I note that there has been at least one negative finding for the same gene:
"No Association Between Cholinergic Muscarinic Receptor 2 (CHRM2) Genetic Variation and Cognitive Abilities in Three Independent Samples."
http://www.medicine.manchester.ac.uk/research/PubDetails/index.aspx?ID=37741
The study appears to be looking at SNPs - though it tracks quite a number of them. Possibly the relevant variation has a geographic component.
Link.
"Razib Khan has an academic background in the biological sciences, and has worked for many years in software. He is an Unz Foundation Junior Fellow. He lives in the western United States."
Razib's writings can be found on his blog, Gene Expression.