Hereditary spherocytosis

For patient information click here

Overview
Hereditary spherocytosis is a genetically-transmitted form of spherocytosis, an auto-hemolytic anemia characterized by the production of red blood cells that are sphere-shaped rather than donut-shaped, and therefore more prone to hemolysis.

Prevalence
It is the most common (1 in 5,000 of Northern European ancestry) disorder of the red cell membrane.

Pathophysiology
Hereditary spherocytosis is an autosomal dominant trait, most commonly (though not exclusively) found in Northern European and Japanese families, although an estimated 25% of cases are due to spontaneous mutations. A patient has a 50% chance of passing the disorder onto his/her offspring, presuming that his/her partner does not also carry the mutation.

Hereditary spherocytosis is caused by a variety of molecular defects in the genes that code for spectrin, ankyrin, protein 4.1, and other erythrocyte membrane proteins. These proteins are necessary to maintain the normal shape of an erythrocyte, which is a biconcave disk. The protein that is most commonly defective is ankyrin. As the spleen normally targets abnormally shaped red cells (which are typically older), it also destroys spherocytes.

Symptoms
As in non-hereditary spherocytosis, the spleen's hemolysis results in observational symptoms of fatigue, pallor, and jaundice.

Diagnosis
In a peripheral blood smear, the abnormally small red blood cells lacking the central pallor as seen in non-hereditary spherocytosis is typically more marked in hereditary spherocytosis.

Other protein deficiencies cause hereditary elliptocytosis, pyropoikilocytosis or stomatocytosis.

In longstanding cases and in patients who have taken iron supplementation or received numerous blood transfusions, iron overload may be a significant problem, being a potential cause of cardiomyopathy and liver disease. Measuring iron stores is therefore considered part of the diagnostic approach to hereditary spherocytosis.

Treatment
As in non-hereditary spherocytosis, acute symptoms of anemia and hyperbilirubinemia indicate treatment with blood transfusions or exchanges and chronic symptoms of anemia and splenomegaly indicate dietary supplementation of iron and splenectomy, the surgical removal of the spleen.

Experimental gene therapy exists to treat hereditary spherocytosis in lab mice; however, this treatment has not yet been tried on humans and because of the risks involved in human gene therapy, it may never be.