<unk>  is a disorder of the surface layer (membrane) of red blood cells. It leads to red blood cells that are shaped like spheres, and premature breakdown of red blood cells (hemolytic anemia).
Hereditary spherocytosis
Paroxysmal nocturnal hemoglobinuria
Paroxysmal cold hemoglobinuria
Familial erythrocytosis
Hereditary elliptocytosis
Congenital hemolytic anemia
Sideroblastic anemia
Beta-thalassemia