HERDITARY SPHEROCYTOSIS is a familial hemolytic disorder

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Hemolytic anemiaanemia is a condition in which there are not enough red blood cells in the blood, due to the premature destruction of red blood cells. There are a number of specific types of hemolytic anemia; one of them is hereditary spherocytosis (HS). HS is a familial hemolytic disorder with marked heterogeneity of clinical features, ranging from an asymptomatic condition to fulminate hemolytic anemia. HS is an inherited disease that causes anemia. If the child has HS, either parent may also have the disease. Occasionally, neither parent of an affected child has the disease; this is considered a spontaneous mutation.(1) HS is inherited as a dominant trait so, if a person with HS reproduces, their child (irrespective of whether it is a boy or girl) has a 50:50 chance to have HS. (2)

Hereditary spherocytosis (HS) was described in 1871 and the first recorded splenectomy was performed soon after. It is the commonest cause of inherited chronic hemolysis in Northern Europe and North America with a quoted incidence of 1 in 5000 births. HS has also been found in other ethnic groups (in Africa, Algeria, Tunisia, Egypt, Japan, North India and Brazil). There are only rare cases reported in the black population. In the last 15 years significant progress has been made in the understanding of the biochemical and molecular genetic basis of HS. (1)


Hereditary spherocytosis is a congenital hemolytic anemia due to defect in RBC membrane protein known as spectrin, and is transmitted as autosomal dominant. Due to this defect there is presence of characteristic spherical cell in peripheral blood smear, osmotic fragility is increased, hemolytic anemia, reticulocytosis, jaundice and splenomegaly. (3)

The osmotic fragility test is done to confirm the diagnosis of hereditary spherocytosis. Patient's red blood cells are placed in different concentrations of saline solution for 24 hours. When red blood cells are placed in saline solution, they absorb water until the cell membrane bursts. Spherocytes do not tolerate weak saline solutions, causing them to burst sooner than normal cells. (4)

The congestion of the spleen with red cells causes splenomegaly. The destruction of the red cells releases hemoglobin and the heme part gives rise to bilirubin. The hyper bilirubinemia is the cause of jaundice, and the formation of gallstones, even in childhood. There is also often iron overload due to the excess destruction of iron-rich red cells. (5)


The RBC membrane disorders are uncommon in the Middle East. The major inherited RBC membrane abnormalities worldwide are hereditary spherocytosis. (6) In HS the red cells are smaller, rounder, and more fragile than normal. The red cells have a spherical rather than the biconcave-disk shape of the normal red cell. These round red cells (spherocytes) are osmotically fragile and less flexible than normal red cells and tend to get trapped in narrow blood passages, particularly in the spleen, and there they break up (hemolyze) leading to hemolytic anemia. (5)

The bone marrow has to work extra hard to make more red cells. So, if in the course of an ordinary viral illness, the bone marrow stops making red cells, the anemia can quickly become profound. This is termed an aplastic crisis. (3)

RBCs circulate in the blood and contain hemoglobin, which carries oxygen to all parts of the body. Normal RBCs are shaped like a disc. Alterations in membrane proteins cause the RBC abnormalities. In HS, the cell membrane surface area is decreased disproportionately to the intracellular content. The decreased surface area of the cell impairs the flexibility needed for the cell to traverse the spleen's microcirculation, causing intrasplenic hemolysis. Also spherocytes are round and fragile and does not change shape to pass through certain organs as easily as normal RBCs. Because spherocytes cannot change their shape easily, they stay in the spleen longer than normal red blood cells, and the membrane surrounding the cell becomes damaged. After circulating through the spleen many times, the cell eventually becomes so damaged that it is destroyed by the spleen. (5)

This disorder is caused by a defective gene. This defect results in an abnormal red blood cell membrane. The affected cells have a smaller surface area for their volume than normal red blood cells, (7)


Symptoms of hereditary spherocytosis vary depending on the severity of the disease. Many people with hereditary spherocytosis have a normal hemoglobin level. Most patients have only a mild anemia. These patients compensate by making more red blood cells, which is measured by the reticulocyte (immature red blood cell) count. However, infection, fever and stress can stimulate the spleen to destroy more red blood cells than usual. If this occurs, the child's hemoglobin level will drop and the bilirubin level increase, causing yellowish coloration of the skin and the eyes.


Other symptoms may include:



Shortness of breathShortness of breath

WeaknessWeakness (7)

Examination and Tests:

Exams and Tests

In most cases, the spleen is enlarged. Laboratory tests can help diagnose this condition, tests may include:

Blood smear to show abnormally shaped cells (spherocytes)

Bilirubin level is elevated

Complete blood count to detect anemia and increased Mean Corpuscular Hemoglobin Concentration. Because RBCs are spheroidal and the MCV is normal, the mean corpuscular diameter is below normal, and RBCs resemble microspherocytes. MCHC is increased.

