Hereditary Spherocytosis

Article written and reviewed by Dr Luca Moretti

hereditary spherocytosis is one of the most common causes of congenital hemolytic anemia in Western countries and is characterized by spherical red blood cells, or spherocytes, and structural abnormalities of red-cell membrane proteins. This disorder increases the risk of chronic hemolysis, particularly in the spleen, and has a broad clinical spectrum ranging from minimally symptomatic forms to severe variants complicated by profound anemia and neonatal jaundice.

Hereditary spherocytosis is transmitted predominantly through autosomal dominant inheritance, although rarer and generally more severe autosomal recessive forms have also been described. Prevalence is particularly high in populations of Northern European ancestry, in which hereditary spherocytosis is the most common inherited hemolytic anemia. Timely diagnosis is essential for managing acute and chronic complications, promptly recognizing and managing aplastic crises, and planning possible therapeutic interventions such as splenectomy.

The effect on quality of life and life expectancy depends on the severity of the molecular defect, the effectiveness of compensatory hematopoietic mechanisms, and multidisciplinary management of complications, with particular attention to infectious and thrombotic risk after splenectomy.

Etiology

hereditary spherocytosis is caused by mutations affecting genes that encode the major red-cell membrane proteins required to maintain the biconcave structure and mechanical stability of red blood cells. The genes most frequently involved encode spectrin (SPTA1, SPTB), ankyrin (ANK1), band 3 (SLC4A1) and protein 4.2 (EPB42).

These mutations cause quantitative or qualitative defects in these proteins, with loss of cohesion between the cytoskeleton and the membrane lipid bilayer. Progressive loss of cell surface area follows, producing smaller, rounder and less deformable red blood cells called spherocytes, which are particularly susceptible to destruction in the spleen.

Inheritance is most often autosomal dominant; a minority of patients have autosomal recessive forms or de novo variants, with frequencies depending on the gene and population studied. Absence of a family history therefore does not exclude the diagnosis. Clinical expression may be extremely heterogeneous even within the same family, depending on the variant and the degree of impairment of the affected proteins.

Pathogenic variants most often involve ANK1, SPTB, SLC4A1, SPTA1 and EPB42, with variable distribution among populations. Abnormalities of SLC4A1 may be associated with impaired anion transport; the risk of gallstones is instead a consequence of chronic hemolysis and is not specific to any single protein defect.

Risk Factors and Prevention

Although hereditary spherocytosis is genetically determined, several conditions can modify the severity of clinical manifestations or promote complications. The main risk factors include:

• Positive family history: the presence of other cases of spherocytosis in the family increases the probability of transmitting the disease to descendants
• Recessive variants or compound heterozygosity involving different red-cell membrane genes
• Concomitant folate deficiency, vitamin B12 deficiency, or other conditions that reduce bone marrow erythropoietic capacity
• Exposure to viral infections , such as Parvovirus B19, which can induce acute aplastic crises
• Coexisting Gilbert syndrome, which increases the risk of gallstones

Prevention of complications relies on early diagnosis, folic acid supplementation in moderate or severe forms, prevention of infections, and careful assessment of the indication for splenectomy, especially in children and patients at risk of severe infections.

Pathogenesis and Pathophysiology

The pathogenesis of hereditary spherocytosis is based on disrupted interactions between the cytoskeleton and the red-cell plasma membrane. Mutations in structural proteins cause progressive shedding of microvesicles from the cell surface, reducing the surface-area-to-volume ratio and transforming the classic biconcave red-cell shape into a spherical, less deformable configuration.

The resulting spherocytes cannot pass through splenic sinusoids without mechanical damage. The spleen acts as a physiologic filter for abnormal red blood cells and promotes their premature destruction through extravascular hemolysis. Red-cell survival falls from approximately 120 days to only days or weeks, triggering compensatory bone marrow erythropoiesis and release of reticulocytes into peripheral blood.

Chronic hemolysis progressively increases indirect bilirubin and the risk of jaundice and pigment gallstones . Disease severity depends on the balance between red-cell loss and marrow compensation: anemia may be minimal or absent in mild forms, whereas severe cases develop chronic hemolytic anemia that may require periodic transfusions or splenectomy.

