Illustration of an abnormal red blood cell (erythrocyte) known as stomatocyte. Red blood cells with this appearance occur in hereditary stomatocytosis. This disease arises from a dominant genetic defect in red blood cell membranes. The cells leak sodium and potassium ions, lose their normal indentation on one side forming a mouth-like shape (stoma), and eventually burst. This results in haemolytic anaemia and sometimes clotting problems. There is no specific treatment, but blood transfusions may sometimes be required.