Hematology - Hemoglobinopathies

QUALITATIVE: a.a. substitutions/deletions cause structural change in globin chain
QUANTITATIVE: genetic defects causing decr. synthesis of normal globin chains (thalassemias)
COMBINED DISORDERS: individ. is doubly heterozygous for 2 structural variants or str. var. & a thalassemia

-Most common hemoglobinopathy
-Most prevalent in central africa, and in African-Americans
-Autosomal recessive
-Caused by single base mutation in 6th aa on the β-globin chain causing substitution of valine for glutamic acid

HbS polymerizes under reduced O2 tension making tactoids. Rigid sickle-shaped RBCs result, causing hypoxia & infarctive crises that can be painful. Recurrent deformations of RBC can lead to permanent sickle shape or hemolysis, reducing lifespan of cell

APLASTIC crisis: bone marrow overworked as result of stress to produce new RBCs
HEMOLYTIC crisis: ACUTE increase in severity of existing anemia
VASO-OCCLUSIVE/PAINFUL crisis: hallmark of Sickle cell anemia, episodes of pain caused by blockage of microvasculatue by sickled cells

1st signs appear around 6 mos age (correlates w/ transition to b-chain)
reduced RBC life span (10-20 days!)
Chronic hemolytic anemia w/ many complications

SEVERE anemia (Hb only 6-8 g/dL)
normocytic, normochromic
aniso, poik, target cells, schizocytes, drepanocytosis, Howell-Jolly, Pappenheimer, polychromasia

SCREENING TESTS: solubility tests (Sickledex/Sicklesol)
-tube test precipitates abnormal HbS, making soln turbid
DEFINITIVE: cellulose acetate electrophoresis, citrate agar electrophoresis

Heterozygous condition, most common in US (~8% african americans)

Pt's usually asymptomatic but sickling potential still exists

NORMAL peripheral blood smear
Screening tests POSITIVE
some HbS on electrophoresis

Common in West African blacks
Small % of African Americans affected

aa substitution on beta chain (Lysine for glutamic acid)
decrease in Hb solubility; intracellular crystals form (bars of gold)
RBC's become rigid

Pt's asymptomatic but joint/abdominal pain possible.
splenomegaly
chronic hemolytic anemia

MODERATE anemia
NORMOCYTIC, NORMOCHROMIC
codocytes, HbC crystals possible (bars of gold)
slight increased retics
Electrophoresis confirms HbC disease

2-3% American blacks affected
Pt's asymptomatic
electrophoresis to confirm

a. both β-chains abnormal (substituted w/ 2 different a.a's)
b. resembles mild sickle cell anemia
c. target, folded RBC's on smear (clam shaped)
d. POSITIVE screening tests
e. electrophoresis shows abnormal Hgb

a. person has structural Hb variant (HbS) AND a quantitative defect
b. severity of clinical & lab findings depends on severity of thalassemia inherited
1. β0 thalassemia produces no β-chains
2. β+ produces less β-chains

disorders characterized by precipitation of denatured abnormal Hbs as artifacts called HEINZ BODIES

consisted of denatured hemoglobin
attach to inner surface of RBC membrane, affecting permeability and decreasing deformability
inclusions pitted by splenic macrophages leaving cell w/ less Hb and membrane => eventual RBC destruction

problems result from aa substitutions that affect stability of hemoglobin molecule.
-substitution of aa around heme pocket
-" at contact pts between α & β chains
-" of polar for nonpolar aa
-deletions or elongations of 1° structure

1. INHERITED disorder
2. ALL Pt's heterozygous
3. Severity of anemia depends on degree of instability of the Hb molecule

1. Heat Instability Test
-always POSITIVE w/ unstable Hb's
-fine precipitate from hemolysate of RBCs heated @50C for 60min. (precip=unstable)
2. Isopropanol Stability Test
-unstable Hb's precip in 20min in presence of nonpolar isopropanol
3. Heinz bodies present w/supravital stain

-bind O2 more readily => less release to tissue
-left shift in O2 dissoc curve
-Don't result in anemia; [Hgb] and Hct increase to compensate

-release O2 very easily to tissue
-right shift in O2 dissoc curve
-normal to decreased [Hgb] and slight anemia