Hereditary Stomatocytosis comprises two different diseases: the xerocytosis or dehydrated hereditary stomatocytosis and the overhydrated hereditary stomatocytosis. Both are genetic disorders mainly due to abnormality of red cell membrane permeability to monovalent cations (Na+ and K+) resulting in an alteration in the red blood cell water content. Typical red blood cells known as stomatocytes (mouth featured cells) appear in blood smear examination. The clinical manifestation can vary from asymptomatic to severe haemolytic anaemia.
Hereditary xerocytosis is a genetic disease characterised by red cell dehydration, due to the loss of the cation content, in particular K+ and cell water. Strikingly, the red cell survival is not significantly decreased. The clinical manifestation varies from mild to moderate anaemia. Mutations in the ionic channel PIEZO1 gene have been described as causative of this disease in unrelated families. Overhydrated hereditary stomatocytosis is a genetic disease characterised by red cell overhidratation due to an excess of cations resulting in an increased water content and volume. As a consequence, a high number of large and fragile stomatocytes are present in this disease leading to a moderate to severe form of haemolytic anaemia. Mutations in Rhassociated glycoprotein (RhAG) have been reported. Hereditary xerocytosis has an estimated prevalence of 1 patient out of 50.000 individuals; meanwhile only less than 10 patients are estimated to be affected by overhydrated stomatocytosis per 1.000.000 individuals. However, this prevalences could be higher since hereditary stomatocytosis is easily misdiagnosed as hereditary spherocytosis. Other rarer and heterogeneous forms of hereditary stomatocytosis (i.e. cryohydrocytosis, familial pseudohyperkalemia) have been described, some of them due to mutations in the transmembrane domain of band3 (SLC4A1 gene) and in glucose transporter 1 (SLC2A1 gene) or ABCB6 gene. Rare cases of cryohydrocytosis may present neurological abnormalities.
Hereditary xerocytosis is characterised by well-compensated mild to moderate anaemia. Complications such as splenomegaly and cholelithiasis, resulting from increased red cell trapping in the spleen and elevated bilirubin levels, respectively, may occur. The course of hereditary xerocytosis is frequently associated with iron overload, and not with severe anaemia. Even though overhydrated hereditary stomatocytosis has a much lower prevalence than hereditary xerocytosis the clinical burden is higher as this disease leads to a more severe form of haemolytic anaemia.
The treatment of haemolytic anaemia is based on supportive measures: folate therapy is recommended in mild to severe forms, and red cell transfusions may be required in severe cases. Chelating therapy may be required to reduce iron overload due to periodical red cell transfusions. Since iron overload is more likely in this disease than in other haemolytic anaemias, periodic iron overload quantification and iron chelation therapy is highly recommended. Regular follow-up for monitoring gallstones should always be considered. Splenectomy is completely contraindicated in both types of hereditary stomatocytosis because of an increased risk of thromboembolic complications.
The inheritance of hereditary stomatocytosis is autosomal dominant. Autosomal dominat pattern: Only one copy of a mutated gene, from the mother or from the father, is needed to develop the disease. In these cases, the mother or the father is affected by the disease having one mutated gene. The couple has a 50 percent probability of having a child affected by the disease at each pregnancy. The probability of having a healthy child with no mutated gene is also 50 percent at each pregnancy. Ask for genetic counselling to get a complete explanation.