rs855791

rs855791 is a missense variant in TMPRSS6 causing a valine-to-alanine substitution at codon 736 (Val736Ala) in matriptase-2, a liver serine protease that normally suppresses hepcidin production. The 736Ala allele inhibits hepcidin less effectively than the ancestral Val form, so carriers tend to have lower hepcidin and correspondingly higher serum iron, transferrin saturation, and hemoglobin/erythrocyte indices, while the reverse holds for the Val allele. Alongside TF rs3811647, it is used to estimate genetic tendency toward lower or higher iron status within the normal range, distinct from clinical deficiency or hemochromatosis.