Reticulocyte countReticulocyte count is increased (15%-30%). (7)

Coombs' testCoombs' test is negative. It is positive in spherocytosis with immune hemolytic anemia

LDH level is elevated due to RBCs destruction

Osmotic fragilityOsmotic fragility of RBCs is increased. Hemolysis of HS cells may be complete at a solute concentration that causes little or no lysis of normal cells. Not uncommonly, some individuals with HS have a normal fresh osmotic fragility test result. Osmotic fragility after prolonged incubation at 37°C usually is abnormal.

Acidified glycerol lysis test (AGLT)

Osmotic gradient ektacytometry: A laser diffraction viscometer that measures red cell deformability at constant shear stress as a continuous function of suspending osmolality (hypotonic to hypertonic)

Flow cytometry: The eosin-5-maleimide (EMA) binds to band 3, a skeletal protein, and the test has a high sensitivity (92.7%) and specificity (99.1%) for HS. The test can be performed rapidly (within two hours) on a small sample of blood. (8,9)


Hemolysis in HS results from the interplay of an intact spleen and an intrinsic membrane protein defect that leads to abnormal RBC morphology. HS erythrocytes are caused by membrane protein defects resulting in cytoskeleton instability. Spectrin deficiency leads to loss of erythrocyte surface area, which produces spherical RBC's. Spherocytic RBC's are collected rapidly from the circulation by the spleen. Patients with HS develop splenomegaly. Biochemical spectrin deficiency and the degree of spectrin deficiency are reported to correlate with the extent of spherocytosis, and the severity of hemolysis. Hemolysis primarily occurring in the spleen and, therefore, is extravascular. Spectrin deficiency is the result of impaired synthesis, whereas in other instances, it is caused by quantitative or qualitative deficiencies of other proteins that integrate spectrin into the cell membrane. In the absence of these binding proteins, free spectrin is degraded, leading to spectrin deficiency.

Four abnormalities in red cell membrane proteins have been identified and include:

(1) Spectrin deficiency alone

(2) Combined spectrin and ankyrin deficiency

(3) Band 3 deficiency

(4) Protein 4.2 defects

Spectrin deficiency is the most common defect. Each is associated with a variety of mutations that result in different protein abnormalities and varied clinical expression. Most cases of HS are heterozygous because homozygous states are lethal. (10)

(Fig.1) Schematic presentation of the structural organization of red cell cytoskeleton. (11)

HS red cells are found to have single or combined protein deficiencies as determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) (table 1, 2) (1)

(Table 1) Probable primary causes for producing the observed (or secondary) membrane protein defects.

Observed protein deficiency by SDS-PAGE

Primary defect in protein or gene

Partial spectrin and protein 4·2 deficiency

Missing one haploid set of ANK1

Partial ankyrin and spectrin deficiency

Ankyrin gene mutation(s)

Partial spectrin deficiency

A variety of molecular defects

Marked deficiency of spectrin (parents are normal)

Severe ndHS due to low expression allele inherited in trans to a second Sp allele (i.e. HS)

Partial band 3 deficiency

Band 3 mRNA instability

Partial protein 4·2 deficiency

Band 3 gene mutations resulting in loss of protein 4·2 binding site

(Table 2) Membrane molecules associated with erythrocyte cytoskeleton.


Band on gel

Mr (kD)


Chromosomal location

Number of exons

α Spectrin






β Spectrin












Band 3 (AE1)



AE1 (SLC4A1)



Protein 4·1






Protein 4·2






Glycophorin C






Genetic aspect: (12, 13, 14)

Spectrin deficiency:

Mutations of alpha-spectrin are associated with recessive forms of HS, whereas mutations of beta-spectrin occur in families with autosomal dominant forms of HS. Synthesis of alpha-spectrin is 3-fold greater than that of beta-spectrin. The excess alpha chains normally are degraded. Heterozygotes for alpha-spectrin defects produce sufficient normal alpha-spectrin to balance normal beta-spectrin production. Defects of beta-spectrin are more likely to be expressed in the heterozygous state because synthesis of beta-spectrin is the rate-limiting factor. Red cell membranes isolated from individuals with autosomal recessive HS have only 40-50% of the normal amount of spectrin (relative to band protein 3), whereas red cell spectrin levels range from 60-80% of normal in the autosomal dominant form of HS.

