Protein 4.1 (80 kD) interacts with spectrin and short actin filaments to form the erythrocyte membrane skeleton.

Mutations of spectrin and protein 4.1 are associated with elliptocytosis or spherocytosis and anemia of varying severity.

Elliptocytosis is a hematologic disorder characterized by elliptically shaped erythrocytes and a variable degree of hemolytic anemia.

Inherited as an autosomal dominant, elliptocytosis results from mutation in any one of several genes encoding proteins of the red cell membrane skeleton.

The form discussed here is the one found in the 1950s to be linked to Rh blood group and more recently shown to be caused by a defect in protein 4.1.