TMPRSS6 (Transmembrane Serine Protease 6): TMPRSS6 is a protein that plays a key role in regulating iron metabolism, primarily through the control of hepcidin — the hormone that governs iron absorption. Mutations in TMPRSS6 can cause iron-refractory iron deficiency anemia (IRIDA), a form of anemia that does not improve with oral iron supplementation.