Viral infections may worsen anemia; Parvovirus B19 can precipitate an acute aplastic crisis. Nutritional deficiencies may aggravate anemia but do not cause an aplastic crisis.

Clinical Presentation

The clinical presentation of hereditary spherocytosis is extremely variable and depends on the nature of the mutation, the amount and residual function of red-cell membrane proteins, and the effectiveness of compensatory erythropoiesis. The disease may present in early childhood but can remain unrecognized until adulthood in milder forms.

Most patients have chronic hemolytic anemia of mild to moderate severity, accompanied by intermittent jaundice and splenomegaly. In infants and young children, diagnosis may follow prolonged neonatal jaundice or anemia unresponsive to iron therapy. Severe forms present with severe anemia, growth delay, marked fatigue and a need for repeated transfusions.

The most common clinical findings are:

• Mucocutaneous pallor from chronic anemia
• Mild to moderate jaundice due to increased indirect bilirubin
• Splenomegaly often mild to moderate, but sometimes massive in severe disease
• Pigment gallstones which may develop during childhood and cause colic, abdominal pain, or infectious complications
• Episodes of acute hemolytic crisis, especially during infections

In milder forms, diagnosis may be incidental during evaluation for mild anemia, jaundice, or family history. Persistent microcytosis warrants investigation for a concomitant cause.

A characteristic complication is the aplastic crisis, triggered especially by infection with Parvovirus B19. Other complications include hemolytic crises, marked jaundice, and cholecystitis or cholangitis caused by pigment stones.

Patients who have not undergone splenectomy may develop:

• Progressive splenic enlargement with risk of hypersplenism and associated thrombocytopenia or leukopenia
• Constitutional symptoms such as chronic fatigue, easy fatigability, and irritability in children

The natural history of hereditary spherocytosis is strongly influenced by the severity of hemolysis, development of biliary complications, and management of aplastic and hemolytic crises.

Early diagnosis and multidisciplinary management allow normal growth and development in most patients, with good quality of life and reduced risk of long-term sequelae.

Diagnostic Evaluation

The diagnosis of hereditary spherocytosis is based on an integrated process beginning with clinical and laboratory suspicion and completed by morphological and functional characterization of red blood cells and, when appropriate, genetic testing. The goal is to distinguish spherocytosis from other hemolytic anemias and identify patients at risk of complications.

First-line diagnostic work-up:

• Complete blood count: usually shows normocytic anemia of variable severity with compensatory reticulocytosis. Significant microcytosis suggests iron deficiency or another concomitant condition.
• Peripheral blood smear: a key diagnostic element showing spherocytes small, round red blood cells lacking central pallor, together with poikilocytosis and polychromasia. In severe cases, spherocytes may constitute most circulating red blood cells.
• Markers of hemolysis: increased indirect bilirubin and LDH with reduced haptoglobin. Reticulocytosis is generally present but may be absent during an aplastic crisis or when the marrow response is inadequate.
• Direct antiglobulin test: typically negative; it is useful in the differential diagnosis of autoimmune hemolytic anemia, although it does not absolutely exclude rare DAT-negative forms.

Specific second-line tests:

• Osmotic fragility test: osmotic fragility is characteristically increased, with spherocytes lysing at higher saline concentrations than normal red blood cells.
• Eosin-5-maleimide (EMA) binding test: supports the diagnosis with high sensitivity and specificity when integrated with the clinical picture, morphology, and other tests.
• Membrane protein electrophoresis: may characterize the protein defect in atypical cases; genetic or prenatal diagnosis requires molecular analysis.
• Molecular testing: indicated in complex familial cases, recessive forms, or for genetic counseling.

Diagnosis results from integration of clinical and family history, hemolysis indices, red-cell morphology, and screening tests such as eosin-5-maleimide binding or ektacytometry; no single finding is diagnostic in every case. Genetic testing can help confirm the diagnosis, characterize the variant, and provide family counseling.

