04 Hemoglobin Hemoglobinopathies

7/28/2019 04 Hemoglobin Hemoglobinopathies

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Hemoglobinopathies


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Hemoglobinopathies (Qualitative)

Hereditary Disorders

Abnormal Hgb Structure

> 300 Types Abnormal Hgb (Hgb S Disorders - MostPrevalent

Molecular abnormalities in hemoglobinopathies Substitution of one amino acid for another (most common)

Substitution of more than one amino acid

Deletion of one or more amino acids Fusions of hemoglobin chains

Extension of an amino acid chain


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Possible Consequences of a

Hemoglobinopathy No detectable effect

Instability of Hgb molecule (Unstable Hgb)

Increase or a decrease in O2 affinity

Inability to maintain iron in its reduced

state (methemoglobinemia)

Dec solubility of hgb molecule


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Hemoglobin M Disease

Substitution at either proximal or distal histidine

loci (his tyr) iron-phenolate complex

Fe+++ state is incapable of binding O2

cyanosis

Methemoglobinemia


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Unstable Hemoglobinopathies

Mostly mutation in heme pocket region

H2O gains access to hydrophobic region

Result: heme instability, denaturation & releaseof heme from its binding site

Heinz Bodies evidence of an unstable hgbmutant


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Hemoglobinopathy Altering Oxygen

Affinity Increased O2 Affinity:

Stabilization of Oxy-

conformation = inc O2

affinity

Confirmed by left shift O2

Saturation Curve

Typically exhibit

erythrocytosis

Decreased O2 Affinity:

Stabilization of Deoxy-

conformation = dec O2

affinity

Confirmed by right shift

O2 Saturation Curve

Typically somewhat

anemic


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HEMOGLOBINOPATHIES

Hb E (GLULYSINE 26TH BETA)AGAR GEL E AT ACID Ph

UNSTABLE IN OXIDANT EXPOSURE

Very low MCV (55-65 fL) Few to many codocytes

Hb MA OR B- CHAIN MUTATION IN HIS TYR RESIDUE

OF HEME POCKETAutooxidation of iron to Fe3+) methemoglobin

(+) SCHUMMS TEST


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Hgb C-Harlem (C-Georgetown) double sub at B

chain

6th

valine for glutamic acid 73rd aspartic acid for asparagine (Korle Bu mutation)

Hgb D & G:

Group of beta & alpha chain variants that migrate in

an alkaline pH at the same electrophoretic position asHgB S


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Hgb O-Arab:

121st B chain lysine for glutamic acid

Mild hemolytic anemia; many codocytes

The only HgB to move just slightly away from

the point of application toward the cathode on

citrate agar at an acidic pH


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Clinically Significant Variant HemoglobinsHemoglobinopathy Alpha Beta Comments

Hemoglobin S a2bS

2 Normal Defective

Hemoglobin C a2bC

2 Normal Defective Hemolytic anemia, splenomegaly,

target cells are characteristic

Hemoglobin E a2bE2 Normal Defective Benign, common in SE Asia

Hemoglobin Constant

Spring

HCSpr Defective Normal Long alpha chain

Hemoglobin H b4 Absent Normal Paucity of alpha chains

Screening test: Heat instability testHemoglobin Barts g4 Absent Normal Not compatible with life

Hemoglobin M Normal Normal A group of abnormal hemoglobins in

which a single amino acid

substitution favors the formationof methemoglobin.


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HEREDITARY PERSISTENCE OF

Hb F PARTIAL/ TOTAL SUPPRESSION OF

BETA & DELTA CHAINS

Lab Dx:

ALKALI DENATURATION TEST

KLEIHAUER- BETKE (ACID

DENATURATION TEST)


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KLEIHAUER- BETKE (ACID

DENATURATION / Elution TEST) Principle:

Detects fetal-maternal hemorrhage

Blood smear + acid buffer (adult Hgb loses

Hgb into the buffer, only the stroma (cell

membrane) is left

Fetal RBCs unaffected & retain Hgb


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Fetal cells: bright pink

Adult cells: "ghost

cells

Cord blood is used as

the positive control


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Hemoglobinopathy S

AR

Chronic hemolytic

anemia Pallor,Jaundice, Dark urine,

HSM

Types:

