In contrast, the CpG island surrounding Exon 1 has only been recently described and its role in illness is completely unknown. However, since the amount of variance in mRNA and protein production accounted for by the 5HTTLPR is relatively modest (i.e., <10%) [Hranilovic et al., 2004; Bradley et al., 2005], it is reasonable to assume that other cis and trans acting elements in the greater SLC6A4 gene region, such as the CpG island, constitute the majority of the regulatory mechanism(s) controlling SLC6A4 activity. Because the protein product of this gene is a key target of antidepressants, the complete delineation of these and other regulatory elements in this gene could substantially advance the development of an integrated understanding of the pathogenesis of common behavioral illness.
