An inherited, mild, non-hemolytic subtype of hereditary stomatocytosis that is associated with a temperature-dependent anomaly in red cell membrane permeability to potassium that leads to high in vitro potassium levels in samples stored below 37°C. Not associated with additional hematological abnormalities, although affected individuals may show some mild abnormalities like macrocytosis. All families identified so far have mutations in the ABCB6 gene (2q36), leading to an inherited abnormality in the movement of ions across the red cell membrane, such that when the red cells are cooled they lose potassium into the plasma. Inherited as an autosomal dominant trait. The prognosis is excellent most patients remain asymptomatic.