Contents

Search

alpha thalassemia

alpha-Globin gene synthesis is under control of 2 pairs of genes (total of 4). Four* alpha-thalassemias are: Classification: 1) alpha-thalassemia-2 trait (alpha-thalassemia silent carrier) a) deletion of a single alpha globin gene (there are 4 alpha globin genes. 2 on each chromosome) b) an asymptomatic carrier state 2) alpha-thalassemia-1 results from deletion or malfunction of 2 alpha globin genes. a) anemia is mild, microcytic & hypochromic b) cis form 1] deletion or malfunction of 2 genes on same chromosome 2] found in Asian & Mediterranean populations 3] hydrops fetalis found in these populations c) trans form 1] affected genes on different chromosomes 2] found in African American populations 3] hydrops fetalis unlikely 3) deletion or malfunction of 3 alpha globin genes a) hemoglobin H disease (beta-globin tetramers) b) moderately severe hemolytic anemia c) chronic transfusions usually not required 4) all 4 loci deleted or non-functional a) hemoglobin Bart's (gamma-globin tetramers) b) hydrops fetalis * - alpha/ alpha alpha (i.e. 3 of 4 functional alpha globin genes is referred to as silent thalassemia [2] Epidemiology: - occur mostly in Mediterranean & Southeast Asian populations Pathology: 1) imbalance in globin-chain production in adult hemoglobin A 2) alpha chain production can range from none to very nearly normal levels Laboratory: 1) complete blood count - microcytic anemia - RDW is normal (high in iron deficiency) [3] 2) peripheral smear - microcytosis, hypochromia, target cells 3) hemoglobin electrophoresis: normal - hemoglobin A2 band is not increased (unlike beta-thalassemia) [3] - there is no substitute for hemoglobin alpha chain 4) globin chain synthetic ratios 5) alpha thalassemia genotyping - HBA1 gene mutation - HBA2 gene mutation - HBA2 gene deletion Management: - alpha-thalassemia trait (alpha-thalassemia minor) requires no treatment [3]

Interactions

disease interactions

Related

alpha thalassemia genotyping alpha-globin gene alpha-thalassemia myelodysplasia syndrome X-linked alpha-thalassemia/mental retardation syndrome (ATR-X syndrome)

Specific

alpha thalassemia silent carrier alpha thalassemia-0 (homozygous alpha thalassemia) alpha thalassemia-1 (alpha-thalassemia trait, cis form) alpha thalassemia-2 (alpha-thalassemia trait, trans form) hemoglobin H disease

General

thalassemia

References

  1. Saunders Manual of Medical Practice, Rakel (ed), WB Saunders, Philadelphia, 1996, pg 585-86
  2. Harrison's Principles of Internal Medicine, 14th ed. Fauci et al (eds), McGraw-Hill Inc. NY, 1998, pg 651
  3. Medical Knowledge Self Assessment Program (MKSAP) 16, 17, 18. American College of Physicians, Philadelphia 2012, 2015, 2018.
  4. Harteveld CL, Higgs DR. Alpha-thalassaemia. Orphanet J Rare Dis. 2010 May 28;5:13 PMID: 20507641