Differential diagnosis: The main differential diagnoses include:

• Autoimmune hemolytic anemia: may occur at any age, can show spherocytes on the blood smear, and is generally associated with a positive direct antiglobulin test, although rare DAT-negative forms exist. Distinction requires integration of the history, DAT, and clinical and laboratory findings.
• Other hemoglobinopathies and enzyme disorders: such as pyruvate kinase deficiency and glucose-6-phosphate dehydrogenase deficiency
• Other membranopathies: hereditary elliptocytosis, stomatocytosis, and ovalocytosis

Recognition of family history, the typical clinical picture, and the combination of laboratory findings are essential for correct diagnostic classification.

Timely diagnosis allows appropriate follow-up, prevention of complications, and individualized treatment strategies according to disease severity and risk.

Treatment and Prognosis

Treatment of hereditary spherocytosis is individualized according to clinical severity, age, complication frequency, and specific risk factors. The main goals are to prevent acute hemolytic crises, support normal growth and development in children, reduce the risk of biliary complications, and optimize quality of life. Management requires multidisciplinary follow-up involving the pediatrician, hematologist, and, in selected cases, surgeon.

Supportive treatment:

• Folic acid supplementation: indicated mainly in moderate or severe disease, during periods of increased requirement, or when deficiency is present; it does not prevent Parvovirus B19 aplastic crises.
• Red-cell transfusions: indicated only in severe disease, for uncompensated symptomatic anemia or during acute aplastic crises, particularly in young children.
• Treatment of biliary complications: cholecystectomy should be considered for symptomatic gallstones, recurrent colic, or infectious complications.
• Management of hemolytic and aplastic crises: close hematologic monitoring, transfusion support, and treatment of underlying infections.

Regular clinical and laboratory surveillance is a central component of management, with periodic assessment of the blood count, reticulocyte count, liver function, and signs of gallstones.

Splenectomy: Splenectomy is a selective treatment for moderate or severe disease with symptomatic anemia, hypersplenism, or transfusion requirements. It improves anemia and prolongs red-cell survival but does not correct the membrane defect. Because it increases the risk of infection by encapsulated bacteria and thrombosis, it should preferably be performed after 5 years of age and only in carefully selected cases.

Complete vaccination is mandatory and prolonged antibiotic prophylaxis is required after surgery in children.

Emerging therapeutic approaches: Gene and pharmacological therapies aimed at correcting molecular red-cell membrane defects or modulating splenic function are under study, but treatment currently remains predominantly supportive and preventive.

Prognosis: Prognosis is generally excellent in mild and moderate hereditary spherocytosis, with normal life expectancy and no major limitations. In severe disease, splenectomy can produce marked improvement in hemoglobin and quality of life, provided all measures to prevent infectious and thrombotic risk are implemented. The most concerning complications are aplastic crises and severe post-splenectomy infections.

Prevention of complications relies on early diagnosis, education of patients and families about warning signs, periodic monitoring, and close collaboration among the specialists involved.

Complications

The complications of hereditary spherocytosis are major causes of morbidity and, if not promptly recognized and managed, can adversely affect long-term prognosis. Chronic hemolysis and splenomegaly, sometimes associated with hypersplenism, expose patients to specific risks at every age.

Hematologic complications:

• Acute aplastic crises: typically triggered by Parvovirus B19 infection, causing an abrupt fall in red-cell production and severe anemia that often requires urgent transfusion.
• Hemolytic crises: especially during infections, with acute worsening of anemia and increased bilirubin.

Biliary complications:

• Pigment gallstones are very common even during childhood and may cause colic, cholecystitis, cholangitis, and pancreatitis.
• Biliary tract infections, especially in patients who have not undergone cholecystectomy.

Infectious complications: After splenectomy, the risk of overwhelming sepsis from encapsulated bacteria remains elevated throughout life, particularly in children. Specific vaccination is required and, in pediatric patients, continuous antibiotic prophylaxis is needed during the first years after surgery.

Thromboembolic complications: Absence of the spleen is associated with increased risk of venous and arterial thrombosis, particularly in patients with other predisposing factors or a positive family history.

Nutritional and growth complications: Children with severe disease and chronically poorly compensated anemia may develop growth delay. Malnutrition and vitamin deficiencies are not intrinsic complications and should be investigated and treated as separate conditions.

Overall, management of complications in hereditary spherocytosis requires an individualized, proactive approach with careful surveillance, education of patients and parents, and prompt intervention when signs of deterioration appear.

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