Relationship Between SNP rs1617640 and the Erythropoietin Gene. The SNP is located 1,125 bp upstream of the EPO transcription site. The findings of Tong, et al. suggest an additive allele-dose model with the heterozygous risk allele being GT and the homozygous risk allele being TT. The T allele appears to enhance EPO expression by creating a matrix match with EVI1/MEL1 or AP1 transcription enhancer binding sites.To simplify the Figure, the region of EPO containing the coding sequence is illustrated by the uninterrupted yellow rectangle and is not drawn to scale. The blue rectangle represents noncoding sequence upstream of the EPO start site and is not drawn to scale.