TAILIEUCHUNG - Chapter 099. Disorders of Hemoglobin (Part 11)

Severity is highly variable. Known modulating factors are those that ameliorate the burden of unpaired α-globin inclusions. Alleles associated with milder synthetic defects and co-inheritance of α-thalassemia trait reduce clinical severity by reducing accumulation of excess α globin. HbF persists to various degrees in β-thalassemias. γ-Globin gene chains can substitute for βchains, generating more hemoglobin and reducing the burden of α-globin inclusions. The terms β-thalassemia major and β-thalassemia intermedia are used to reflect the clinical heterogeneity. Patients with β-thalassemia major require intensive transfusion support to survive. Patients with β-thalassemia intermedia have a somewhat milder phenotype and can survive without. | Chapter 099. Disorders of Hemoglobin Part 11 Severity is highly variable. Known modulating factors are those that ameliorate the burden of unpaired a-globin inclusions. Alleles associated with milder synthetic defects and co-inheritance of a-thalassemia trait reduce clinical severity by reducing accumulation of excess a globin. HbF persists to various degrees in 0-thalassemias. y-Globin gene chains can substitute for 0chains generating more hemoglobin and reducing the burden of a-globin inclusions. The terms 0-thalassemia major and 0-thalassemia intermedia are used to reflect the clinical heterogeneity. Patients with 0-thalassemia major require intensive transfusion support to survive. Patients with 0-thalassemia intermedia have a somewhat milder phenotype and can survive without transfusion. The terms 0- thalassemia minor and -thalassemia trait describe asymptomatic heterozygotes for pthalassemia. a-Thalassemia Syndromes The four classic a-thalassemias most common in Asians are a-thalassemia-2 trait in which one of the four a-globin loci is deleted a-thalassemia-1 trait with two deleted loci HbH disease with three loci deleted and hydrops fetalis with Hb Bart s with all four loci deleted Table 99-4 . Nondeletion forms of a-thalassemia also exist. Table 99-4 The aThalassemias Conditio n Hemoglo bin A Hemoglo bin H ß4 Hemoglo bin Level g L g dL MC V fL Normal 97 0 150 15 90 Silent thalassemia -a aa 98-100 0 150 15 90 Thalasse mia trait -a -a homozygous a-thal-2a or aa heterozygous a-thal-1a 85-95 Rare red blood cell inclusions 120-130 12-13 70- 80 Hemoglo bin H disease -- -a heterozygous a- thal-1 a-thal-2 70-95 5-30 60-100 6-10 60- 70 Hydrops fetalis 0 5-10è Fatal in utero or at birth

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