SNPs in the SNAP25 gene were initially [PMID 17160701] linked to intelligence but have failed to replicate [PMID 19418213].
While now suspect, the original work can be found in [PMID 16801949].
The (T;T) genotype averages almost 3 PIQ points higher than the (C;T) genotype, which averages almost 3 PIQ points higher than the (C;C) genotype.[PMID 17908175]
rs353016 is in close linkage with rs363050, with r2 = 0.98, such that the rs363050(A) allele typically is linked to the rs353016(T) allele. For SNPs rs363039 - rs363043 - rs353016, respectively, the haplotype C-T-T is most associated with higher intelligence in children, whereas the haplotype C-C-T is most associated in adults (SNPs oriented as in dbSNP). [PMID 17908175]