A patient of 31 years of age with an atypical overhydrated hereditary stomatocytosis is described. The diagnosis was established on the basis of a markedly increased red cell volume with low MCHC, high osmotic fragility of red cells, but increased binding of eosin-5-maleimide (EMA) to red cells, presence of stomatospherocytes and large spherocytes in blood and a high sodium and low potassium concentration in erythrocytes. A double band 7 was found by SDS-PAGE of the erythrocyte membrane, but even when only one them was taken into account, the level of stomatin was normal. Expression of stomatospherocytes in patient's blood was erratic: in blood films prepared in 2005, both stomatospherocytes and large spherocytes were present but in those from 2008 large erythrocytes of spherocyte morphology predominated. Clinically, the disease symptoms were typical for haemolytic anemia. When heparinized blood of the patient was kept at 0 degrees Celsius for 24 h, the haemolysis of red cells amounted only to 2%. The patient's son, 5 years old, suffers from the same disease.
Conclusion: In spite of its rarity, hereditary stomatocytosis and allied disorders should be taken into consideration in differential diagnosis of haemolytic anemia including newborns. The diagnosis is supported by finding increased binding of eosin-5-maleimide (EMA) dye to patients' erythrocytes associated with their elevated osmotic fragility. Absence of a significant count of stomatocytes in the blood does not exclude the diagnosis of overyhydrated hereditary stomatocytosis.