Overhydrated Hereditary Stomatocytosis

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.

Clinical description

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.

Etiology

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.

Diagnostic methods

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 (see these terms).

Genetic counseling

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

Management and 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.