Polymorphisms in the Transferrin 5′ Flanking Region Associated with Differences in Total Iron Binding Capacity: Possible Implications in Iron Homeostasis

We have identified five single nucleotide polymorphisms (SNPs) upstream (5′) of the transferrin coding region. One polymorphism is in the 5′ UTR at nt +49, and four are in the promoter region at nt −34, −551, −617, and −739, numbering from the start of transcription. The −34 and −617 SNPs are tightly but not completely linked. The −34 polymorphism lies between a conserved Sp1 site and the TATA box. The −617 polymorphism is within the DRII enhancer region. Five haplotypes have been defined from these SNPs by the identification of at least one homozygous individual, and two other haplotypes were deduced from heterozygous individuals. The total iron-binding capacity associated with each transferrin haplotype was haplotype 2 > 1 > 4 > 3. Transferrin promoter haplotype 2 had a significantly higher mean TIBC and haplotype 3 had a significantly lower mean TIBC than the more common haplotype 1. Persons with haplotype 4, which includes the −34T and −617A minor alleles, have a lower mean TIBC but the difference was not statistically significant. In normal individuals, the differences in the haplotypes were not found to be associated with differences in transferrin saturation and ferritin levels. There was no difference in the extent of increase in the mean TIBC levels in individuals with iron deficiency anemia in regard to their haplotype. Furthermore, there was no difference in the relative frequencies of the transferrin haplotypes in the iron-deficient population. In hemochromatosis patients who were homozygous for the C282Y HFE mutation, no particular haplotype was associated with a significant difference in transferrin saturation or ferritin levels. In White patients with Parkinsonʹs disease, a disorder in which there is abnormal iron deposition in the brain, the presence of transferrin haplotype 3 was in slight excess over the normal White population.