Osmosis leads to the red blood cell having a constant tendency to swell and burst. This tendency is countered by manipulating the flow of sodium and potassium ions. A 'pump' forces sodium out of the cell and potassium in, and this action is balanced by a process called 'the passive leak'. In the<unk> , the passive leak is increased and the cell becomes swamped with salt and water. The cell lyses and a haemolytic anaemia results. For as yet unknown reasons, the cells take on the shape of a cup, with a 'mouth-shaped' (stoma) area of central pallor. The two varieties of<unk>  classified with respect to hydration status are overhydrated (hydrocytosis) and dehydrated (xerocytosis).
Hereditary stomatocytosis
Hereditary sclerosing poikiloderma
Hypohidrotic ectodermal dysplasia
Hereditary angioedema
Nickel allergy
Rapunzel syndrome
Hereditary mucoepithelial dysplasia
Griscelli syndrome