|Classification and external resources|
Peripheral blood smear from patient with hereditary spherocytosis
Hereditary spherocytosis (also known as Minkowski–Chauffard syndrome) is a genetically-transmitted disorder. It exhibits incomplete penetrance in its expression. A form of spherocytosis, an auto-hemolytic anemia characterized by the production of red blood cells that are sphere-shaped rather than bi-concave disk shaped (donut-shaped), and therefore more prone to hemolysis.
It is the most common disorder of the red cell membrane, affecting 1 in 2,000 people of Northern European ancestry. According to Harrison's Principles of Internal Medicine, the frequency is at least 1 in 5,000.
Signs and Symptoms
As in non-hereditary spherocytosis, the spleen destroys the abnormal spherocytes. This hemolysis results directly in varying degrees of anemia (causing pallor and fatigue), hyperbilirubinemia (causing jaundice), and splenomegaly.
Acute cases can threaten to cause hypoxia through anemia and acute kernicterus through hyperbilirubinemia, particularly in newborns. Most cases can be detected soon after birth. An adult with this disease should have their children tested, although the presence of the disease in children is usually noticed soon after birth. Occasionally, the disease will not be noticed until the child is about 4 or 5 years of age.
Chronic symptoms include anemia, increased blood viscosity, and splenomegaly. Furthermore, the detritus of the broken-down blood cells—unconjugated or indirect bilirubin--accumulates in the gallbladder, and can cause pigmented gallstones or "sludge" to develop. In chronic patients, an infection or other illness can cause an increase in the destruction of red blood cells, resulting in the appearance of acute symptoms, a hemolytic crisis. Spherocytosis patients who are heterozygous for a hemochromatosis gene may suffer from iron overload despite the hemochromatosis genes being recessive 
In a peripheral blood smear, the red blood cells will appear abnormally small and lack the central pallor that is present in normal red blood cells. These changes are also seen in non-hereditary spherocytosis, but they are typically more marked in hereditary spherocytosis. The number of immature red blood cells (reticulocyte count) will be elevated.
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.
An osmotic fragility test can aid in the diagnosis. In this test, the spherocytes will rupture in mildly hypotonic solutions - this is due to increased permeability of the spherocyte membrane to salt and water. Although the osmotic fragility test is widely considered the gold standard for diagnosing hereditary spherocytosis, it misses as many as 25% of cases. Flow cytometric analysis of eosin-5′-maleimide-labeled intact red blood cells and the acidified glycerol lysis test are two additional options to aid diagnosis.
Hereditary spherocytosis is an autosomal dominant or recessive 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 mutation onto each of his/her offspring.
Hereditary spherocytosis is caused by a variety of molecular defects in the genes that code for spectrin (alpha and beta), ankyrin, band 3 protein, protein 4.2, and other erythrocyte membrane proteins:
These proteins are necessary to maintain the normal shape of an erythrocyte, which is a biconcave disk. The integrating protein that is most commonly defective is ankyrin which is responsible for incorporation and binding of spectrin, thus in its dysfunction cytoskeletal instabilities ensue.
The primary defect in hereditary spherocytosis is a deficiency of membrane surface area. Decreased surface area may be produced by two different mechanisms: 1) Defects of spectrin, ankyrin, or protein 4.2 lead to reduced density of the membrane skeleton, destabilizing the overlying lipid bilayer and releasing band 3-containing microvesicles. 2) Defects of band 3 lead to band 3 deficiency and loss of its lipid-stabilizing effect. This results in the loss of band 3-free microvesicles. Both pathways result in membrane loss, decreased surface area, and formation of spherocytes with decreased deformability.
As the spleen normally targets abnormally shaped red cells (which are typically older), it also destroys spherocytes. In the spleen, the passage from the cords of Billroth into the sinusoids may be seen as a bottleneck, where erythrocytes need to be flexible in order to pass through. In hereditary spherocytosis, erythrocytes fail to pass through and get phagocytosed, causing extravascular hemolysis.
- Hemolytic crisis, with more pronounced jaundice due to accelerated hemolysis (may be precipitated by infection).
- Aplastic crisis with dramatic fall in hemoglobin level and (reticulocyte count)-decompensation, usually due to maturation arrest and often associated with megaloblastic changes; may be precipitated by infection, such as influenza, notably with parvovirus B19.
- Folate deficiency caused by increased bone marrow requirement.
- Pigmented gallstones occur in approximately half of untreated patients. Increased hemolysis of red blood cells leads to increased bilirubin levels, because bilirubin is a breakdown product of heme. The high levels of bilirubin must be excreted into the bile by the liver, which may cause the formation of a pigmented gallstone, which is composed of calcium bilirubinate. Since these stones contain high levels of calcium carbonates and phosphate, they are radiopaque and are visible on x-ray.
- Leg ulcer.
- Abnormally low hemoglobin A1C levels. Hemoglobin A1C (glycated hemoglobin) is a test for determining the average blood glucose levels over an extended period of time, and is often used to evaluate glucose control in diabetics. The hemoglobin A1C levels are abnormally low because the life span of the red blood cells is decreased, providing less time for the non-enzymatic glycosylation of hemoglobin. Thus, even with high overall blood sugar, the A1C will be lower than expected.
At this point, there exists no cure for the genetic defect that causes hereditary spherocytosis. Current management focuses on interventions that limit the severity of the disease. Treatment options include:
- Splenectomy: 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 folic acid and splenectomy, the surgical removal of the spleen. Splenectomy is indicated for moderate to severe cases, but not mild cases. To decrease the risk of sepsis, post-splenectomy spherocytosis patients require immunization against the pneumococcus bacterium, influenza virus, and prophylactic antibiotic treatment. However, the use of prophylactic antibiotics, such as penicillin, remains controversial.
- Partial splenectomy: Since the spleen is important for protecting against encapsulated organisms, sepsis caused by encapsulated organisms is a possible complication of splenectomy. The option of partial splenectomy may be considered in the interest of preserving immune function. Research on outcomes is currently limited, but favorable.
- Cholecystectomy may be necessary.
Experimental gene therapy exists to treat hereditary spherocytosis in lab mice; however, this treatment has not yet been tried on humans due to all of the risks involved in human gene therapy.
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- An online HS resource from The University of Texas Southwestern Medical Center
- A short article from WebMD
- A picture of spherocytes from Medline