General considerations of hemolytic diseases, red cell membrane, and enzyme defects

Genetics

• Autosomal dominant inheritance (75% of cases). The severity of anemia and the degree of spherocytosis may not be uniform within an affected family

• No family history in 25% of cases. Some show minor laboratory abnormalities suggesting a carrier (recessive) state. Others are due to a de novo mutation

• Most common in people of northern European heritage, with an incidence of 1 in 5000.

Pathogenesis

The primary defect is membrane instability due to dysfunction or deficiency of a red cell skeletal or membrane protein, including:

• Ankyrin mutations account for 50–60% of HS. In many patients, both spectrin and ankyrin proteins are deficient. Mutations of ankyrin occur in both dominant and recessive forms of HS. The clinical course varies from mild to severe. Red cells are typically spherocytes

• α-Spectrin mutations occur in recessive HS and account for less than 5% of HS. The clinical course is severe. Contracted cells, poikilocytes, and spherocytes are seen

• β-Spectrin mutations occur in dominant HS and account for 15–20% of HS. The clinical course is mild to moderate. Acanthocytes, spherocytic elliptocytes, and spherocytes are seen

• Protein 4.2 mutations occur in the recessive form of HS and account for less than 5% of HS. The clinical course is mild to moderate. Spherocytes, acanthocytes, and ovalocytes are seen

• Band 3 mutations occur in the dominant form of HS and account for 15–20% of HS. The clinical course is mild to moderate. Spherocytes are occasionally mushroom-shaped or pincered cells. The deficiency of these proteins in HS results in a vertical defect, which causes progressive loss of membrane lipid and surface area. The loss of surface area results in characteristic microspherocytic morphology of HS red cells. The sequelae are as follows:

• Depletion of membrane lipid

• Decrease in membrane surface area relative to volume, resulting in a decrease in surface-area-to-volume ratio

• Tendency to spherocytosis

• Influx and efflux of sodium increased; cell dehydration

• Sequestration of red cells in the spleen due to reduced erythrocyte deformability

• Rapid ATP utilization and increased glycolysis leading to increased loss of surface area under ATP-depleted conditions. This leads to the observation of splenic conditioning where the changes in glucose utilization, as well as cell volume control, are dramatically exacerbated with each circulatory passage through the spleen.

• Premature red cell destruction.

Hematologic features

• 1.

  Anemia : mild to moderate when there is a compensated hemolytic anemia. In erythroblastopenic (aplastic or hypoplastic) crisis, hemoglobin may drop to 2–3 g/dL

• 2.

  MCV usually decreased, mean corpuscular hemoglobin concentration (MCHC) raised, and RDW elevated.

  • a.

    The MCHC is raised in HS, hereditary xerocytosis, hereditary pyropoikilocytosis (HPP), pyruvate kinase (PK) deficiency (which has acquired xerocytosis), and cold agglutinin disease. The presence of elevated RDW and MCHC (performed by aperture impedance instruments, e.g., Coulter) makes the likelihood of HS very high, because these two tests used together are very specific for HS

• 3.

  Reticulocytosis (3–15%)

• 4.

  Blood smear : spherocytes, microspherocytes (vary in number); hyperdense cells with or without polychromasia. The percentage of microspherocytes is the best indicator of the severity of the disease but not a good discriminator of the HS genotype. Hyperdense cells are seen in HbSC disease, HbCC disease, and xerocytosis. In HS, hyperdense cells are a poor indicator of disease severity but an effective discriminating feature of the HS phenotype

• 5.

  Direct antiglobulin test (DAT) negative

• 6.

  Increased red cell osmotic fragility (spherocytes lyse in higher concentrations of saline than normal red cells) occasionally only demonstrated after incubation of blood sample at 37°C for 24 h (therefore always do this test incubated). In spite of normal osmotic fragility, increased MCHC or an increase in hyperdense red cells is highly suggestive of HS

• 7.

  Autohemolysis at 24 and 48 h increased, corrected by the addition of glucose

• 8.

  Survival of ⁵¹ Cr-labeled cells reduced with increased splenic sequestration

• 9.

  Marrow: normoblastic hyperplasia; increased iron

• 10.

  Eosin-5-maleimide dye staining of red cells and analysis by flow cytometry is the test of choice to diagnose HS but is only available in special reference laboratories

• 11.

  Genetic analysis for the α- and β-spectrin, ankyrin, and band 3 mutations is available, but rarely necessary to be performed for diagnosis.

Biochemical features

• 1.

  Indirect hyperbilirubinemia

• 2.

