CYBRD1, also known as Cytochrome b Reductase 1, is a gene encoding a key enzyme involved in iron metabolism. It functions primarily in duodenal enterocytes, where it reduces dietary ferric iron (Fe³⁺) to the more soluble ferrous form (Fe²⁺) at the brush border membrane. This reduction step is crucial for the subsequent uptake of iron into the body via the divalent metal transporter 1 (DMT1). CYBRD1's activity is therefore essential for maintaining systemic iron homeostasis, and its expression is regulated by body iron stores and hypoxia. Dysregulation of this gene has been implicated in disorders of iron overload, such as hereditary hemochromatosis, highlighting its significant role in human iron physiology.