Beta-thalassemia

Beta-thalassemia
Classification and external resources
ICD-10	D56.1
ICD-9	282.44
OMIM	141900
DiseasesDB	3087 1373
eMedicine	article/199534
MeSH	D017086

Beta-thalassemias (β-thalassemias) are a group of inherited blood disorders caused by reduced or absent synthesis of the beta chains of hemoglobin resulting in variable phenotypes ranging from severe anemia to clinically asymptomatic individuals. The total annual incidence of symptomatic individuals is estimated at 1 in 100,000 throughout the world. Three main forms have been described: thalassemia major, thalassemia intermedia and thalassemia minor. Individuals with beta thalassemia major usually present within the first two years of life with severe anemia, poor growth, and skeletal abnormalities during infancy. Affected children will require regular lifelong blood transfusions. Beta thalassemia intermedia is less severe than beta thalassemia major and may require episodic blood transfusions. Transfusion-dependent patients will develop iron overload and require chelation therapy to remove the excess iron. Bone marrow transplants can be curative for some children with beta thalassemia major.^[1] Transmission is autosomal recessive; however, dominant mutations have also been reported. Genetic counseling is recommended and prenatal diagnosis may be offered.^[2]

Types

Any given individual has two β globin alleles:

Name	Description	Alleles
Thalassemia minor	Only one of β globin alleles bears a mutation. Individual will suffer microcytic anemia. Detection usually involves lower than normal MCV value (<80 fL). Plus an increase in fraction of Hemoglobin A2 (>3.5%) and a decrease in fraction of Hemoglobin A (<97.5%).	β+/β or βo/β
Thalassemia intermedia	A condition intermediate between the major and minor forms. Affected individuals can often manage a normal life but may need occasional transfusions, e.g., at times of illness or pregnancy, depending on the severity of their anemia.	β+/β+ or βo/β
Thalassemia major	If both alleles have thalassemia mutations. This is a severe microcytic, hypochromic anemia. Untreated, it causes anemia, splenomegaly, and severe bone deformities. It progresses to death before age 20. Treatment consists of periodic blood transfusion; splenectomy if splenomegaly is present, and treatment of transfusion-caused iron overload. Cure is possible by bone marrow transplantation. Cooley's anemia is named after Thomas Benton Cooley.[3]	β+/βo or βo/βo or β+/β+

Note that β^o/β can be associated with β thalassemia minor or β thalassemia intermedia, and β⁺/β⁺ with thalassemia major or intermedia.

The genetic mutations present in β thalassemias are very diverse, and a number of different mutations can cause reduced or absent β globin synthesis. Two major groups of mutations can be distinguished:

• Nondeletion forms: These defects, in general, involve a single base substitution or small deletion or inserts near or upstream of the β globin gene. Most often, mutations occur in the promoter regions preceding the beta-globin genes. Less often, abnormal splice variants are believed to contribute to the disease.
• Deletion forms: Deletions of different sizes involving the β globin gene produce different syndromes such as (β^o) or hereditary persistence of fetal hemoglobin syndromes.

Testing, Treatment, and Complications

Thalassemia may co-exist with other deficiencies such as folic acid (or folate, a B-complex vitamin) and iron deficiency (only in thalassemia minor).

DNA analysis

This test is used to investigate deletions and mutations in the alpha- and beta-globin-producing genes. Family studies can be done to evaluate carrier status and the types of mutations present in other family members. DNA testing is not routinely done but can be used to help diagnose thalassemia and to determine carrier status. In most cases it is likely the treating physician will use a clinical prediagnosis by symptoms of anemia: tiredness, breathlessness, and poor exercise tolerance. Furthermore, abdominal pain due to hypersplenism and splenic infarction may occur and right-upper quadrant pain caused by gallstones may occur are major clinical manifestations. However, to coin thalassemiæ under signs and symptoms would be misleading when giving a diagnosis. Physicians will note these signs as associative due to the complexity of the nature of this disease. The following are also associative signs that can attest to the severity of the phenotype: pallor, poor growth, inadequate food intake, splenomegaly, jaundice, maxillary hyperplasia, dental malocclusion, cholelithiasis, systolic ejection murmur in the presence of severe anemia, and pathologic fractures. Based on a number of key symptoms tests are ordered for the differential diagnosis. These tests include CBC; Hemoglobin electrophoresis; Serum Transferin, Ferritin, Fe Binding Capacity; Urine urobilin & Urobilogen; Peripheral Blood Smear; Hematocrit; Serum Bilirubin. Further genetic analysis may include HPLC should routine electrophoresis prove difficult. But, before any of these tests are ordered, a physician should inquire into a detailed family history.^[4].