  Obstructive jaundice with increased direct bilirubin; may develop due to gallstones, a consequence of increased pigment excretion.

Clinical features

• 1.

  Anemia and jaundice: severity depends on rate of hemolysis, degree of compensation of anemia by reticulocytosis, and ability of liver to conjugate and excrete indirect hyperbilirubinemia

• 2.

  Splenomegaly

• 3.

  Presents in newborn period in 50% of cases with hyperbilirubinemia, reticulocytosis, normoblastosis, spherocytosis, negative DAT, and splenomegaly. Patients may present with a requirement for transfusion in the first 8 weeks of life that may not be reflective of their ultimate clinical severity

• 4.

  Presents before puberty in most patients

• 5.

  Diagnosis sometimes made much later in life, often after the birth of an infant with neonatal jaundice caused by HS

• 6.

  Coinheritance of HS with HbSC disease may increase the risk of splenic sequestration crisis

• 7.

  Coinheritance of α- or β-thalassemia trait and HS has been reported to have variable effects on hemolysis

• 8.

  Iron deficiency may correct the laboratory values (artificially reducing the MCHC, etc.) but not the red cell life span in HS patients

• 9.

  HS with other system involvement:

  • a.

    interstitial deletion of chromosome 8p11.1–8p21.1 causes ankyrin deficiency, psychomotor retardation, and hypogonadism,

  • b.

    HS may be associated with neurologic abnormalities such as cerebellar disturbances, muscle atrophy, and a tabes-like syndrome,

  • c.

    in patients presenting with common bile duct obstruction associated with gallstones, the increased cholesterol and triglyceride load from the induced dyslipidemia can correct the membrane defect and the resulting spherocyte morphology, MCHC, and osmotic fragility results, hence masking the diagnostic features of the disease. The removal of bile duct obstruction leads to a reappearance of the disease phenotype.

Classification

Table 7.1 lists a classification of HS in accordance with clinical severity and indications for splenectomy.

Diagnosis

• Clinical features and family history

• Hematologic features.

Complications

• 1.

  Hemolytic crisis : with more pronounced jaundice due to accelerated hemolysis (may be precipitated by viral infection)

• 2.

  Erythroblastopenic crisis ( hypoplastic crisis ): dramatic fall in hemoglobin level (and reticulocyte count); usually due to maturation arrest and often associated with giant pronormoblasts in the recovery phase; often associated with parvovirus B19 infection. Parvovirus B19 infects developing normoblasts, causing a transient cessation of production. The virus specifically infects Colony-Forming Unit-Erythroid and prevents their maturation. Giant pronormoblasts are seen in bone marrow. Diagnosis is made by increased IgM antibody titer against parvovirus and polymerase chain reaction for parvovirus on bone marrow

• 3.

  Folate deficiency : caused by increased red cell turnover; may lead to superimposed megaloblastic anemia. Megaloblastic anemia may mask HS morphology as well as its diagnosis by osmotic fragility

• 4.

  Gallstones (in approximately one-half of untreated patients): increased incidence with age, can occur as early as 4–5 years of age. Occasionally, HS may be masked or improved in obstructive jaundice due to increase in surface area of red cells and the coinheritance of Gilbert syndrome markedly increases the incidence of gallstones

• 5.

  Complications of chronic anemia : patients with more severe HS (see Table 7.1 ) may suffer growth retardation, anemic heart failure, and failure to thrive, necessitating intermittent or chronic transfusion

• 6.

  Hemochromatosis: rarely, this may occur more frequently when a restricted or partial splenectomy is carried out (see next)

• 7.

  Splenic rupture: the risk of splenic rupture in HS is similar to that of the normal population. Nonetheless, a patient with a large spleen below the costal margin should be cautioned against contact sports or other activities known to lead to blunt trauma to the abdomen

Treatment

• 1.

  Folic acid supplement (1 mg/day).

• 2.

  Leukocyte-depleted packed red cell transfusion for severe erythroblastopenic crisis.

• 3.

