CHRM2 gene SNPs in introns 4 and 5 associate strongly with intelligence. rs2061174 A allele increases adult PIQ by 6.89 points. rs324650 T allele increases child VIQ by 5.30 points. Associations confirmed in Dutch twin families using family-based tests. Dense SNP coverage rules out other CHRM2 regions for IQ effects. rs324650 lies in human-specific MIRb SINE repeat. CHRM2 best replicated gene for normal intelligence variation. Gene involved in neuronal excitability and synaptic plasticity. No genotype-dependent CHRM2 expression differences in parietal brain. All six CHRM2 isoforms expressed in human brain. Previous studies replicated including Comings 2003 and Dick 2007. Associations free from population stratification via within-family tests. IQ measures normally distributed and standardized for age and sex. Young cohort mean age 12.4, adult 37.6. Findings point to regulatory variants in 5'UTR regions.