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Hereditary Spherocytosis (HS)
Sunday, 27 July 2003
Monday, 29 November 2004

What

Hereditary spherocytosis (HS) is caused by a genetic defect that produces abnormally shaped red blood cells (RBC). The defect causes a change in the protein composition of the cell membrane thereby affecting the surface area of the cell and giving it the characteristic abnormal spherical shape. These cells are less deformable than normal RBCs and are prone to premature destruction and removal by the spleen leading to hemolytic anemia. A hemolytic anemia is characterized by the breaking down of RBCs with the liberation of hemoglobin, which diffuses into the surrounding fluid. Because spherocytic red blood cells are less flexible than normal cells and rupture more easily they are said to be “osmotically fragile.” Persons with this disorder usually present with the triad of jaundice (yellow skin pigmentation), anemia and enlarged spleen. Some children may also complain of fatigue, weakness and shortness of breath, primarily due to the anemia.

Who

Hereditary spherocytosis occurs predominantly in people of northern European descent. It has also been observed in the Japanese and southern African black populations, although with a much lower incidence. Males and females are affected with equal frequency. The condition may be present within a day or two of birth, while in other cases it is detected only by chance and much later in life. In at least 75% of cases, the disease results from the inheritance of a single affected gene, from either parent. The parent with this affected gene would also have this condition and the mode of inheritance is said to be “dominant.” However, in the remaining 25% of families, both parents are normal. This suggests that in these cases the mode of inheritance may be “recessive,” meaning that each parent carries one good copy and one bad copy of the gene and it is only when both bad copies are inherited together that the condition is manifested. It is also possible that a new mutation, or permanent change in the genetic make-up of an individual, occurred spontaneously for unknown reasons.

Signs and Symptoms

The majority (approximately 2/3) of individuals with HS has jaundice, anemia and an enlarged spleen. These symptomatic individuals may also have an uncompensated hemolytic anemia, meaning that their body is not able to replace the lost red blood cells fast enough. A minority of individuals (10%) has a severe hemolytic anemia that may require a blood transfusion. Some patients may develop gallstones. Some people, however, do not show any symptoms at all. These individuals have a mild hemolytic anemia that is compensated for; therefore, they are not anemic and have no other major symptoms.

Possible Causes

The exact mechanism of spherocyte formation is not completely understood, but HS is known to be caused by a genetic defect. Hereditary spherocytosis results from a deficiency of spectrin or other structural proteins of the RBC membrane skeleton. This weakens the cell membrane, changing the cell shape from a disc to a sphere.

Diagnosis

To confirm a case of hereditary spherocytosis, a variety of laboratory tests on the patient’s blood sample is conducted. A peripheral blood smear, which yields a picture of the red blood cells, reveals their abnormal spherical shape. By-products of RBC breakdown are also found in the blood, providing evidence for their premature destruction. A series of additional exams, termed “red cell indices” help to confirm cases of anemia. The tendency of these red blood cells to rupture can be sensed by special osmotic fragility tests. Additional tests exist that confirm the protein composition of the RBC membrane and its structural and metabolic integrity.

Treatment

In the majority of patients with this disease, the treatment for anemia is the surgical removal of the spleen, called a “splenectomy.” This results in RBCs with a normal or very near normal life span, although they are still shaped as spherocytes. While splenectomy is curative it is not without risks. The spleen plays a major role in the immune defenses of the body. Bacteria carried by the blood pass through the spleen and become trapped by special immune cells. Thus, because the spleen is actively involved in developing a child’s immune system most authorities recommend that it not be performed until the child reaches 5 years of age.

Prognosis

Hereditary spherocytosis has an excellent prognosis. The classic symptoms are effectively eliminated after splenectomy, in all but the most severe cases, and life expectancy is normal. Serious infection occurring after splenectomy can be minimized by undergoing vaccination against pneumococcus and meningiococcus bacteria prior to the splenectomy, in addition to normal childhood vaccines. Another long-term safety precaution in the child’s best interest may be to wear a Medic Alert bracelet.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.

Weblinks

Medline Plus
This is a concise, well-written overview of HS with nice pictures of peripheral smears.

CCHS Digital Library
A great website with links to many informational and supportive sites specifically about HS. There are sites in English and in Spanish.

Google Search for Hereditary Spherocytosis (HS)

References and Sources

www.nlm.nih.gov/medlineplus/ency/article/000530.htm hsc.virginia.edu/medicine/clinical/pathology/educ/innes/text/rcd/membrane.html www.intelihealth.com/IH/ihtIH?d=dmtContent&c=237963&p=~br,IHW|~st,408|~r,WSIHW000|~b,*| www.merck.com/mrkshared/mmanual_home/sec14/154.jsp