Protein 4.1R, the first identified member of the family, is a key protein in red blood cells, where it anchors the actin-spectrin cytoskeleton to glycophorin C. This anchoring is critical for the biconcave shape of red blood cells since mutations in either protein 4.1R or glycophorin C result in hereditary elliptocytosis and hemolytic anemia. This evidence concerns the gene GYPC and hereditary elliptocytosis.