Overhydrated hereditary stomatocytosis

Other Names: Potassium sodium disorder of erythrocyte; Stomatocytosis I

Overhydrated hereditary stomatocytosis (OHSt) is a disorder of red cell membrane permeability to monovalent cations and is characterized clinically by hemolytic anemia.

Epidemiology

OHSt is very rare with only seven cases described in the literature so far.

Cause

In the majority of cases, OHSt is caused by mutations in the RHAG gene (6p21-qter) encoding the Rh-associated glycoprotein component of the Rh complex.

Inheritance

Autosomal dominant pattern, a 50/50 chance.

OHSt is transmitted as an autosomal dominant trait but de novo mutations are quite common.

Signs and symptoms

Onset occurs during the neonatal period or infancy with hemolytic anemia that may require occasional blood transfusions. Splenomegaly or hepatosplenomegaly are present. The disease course is marked by the usual complications of hemolytic anemia (biliary lithiasis) and, remarkably, by a strong tendency for iron overload.

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. 80%-99% of people have these symptoms

• Abnormal mean corpuscular volume
• Decreased mean corpuscular hemoglobin concentration
• Hemolytic anemia
• Increased red cell osmotic fragility
• Reticulocytosis(Increased immature red blood cells)
• Stomatocytosis

5%-29% of people have these symptoms

• Abnormal thrombosis(Abnormal blood clot)
• Anisocytosis(Unequal size of red blood cells)
• Increased lactate dehydrogenaselevel
• Intermittent jaundice(Intermittent yellow skin)
• Splenomegaly(Increased spleen size)

Diagnosis

Diagnosis is based on a massive right shift of the osmotic gradient ektacytometry curve indicating overhydrated red cells and decreased osmotic resistance, together with a substantial increase in the monovalent cation leak compared to controls, and a sharp decrease of the leak as a function of decreasing temperature. Blood smears show an elevated percentage of well formed stomatocytes. There is macrocytosis, a low mean cell hemoglobin concentration (MCHC) and a high reticulocyte count. Electrophoresis reveals that the membrane protein stomatin is absent or present at only low levels.

Differential diagnosis The differential diagnosis should include the most common form of hereditary stomatocytosis, dehydrated hereditary stomatocytosis, as well as hereditary cryohydrocytosis with reduced stomatin.

Treatment

Treatment involves blood transfusions, when necessary, together with management of biliary lithiasis and iron overload. Splenectomy is contraindicated in OHSt patients as it may induce venous thromboembolic complications.

Prognosis

With correct management of the complications, the prognosis is good.

NIH genetic and rare disease info

• NIH info on Overhydrated hereditary stomatocytosis

Overhydrated hereditary stomatocytosis is a rare disease.

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