknown whether variation of the beta-2 adrenergic receptor sequence would have the same effect in all genetic backgrounds. And, of course, the question of whether the sequence variation affects the receptor's function in smooth muscle tissue has not been addressed. But that's the nature of scientific research. No one study provides all the answers, and this particular study points to an interesting direction for follow-up research.
Someday we may look back and indeed acclaim Gosso's research as a turning point in human genetic research. Only time - and further experiments - will tell.
Note: I did a search of PubMed and this portion of Gosso's thesis does not appear to have been published yet.
Image: 3D representation of the beta2-adrenergic receptor (via Science).