Along with environmental confounders, specific alleles may also confound the relationship between epigenetic modification and outcomes. In this regard, recent research has demonstrated the existence of allele-specific methylation at up to 37% of heterozygous loci.[34,35] In this way, some alleles may be more likely than others to be epigenetically modified, independent of environmental exposures or outcomes. If these alleles are also more likely to occur at loci implicated in the etiology of diseases in question, independent of methylation status, such as the “s-type” allele of the serotonin transporter locus with respect to depression,[36] failing to adjust for genotype can result in spurious associations between epigenetic regulation and psychopathology.
