thalassemia

thalassemia
Field	Hematology

thalassemia. It is a group of inherited blood disorders characterized by abnormal hemoglobin production, leading to the destruction of red blood cells and anemia. The conditions are caused by mutations in the genes that code for the globin protein subunits of hemoglobin. The severity of the disorder varies widely, from asymptomatic to life-threatening, depending on the specific genetic mutations involved.

Signs and symptoms

Clinical presentation ranges from mild microcytic anemia to severe complications requiring lifelong medical care. Individuals may experience fatigue, weakness, pallor, and jaundice due to hemolytic anemia. Severe forms often present in early childhood with failure to thrive, hepatosplenomegaly, and bony deformities such as frontal bossing resulting from bone marrow expansion. Complications can include growth retardation, delayed puberty, and endocrine disorders like diabetes mellitus and hypothyroidism. Iron overload, often a consequence of repeated blood transfusions, can lead to damage in the liver, heart, and endocrine glands, manifesting as cirrhosis, cardiomyopathy, and arrhythmias.

Causes and genetics

The disorders result from mutations in the HBB gene on chromosome 11 or the HBA1 and HBA2 genes on chromosome 16, which encode the beta and alpha globin chains of hemoglobin, respectively. These genetic defects are inherited in an autosomal recessive manner. The alpha-thalassemia trait is often associated with deletions of one or more of the four alpha-globin genes, while beta-thalassemia is frequently caused by point mutations affecting the beta-globin gene. The high frequency of these alleles in certain populations is attributed to heterozygote advantage against malaria, a phenomenon also observed with sickle cell disease. Notable research into the molecular genetics has been conducted at institutions like the National Institutes of Health and the Wellcome Sanger Institute.

Diagnosis

Diagnosis typically involves complete blood count (CBC) findings of microcytic, hypochromic anemia, and specific tests like hemoglobin electrophoresis to identify abnormal hemoglobin variants such as Hemoglobin H or elevated levels of Hemoglobin A2 and Hemoglobin F. Genetic testing can identify specific mutations and is used for prenatal diagnosis through procedures like chorionic villus sampling or amniocentesis. Peripheral blood smear examination may reveal target cells, nucleated red blood cells, and basophilic stippling. Differential diagnosis includes other causes of microcytic anemia like iron deficiency anemia and anemia of chronic disease.

Management

Management is supportive and varies by severity. Regular blood transfusions are the mainstay for severe forms to maintain hemoglobin levels, but this leads to iron overload, necessitating treatment with iron chelation therapy using agents like deferoxamine, deferiprone, or deferasirox. Hematopoietic stem cell transplantation from a compatible donor, often a sibling, is the only curative therapy. Splenectomy may be performed in cases of hypersplenism. Folic acid supplementation is commonly given. Research into gene therapy, such as trials using lentiviral vectors, offers potential future treatments, with work advanced by organizations like Bluebird Bio and research published in journals like *The New England Journal of Medicine*.

Epidemiology

The disorders are most prevalent in tropical and subtropical regions, aligning with historical malaria endemicity. High-frequency areas include the Mediterranean Basin, Sub-Saharan Africa, the Middle East, the Indian subcontinent, and Southeast Asia. According to the World Health Organization, millions of people are carriers, with significant public health impacts in countries like Cyprus, Sardinia, Greece, Thailand, and Cambodia. Migration patterns have spread the gene pool to regions like North America and Northern Europe. The Cooley's Anemia Foundation in the United States provides support and advocacy for affected individuals.

History

The condition was first described clinically by Thomas Benton Cooley and Pearl Lee in Detroit in 1925, who reported a form of severe anemia in children of Mediterranean descent, later termed Cooley's anemia or beta-thalassemia major. The term "thalassemia" derives from the Greek language words for "sea" and "blood," coined by George Hoyt Whipple. The genetic basis and molecular heterogeneity began to be unraveled in the mid-20th century by scientists including Vernon Ingram and James V. Neel. The protective effect against malaria was elucidated by J.B.S. Haldane, forming part of his malaria hypothesis. Landmark advances in management included the introduction of desferrioxamine for iron chelation by M. Barry and the first successful bone marrow transplant for the disease performed in Seattle.

Category:Hematology