ERMAP is a single-pass type one membrane protein that belongs to the immunoglobulin superfamily. Expressed in cord blood, fetal liver and adult bone marrow, ERMAP is thought to function as a cell adhesion molecule in erythroid cells and is responsible for expression of the Scianna Radin (Sc Rd) blood group antigen system. The Sc Rd system is comprised of seven antigens that are present on the surface of red blood cells and have a variety of functions ranging from protein transport to cell adhesion. These seven blood antigens can differ in their expression within a population and may sometimes differ between mother and child. A fetus expressing different blood antigens than its mother may cause the mother to produce against the fetal blood. This condition is known as hemolytic disease of the newborn (HDN) and is characterized by jaundice, anemia and in some cases, infant death.