Thalassemia Major and Intermedia

Thalassemia major patients receive frequent blood transfusions that lead to iron overload. Iron chelation treatment is necessary to prevent iron overload damage to the internal organs in patients with Thalassemia Major. Because of recent advances in iron chelation treatments, patients with thalassemia major can live long lives if they have access to proper treatment. Popular chelators include deferoxamine and deferiprone. Of the two, deferoxamine is preferred; it is more effective and is associated with fewer side-effects.^[5]

The most common complaint by patients receiving deferoxamine is that it is difficult to comply with the subcutaneous chelation treatments because they are painful and inconvenient. The oral chelator deferasirox (marketed as Exjade by Novartis) was approved for use in 2005 in some countries. It offers some hope with compliance but is very expensive (~US$100 per day) and has been associated with deaths from toxicity.

Untreated thalassemia major eventually leads to death usually by heart failure; therefore, birth screening is very important. Bone marrow transplantation is the only cure for thalassemia, and is indicated for patients with severe thalassemia major. Transplantation can eliminate a patient's dependence on transfusions. If there is no matching donor for a child with thalassemia, a savior sibling can be conceived by preimplantation genetic diagnosis (PGD) to be free of the disease as well as match the recipient's human leucocyte antigen (HLA) type in order to be a donor for the sick child.

Thalassemia intermedia patients vary a lot in their treatment needs, depending on the severity of their anemia. All thalassemia patients are susceptible to health complications that involve the spleen (which is often enlarged and frequently removed) and gall stones. These complications are mostly prevalent to thalassemia major and intermedia patients.

Thalassemia Minor

Thalassemia minor is not always actively treated.^[6] Contrary to popular belief, thalassemia minor patients should not avoid iron-rich foods by default. A serum ferritin test can determine what their iron levels are and guide them to further treatment if necessary. Thalassemia minor, although not life-threatening on its own, can affect quality of life due to the effects of a mild to moderate anemia. Studies have shown that thalassemia minor often coexists with other diseases such as asthma^[7], and mood disorders^[8].

See also

• List of hematologic conditions

External links

• GeneReviews/NCBI/NIH/UW entry on Beta-Thalassemia

References

1. ^ HERBERT L. MUNCIE, JR., MD, and JAMES S. CAMPBELL, MD (15 August 2009). "Alpha and Beta Thalassemia". American Family Physician. http://www.aafp.org/afp/2009/0815/p339.html. Retrieved 29 September 2011. 
2. ^ Renzo Galanello; Origa, Raffaella (2010). "Beta-thalassemia". Pubmed Central 5: 11. doi:10.1186/1750-1172-5-11. PMC 2893117. PMID 20492708. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2893117. 
3. ^ http://www.whonamedit.com/synd.cfm/2157.html
4. ^ Orkin: Nathan and Oski's Hematology of Infancy and Childhood, 7th ed.. 
5. ^ Maggio A, D'Amico G, et al. (2002). "Deferiprone versus deferoxamine in patients with thalassemia major: a randomized clinical trial". Blood Cells Mol Dis 28 (2): 196–208. doi:10.1006/bcmd.2002.0510. PMID 12064916. 
6. ^ "Thalassemia: Treatments and drugs - MayoClinic.com". http://www.mayoclinic.com/health/thalassemia/DS00905/DSECTION=treatments-and-drugs. 
7. ^ Palma-Carlos AG, Palma-Carlos ML, Costa AC (2005). ""Minor" hemoglobinopathies: a risk factor for asthma". Allerg Immunol (Paris) 3 (5): 177–82. PMID 15984316. 
8. ^ Brodie BB (2005). "Heterozygous β-thalassaemia as a susceptibility factor in mood disorders: excessive prevalence in bipolar patients". Clin Pract Epidemiol Mental Health 1 (1): 6. doi:10.1186/1745-0179-1-6. PMC 1156923. PMID 15967056. http://www.cpementalhealth.com/content/1/1/6.