Identification of an alpha-spectrin mutation involves a point mutation at codon (969), resulting in an amino acid substitution {alanine (Ala)/ aspartic acid (Asp)} at the corresponding site of alpha-spectrin in 50% of patients with severe recessive HS. Mutations involving the alpha-spectrin beta-spectrin gene also occur, each resulting in spectrin deficiency. The first identified point mutation leads to a defective binding of spectrin to protein 4.1. Several other beta-spectrin mutations have been identified. Some of these mutations result in impaired beta-spectrin synthesis. Others produce unstable beta-spectrins or abnormal beta-spectrins that do not bind to ankyrin and undergo proteolytic degradation.

Ankyrin defects:

HS is due to a deficiency of a protein called ankyrin. Ankyrins are cell membrane proteins that interconnect integral proteins with the spectrin-based membrane skeleton. The ankyrin of red blood cells (erythrocytic ankyrin) is called ankyrin-R or ankyrin-1. It is represented by the symbol ANK1. The gene of ANK1, has been mapped to chromosome 8 and, specifically, to chromosome band 8p11.2.

HS is described in patients with translocation of chromosome 8 or deletion of the short arm of chromosome 8 where the ankyrin gene is located, and patients with HS and deletion of chromosome 8 are shown to have a decrease in red cell ankyrin content. Ankyrin is the principal binding site for spectrin on the red cell membrane. In HS caused by ankyrin deficiency, a proportional decrease in spectrin content occurs, although spectrin synthesis is normal. Of particular interest, 75-80% of patients with autosomal dominant HS have combined spectrin and ankyrin deficiency and the 2 proteins are diminished equally.

Band 3 deficiency:

Band 3 deficiency has been recognized in 10-20% of patients with mild-to-moderate autosomal dominant HS. These patients also have a proportionate decrease in protein 4.2 content on the membrane. In some people with HS who are deficient in band 3, the deficiency is considerably greater in older RBCs. This suggests that band 3 protein is unstable.

Protein 4.2 (pallidin) deficiency:

Deficiency of protein 4.2 in HS is relatively common in Japan. One that appears to be common in the Japanese population (protein 4.2 Nippon). Another mutant protein 4.2 (protein 4.2 Lisboa) is caused by a deletion that results in a complete absence of protein 4.2. This is associated with a typical HS phenotype.

HS usually is transmitted as an autosomal dominant trait, and the identification of the disorder in multiple generations of affected families is the rule. Homozygosity for this dominantly transmitted HS gene has not been identified. 25% percent of all newly diagnosed patients do not demonstrate a dominant inheritance pattern. Parents of these patients do not have clinical or hematological abnormalities. New mutations have been implicated that may explain some of these sporadic cases.

An autosomal recessive mode of inheritance also occurs. This is supported by the descriptions of families in which apparently healthy parents have had more than one affected child. This recessive pattern may account for 20-25% of all HS cases. It manifests only in individuals who are homozygous or compound heterozygous and often is associated with severe hemolytic anemia.

The RBC membrane disorders are uncommon in the Middle East. The major inherited RBC membrane abnormalities worldwide are hereditary spherocytosis and hereditary elliptocytosis. Quite rare are hereditary pyropoikilocytosis. These conditions may be associated with chronic hemolytic anemia of varying severity, depending on the specific genetic mutation.(6) Hereditary spherocytosis is most common in Northern Europeans, but it also occurs in North Africa. In Egypt, a study on RBCs membrane of HS children using 10% gel and a discontinuous buffer system. Gels were stained with Coomassie blue and bands were identified and quantitated by scanning, a combined spectrin/ankyrin defect was the most frequently occurring abnormality (85%), next was an isolated ankyrin defect (10%), with an isolated alpha spectrin defect as the least frequently occurring abnormality (5%).(15)

Possible Complications:

Possible Complications

GallstonesGallstones : Bilirubin gallstones are found in approximately 50% of patients with HS and frequently are present in patients with very mild disease.(1)

Aplastic anemia: Much lower red blood cell production (aplastic crisis) caused by a viral infection, which can make anemia worse.(7)

Rare complications: Growth failure may occur in severe cases, with marrow expansion and skeletal deformities. Leg ulcers have been described. Several unsplenectomized adult patients have been reported with extramedullary haemopoiesis, occasionally as the presenting feature of the disease.( 1)


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. 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. Children with spherocytosis require immunization against the pneumococcus bacterium and prophylactic antibiotic treatment as well to decrease the risk of sepsis. (5)


After splenectomy, RBC survival improves dramatically, enabling most patients with HS to maintain a normal hemoglobin level. (7)