Hereditary Stomatocytosis

At a glance

Series of inherited forms of hemolytic anemia caused by alterations in the red cell membrane, resulting in leakage of sodium and potassium. After resaturation of normal permeability, red cell membrane rigidity, morphology, water content, and cell cation return to normal. Low potassium is dominant to high potassium.

Synonyms

Cryohydrocytosis; Overhydrated Hereditary Stomatocytosis.

Incidence

Unknown. Approximately 1:10,000 kindreds in France and the United Kingdom have hereditary xerocytosis. Familial pseudohyperkalemia does not seem to occur in the United States.

FYI: Stomatocytosis is also found as a hereditary disease in Alaskan malamute and miniature schnauzer dogs.

Classification

A number of variants have been described. They include:

• Overhydrated Hereditary Stomatocytosis

• Dehydrated HSt (Hereditary Xerocytosis; Hereditary Hyperphosphatidylcholine Hemolytic Anemia)

• Dehydrated with Perinatal Ascites

• Cryohydrocytosis

• “Blackburn” Variant Syndrome

• Familial Pseudohyperkalemia

Genetic inheritance

Autosomal dominant. Mutation located on chromosome 16, but the gene is not yet identified. Except for hereditary xerocytosis, the red blood cell membrane of stomatocytoses is defective for the stomatin protein (or “erythrocyte membrane protein 7.2b”).

Pathophysiology

The red blood cells have a membrane abnormality with increased permeability to cations, with a greater efflux of potassium than sodium. Consequently, these red cells lose potassium in excess of the sodium gained, with a decrease in total cation content.

Diagnosis

Laboratory findings include hemoglobinuria, reticulocytosis, increased red cell hemolysis by shear stress, increased mean corpuscular volume, and increased mean corpuscular hemoglobin concentration. The visual aspect of red blood cells varies depending on the variant: very stomatocytic for the rather common overhydrated hereditary stomatocytosis, xerocytic for the rarer dehydrated hereditary stomatocytosis, and no anemia in familial pseudohyperkalemia.

Clinical aspects

Patients generally have few symptoms but may have exercise-induced episodes of fatigue, associated with jaundice, pallor, or darkened urine. Splenomegaly and cholelithiasis may occur. Hemoglobin levels are often normal or near-normal, despite clinical and laboratory evidence of mild-to-moderate hemolysis (except for familial pseudohyperkalemia). Blood transfusions are generally not required, and the benefit of splenectomy is slight. Furthermore, if the spleen is removed, problems with excessive blood clotting may arise later in life. Iron overload may develop later in life.

Precautions before anesthesia

Check hemoglobin level and reticulocyte count. The leakage of potassium might be important and preoperative electrolytes measurement must be obtained.

Anesthetic considerations

Potential reduction in oxygen delivery because of decreased levels of 2,3-diphosphoglycerate. Make sure that potassium level is within normal limits.

Pharmacological implications

No known specific implications for this condition.

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