Homozygous (Disease

or Anemia)

Heterozygous (Trait)

SC, SD, S-

THALASSEMIA

Homozygous: sickling

begins when O2

saturation < 85%

Heterozygous: sickling

begins when O2

saturation < 40%


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Hemoglobin S

Disorders Discovered 1904 man

from Grenada

Point Mutation

of B Globin Gene (146 aaof B globin chain)

Incidence: 8% in American Blacks

30% in Some African Confers resistance to P.

falciparum (Hgb S Trait)


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Complications

Hemolytic Crisis Hyperhemolytic crisis

Thrombotic crisis Heart infarction

CNS hemiplegia Mesentery abd. pain Sequestration crisis: Destruction of RBC in liver &

spleen shock HSM Aplastic crisis: Aplasia of BM

Hand-Foot Syndrome: children < 3 y/o w/ sickle cellanemia exhibit painful swelling in the hands and feet


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4 triggers of sickle cell crisis

Acidosis

Hypoxia

Infection

Fever


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Sickle Cell Anemia Lab Findings:

BM: erythroid hyperplasia

PBS: Marked poikilocytosis & anisocytosis

Drepanocytes

NRBCs Basophilic stippling

Pappenheimer bodies

Howell-jolly bodies

Moderate to marked polychromasia

Retic: 10-15%

High plt count & moderate neutrophilia

Low ESR

Low osmotic fragility test


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HEMOGLOBINOPATHY S LAB

DX:

PBS: SICKLE, BRONZE

ELLIPTOCYTES;

Normocytic

Normochromic

Reticulocytic count

BM exam: erythroid

hyperplasia


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HEMOGLOBINOPATHY S LAB

DX: SOLUBILITY TESTS (Na

DITHIONATE Test) Sickle Cell screening test

FALSE NEGATIVE in: Hgb


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Sickle Cell Disorders Diagnosis:

(+) SICKLING

PHENOMENON (Na

METABISULFIDETEST)

Sickledex - In Vitro

Sickling After Adding

Reducing Agt

Normal RBCs Sickled RBCs


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Sickle Cell Disorders Diagnosis:

Hgb Electrophoresis:ID Hgb S (Hb S- INC/Hb F- 1- 10% / Hb

A2- N) Sickle Cell

confirmation test

DNA Analysis -Prenatal Testing


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Treatment

During attacks: Rest in bed Hydration

Sedation

Antibiotics

Transfusion

Between attacks: Transfusion

Iron chelating agents

Splenectomy

Hydroxyurea

Butyrate

Increases proportion of HgB F inadults

Prognosis: Improve with age

Reactivate Fetal HemoglobinProduction using Hydroxyurea

Chemical inhibition of Hb Spolymerization

Increase in intracellular hydration

Altering RBC/Endothelial cellinteractions

BMT

Gene therapy


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HEMOGLOBINOPATHY C: Hb C

(GLU

LYSINE 6TH BETA) HGB C-A TRAIT:

ASYMPTOMATIC

Heterozygous HgBAC:

HgB C (30%)

HgB A (60%)


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HEMOGLOBINOPATHIES

HGB C-C DISEASE: NN anemia

Marked increased incodocytes (target cells)

Tetragonal crystals of HgBC on blood smear

Marked increase in retics

Homozygous HgB CC: Very little to no HgB A

HgB C (90%) HgB F (7%)

HgB A2 (3%)


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HgB SC lab findings:

NN anemia

HgB: 11 - 13 g/dL

Retic: 3 - 5%

PBS: Few sickle cells,codocytes, & intraerythrocyticcrystalline structures

Moderate hemolytic anemia

Moderate splenomegaly

Sodium dithionite test (+)


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WWW Sites of Interest

Joint Center for Sickle Cell and Thalassemic

Disorders: http://www-

rics.bwh.harvard.edu/sickle/ (Overview of sicklecell disease, thalassemia and iron kinetics)

The Sickle Cell Information Center, Emory

University:

http://www.emory.edu:80/PEDS/SICKLE/(Includes PowerPoint presentations on sickle

cell disease)


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Documents

04 Hemoglobin Hemoglobinopathies