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Thalassemias

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Topic updated on 09/09/17 7:10pm

Snap Shot
  • A 22-year-old Vietnamese female presents for a routine gyn exam. Her menstrual cycle is normal and there is no evidence of other bleeding. Guiac is negative. Her hemoglobin is at 11 (12-16), RBC is 5.8 (3.5-5.5), and an MCV of 70 (80-100) with a normal RDW of 10.  WBC and platelets are normal. Hemoglobin electrophoresis shows an increase in amount of Hgb A2 and Hgb F.
Introduction

  • Hereditary disease caused by decreased production of hemoglobin chains
  • Most common cause of microcytic anemia in Asian Americans and African Americans
  • There are four alpha genes and two beta genes that make up three forms of hemoglobin (Hgb)

    Hgb Form
    Subunits
    Prevalence
    Hgb A alpha, alpha, beta, beta 96-98% of adult hemoglobin
    Hgb A2 alpha, alpha, delta, delta Present in trace amounts in adults
    Hgb F alpha, alpha, gamma, gamma
    Declines in the first year of life
Evaluation
  • Forms of disease diagnosed through gel-electrophoresis of globin chains
  • Unexplained finding is that although there is a decrease in the Hgb concentration and MCV,  there is a normal or slightly increased RBC count
  • Ratio used:
    • Mentzer Ratio = MCV / RBC
      • if it is less than 13 it is highly predictive of thalassemia
      • greater than 13 indicates an iron deficiency or anemia of inflammation
Alpha Thalassemia
  • Due to a decrease in alpha globin chain production
  • Seen commonly in Asians
    • less common in Africans and Mediterranean
Affected alleles
Disease
Characteristics
Evaluation
1/4
Carrier state
Asymptomatic
Normal
2/4
Alpha Thal. minor
Normal life expectancy
Mild microcytic anemia
3/4
Hgb H disease
Associated with chronic hemolytic anemia, pallor, and splenomegaly. May require occasional transfusion
Hgb H (beta tetramer) and Bart's Hgb (gamma tetramer) on electrophoresis
4/4
Hydrops fetalis
Fetal demise with total body edema
Bart's beta-4 Hgb precipitations

Beta Thalassemia
  • Beta thalasemia is more common in people of Mediterranean or African origin
  • Function of beta chain required at six months when switch from fetal Hgb to adult beta Hgb occurs
Affected alleles
Disease
Characteristics
Evaluation
Treatment
1/2
Thalassemia minor 
Asymptomatic carrier
Decreased Hgb A, increased Hgb A2(y) and normal Hgb F
Avoid oxidative stress, treat with folate and transfusions during severe anemia and pregnancy
2/2
Thalassemia major
Anemia develops at six months as Hgb F declines, frontal bossing from extramedullary hematopoiesis, and splenomegly
No Hgb A,  increased Hgb A2, and Hgb F on electrophoresis
Splenectomy, folate supplementation, and transfusions. Symptoms improve with transfusions, patients usually die from transfusion iron overload (heart and liver failure).



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