beta-thalassemia

beta-thalassemia. It is a group of inherited blood disorders characterized by reduced or absent synthesis of the beta-globin chains of hemoglobin. This deficiency leads to microcytic anemia, ineffective erythropoiesis, and increased hemolysis. The clinical severity ranges from asymptomatic carrier states to severe, transfusion-dependent anemia presenting in early childhood.

Signs and symptoms

Clinical manifestations are highly variable and correlate with the degree of beta-globin chain deficiency. Individuals with **thalassemia major**, the most severe form, typically present in infancy with profound anemia, failure to thrive, and pallor. Chronic hemolytic anemia drives compensatory erythropoiesis, often resulting in hepatosplenomegaly and skeletal changes such as frontal bossing and maxillary hyperplasia. Complications from chronic blood transfusion therapy include iron overload, which can damage the liver, heart, and endocrine glands, leading to cirrhosis, heart failure, diabetes mellitus, and hypogonadism. Those with **thalassemia intermedia** have moderate anemia and may develop complications like extramedullary hematopoiesis and leg ulcers later in life, while **thalassemia minor** carriers are often asymptomatic or have mild microcytosis.

Genetics and pathophysiology

The disorder is caused by mutations in the HBB gene located on chromosome 11, which encodes the beta-globin subunit. Over 200 disease-causing mutations have been identified, including point mutations, small insertions, and deletions. These genetic lesions reduce (**β⁺**) or eliminate (**β⁰**) the production of beta-globin chains. The resulting imbalance between alpha-globin and beta-globin chains leads to the precipitation of unpaired alpha chains, forming inclusion bodies within developing erythroid precursors in the bone marrow. This causes ineffective erythropoiesis and premature destruction of red blood cells (hemolysis). The inheritance pattern is autosomal recessive; severe disease requires mutations inherited from both parents, while heterozygotes are typically carriers.

Diagnosis

Diagnosis involves a combination of hematological and molecular tests. Initial screening often includes a complete blood count (CBC) revealing microcytic, hypochromic anemia with a markedly reduced mean corpuscular volume (MCV). Hemoglobin electrophoresis or high-performance liquid chromatography (HPLC) is crucial, showing elevated levels of hemoglobin A2 (HbA2) and often hemoglobin F (HbF), with decreased or absent hemoglobin A (HbA). Peripheral blood smear examination may show target cells, basophilic stippling, and nucleated red blood cells. Confirmatory genetic testing identifies specific mutations in the HBB gene and is used for carrier screening and prenatal diagnosis, often via chorionic villus sampling or amniocentesis.

Management

Management is multidisciplinary and tailored to disease severity. For transfusion-dependent **thalassemia major**, the cornerstone is regular packed red blood cell transfusions, typically every 2-4 weeks, to maintain a hemoglobin level above 9-10 g/dL. This necessitates concomitant iron chelation therapy to prevent hemosiderosis; agents include deferoxamine (subcutaneous), deferiprone (oral), and deferasirox (oral). The only curative treatment is allogeneic hematopoietic stem cell transplantation (HSCT), with outcomes best in young patients with a matched sibling donor. For non-transfusion-dependent patients, management may include folic acid supplementation, occasional transfusions, and monitoring for complications. The novel agent luspatercept, which modulates TGF-β superfamily signaling, is approved to reduce transfusion burden. Splenectomy may be considered for significant hypersplenism.

Epidemiology

Beta-thalassemia has a high prevalence in tropical and subtropical regions, corresponding historically to areas endemic for falciparum malaria, as the carrier state confers a selective survival advantage. Major global hotspots include the Mediterranean Basin (particularly Italy, Greece, and Cyprus), the Middle East (including Iran and Saudi Arabia), South Asia (India, Pakistan, Bangladesh), and Southeast Asia. Significant carrier frequencies are also found in Africa and in diaspora populations worldwide. According to the World Health Organization, approximately 1.5% of the global population are carriers, with about 60,000 symptomatic individuals born annually. Public health initiatives like those by the Thalassemia International Federation focus on prevention through population screening and genetic counseling.