  Splenectomy for moderate-to-severe cases (see Table 7.1 ). Most patients with less than 80% of normal spectrin content require splenectomy. Splenectomy should be carried out early in severe cases but not before 5 years of age, if possible. The management of the splenectomized patient is detailed in Chapter 5 , Lymphadenopathy and Diseases of the Spleen. Although spherocytosis persists postsplenectomy, the red cell life span normalizes and complications are prevented, especially transient erythroblastopenia and hyperbilirubinemia. There may, however, be an increased risk of arterial and venous thrombosis in later life as well as an increased risk for idiopathic pulmonary hypertension. Patients are at risk of sepsis after splenectomy, especially for those under 5 years of age. In partial splenectomy, up to 90% of the splenic mass is removed with small studies suggesting that the technique leaves enough splenic tissue to protect against infection. The technique is not widely utilized but its use should certainly be entertained in transfusion-dependent patients who are under 5 years of age. It is being offered more frequently as an elective alternative to full splenectomy in patients in the moderate-to-severe category. There may be an increased risk for iron loading in patients with HS who have not undergone splenectomy. Since patients in this situation are unlikely to tolerate phlebotomy, iron overload may make the decision for splenectomy or even partial splenectomy even more complex. Laparoscopic splenectomy is safe in children. Although it requires more operative time than open splenectomy, it is superior with regard to postoperative analgesia, smaller abdominal wall scars, duration of hospital stay, and more rapid return to a regular diet and daily activities. It is not known whether accessory spleens are readily identified with the laparoscope although the magnification afforded by the laparoscope might be advantageous in some cases.

• 4.

  Ultrasound should be carried out before splenectomy to exclude the presence of gallstones. If present, cholecystectomy is also indicated.

Genetics

HE is characterized by an autosomal dominant or codominant mode of inheritance with variable penetrance, affecting about 1 in 25,000 of the population. The prevalence of HE is much higher in regions where malaria is endemic. This could be explained by the resistance of elliptocytes to malarial invasion.

Occasionally, patients who are severely affected appear to be the offspring of a family with only a single affected parent. In this case a “silent carrier”–like mutation in an α-spectrin gene of the unaffected parent may be the cause.

Pathogenesis

HE is due to various defects not only in the skeletal proteins, spectrin, and protein 4.1, but also in the integral protein glycophorin C. The basic membrane defects consist of

• defects of spectrin self-association involving the α-chains (65%)

• defects of spectrin self-association involving the β-chains (30%)

• deficiency of protein 4.1

• deficiency of glycophorin C

• “silent carrier” effect: α-spectrin mutant genes which produce less α-spectrin when paired with an α-spectrin structural mutant. They lead to more severe disease (see next).

The mechanically unstable membrane of HE leads to shape change from discocyte to elliptocyte as the membrane is buffeted by shear stress in the circulation.

Patients who are heterozygotes for these defects have milder disease while double heterozygotes and homozygotes for these mutants have progressively more severe syndromes.

Hematologic features

• Blood smear: 25–90% of cells have elongated oval elliptocytes

• Osmotic fragility is normal or increased

• Autohemolysis is usually normal but may be increased and usually corrected by the addition of glucose or ATP.

Clinical features

• Varies from patients who are symptom-free to severe anemia requiring blood transfusions. The percentage of microcytes best reflects the severity of the disease

• About 12% have symptoms indistinguishable from HS

• The percentage of elliptocytes varies from 50% to 90%. No correlation has been established between the degree of elliptocytosis and the severity of the anemia.

Classification

HE has been classified into the following clinical subtypes:

• 1.

  Common HE, which is divided into several groups:

  • a.

    silent carrier state

  • b.

    mild HE

  • c.

    HE with infantile pyknocytosis

• 2.

  Common HE with chronic hemolysis, which is divided into two groups:

  • a.

    HE with dyserythropoiesis

  • b.

    homozygous common HE, which is clinically indistinguishable from HPP (see later discussion)

• 3.

  Spherocytic HE, which clinically resembles HS; however, a family member usually has evidence of HE

• 4.

  Southeast Asian ovalocytosis, in which the majority of cells are oval. Some red cells contain either a longitudinal or transverse ridge

• 5.

  Infantile hemolytic elliptocytosis of infancy: these patients present with hemolytic elliptocytosis (mimicking HPP) that changes over the first 2 years of life to a clinical picture of mild HE as fetal hemoglobin changes to adult hemoglobin. Usually, there is a single affected parent with HE.

Treatment

The indications and considerations for transfusion, splenectomy, and prophylactic folic acid are the same as for HS.

Genetics

Homozygous or doubly heterozygous for spectrin chain mutants (e.g., Sp-a ^1/74 and Sp-a ^1/76 ). The spectrin chain defects found in HPP are similar to those found in HE.

Pathogenesis

HPP is a congenital hemolytic anemia associated with in vivo red cell fragmentation and marked in vitro fragmentation of red cells at 45°C. Because of the similarities in the membrane defect in this condition and HE, it is viewed as a subtype of HE.