One of the most important common findings in these 3 previous SLC1A1 studies was a haplotypic association in the 3′ region of the gene.16-18 Our results are in line with this observation, as 2 of the 3 SNPs of the associated haplotype we identified are located in exon 10 and the 3′ untranslated region. The third SNP of this haplotype, however, lies somewhat upstream (intron 2) of this region, and although all 3 SNPs (rs7858819, rs301430, and rs3087879) were in considerable linkage disequilibrium with each other (Table 1), we speculatively interpret this observation as evidence for more than 1 functional locus within SLC1A1, as has been suggested previously.17,18 Additional support for this tentative conclusion stems from another SNP, rs3933331, located farther upstream and clearly not in linkage disequilibrium with the previously mentioned haplotype markers that we found to be associated with gene expression functionality and that predicted an OCD hoarding subphenotype in our sample (Figure 1 and Figure 2). The possibility of 2 or more functional (possibly causal) variants of differential effect size provides 1 plausible explanation for the molecular
