Disorders of Hemoglobbin Flashcards by Meghan May

Hemoglobin Disorders
• Structural variants
– Abnormal globin chain structure due to :
– Varied clinical effects depending on :

globin gene mutation

location and
nature of mutation in globin chains

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– Under-production of structurally normal globin chains
– Generally microcytic/hypochromic anemias of
varying severity

Thalassemias

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alpha globins located on chromosome ___

beta globins located on chromosome___

16 ( 2 sets thus 4 alleles)

11 (1 set, 2 alleles)

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Three normal hemogobin species in fetal and
postnatal life
– Hemolobin A:
– Hemoglobin F:
– Hemoglobin A2:

which dominates during fetal life?

What is composition 1 year after life?

– Hemolobin A: (alpha2beta2) 96% 1 year
– Hemoglobin F: (alpha2gamma2) 1%
– Hemoglobin A2: (alpha2delta2) 3%

HgF dominates during fetal life

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More than 500 structural hemoglobin variants have
been described
– Most are ________ in globin molecules
(due to single base pair substitutions in globin genes)
– Any globin gene may be affected
– Occasional other types of mutations

***most are clinically SILENT

single amino acid replacements

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Consequences of HgB structual abnormalities depends on:

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Possible consequences to structual hemoglobin abnormalities

– Sickling
– Instability
– Altered oxygen affinity (increased or decreased)
– Increased susceptibility to oxidation to methemoglobin
– Under-production

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What two common Lab test do we do for Dx of hemoglobin disorders?

Hemoglobin electrophoresis
– Gel
– Capillary
• High performance liquid chromatography
(HPLC)

~isloelectric focusing/Globin chain electrophorysis/ gene mutation analysis as well

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You decide to run Electorphoresis on pt suspected of HgB abnormality,

how is this typically performed?

What is HbA’s isoelectric point?

• Typically performed in parallel with alkaline and acid
buffers
• HbA has isoelectric point of 6.8

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How electrophoresis works:

– Negative charge in alkaline buffers–migrates toward :
– Positive charge in acid buffers–migrates toward :

Anode (+)

Cathode (-)

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In electrophoresis, migration of hemoblobin depends on what 2 factors?

– Net charge in alkaline electrophoresis
– Net charge and interaction with components of media in
acid electrophoresis

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How does HPLC work in a whole blood method (whole blood hemosylate)

– Hemoglobins adsorbed onto resin particles in column
– Different species differentially eluted based on affinity
for resin by gradually changing ionic strength of elution buffer
– Hemoglobins come off the column at highly
predictable retention times
• Some correlation with migration on alkaline electrophoresis

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Sickle Cell Disease
• Homozygous abnormality of the ____ globin chain
• ___to____substitution at amino acid 6
• Heterozygous HbS (S-trait) confers protection
against_____

beta

Glu to Val

malaria

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How common is Hb S gene?

– 4% allelic frequency for Hb S gene among AfricanAmericans
– Rare in other ethnic groups
• Homozygous S occurs at a frequency of 1 in 600
in African Americans

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Describe pathophysiology of SS anemia

• Deoxygenated HbS forms long polymers that distort the shape of the cell into an elongated, sickled form
– Intermolecular contacts involve abnormal valine at amino acid 6

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What does Hb S polymerization depend on?

• Extent of HbS polymerization is time and
concentration dependent

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Factors that affect concentration of HbS

• Percentage of hemoglobin S of total hemoglobin (homo vs heteroZ or if there are other Hb species~ like HbF
• Total hemoglobin concentration in the red cells (MCHC)
– Increased in cellular dehydration
– Decreased if co-existent thalassemia

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Time Dependence of Sickling
• Importance of transit time of red cells through ________ microvasculature

low oxygen tension

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Time Dependence of Sickling

Sickling enhanced in anatomic sites with _____ (e.g., spleen and bone marrow)
• Blood flow through microvasculature retarded in certain pathologic states like:

sluggish flow

– Inflammation

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Clinical Settings Predisposing
to Sickling

Hypoxia
Acidosis
Dehydration
Cold temperatures
Infections (multiple mechanisms)

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Why does acidosis predispose someone to sickling?

what about dehydration?

– Shift of oxygen dissociation curve to right, causing increased deoxygenation of Hb S

leads to hypertonicity leading to RBC dehydration

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• SS cells begin to sickle at ~___mm Hg
• Sickling is initially a_____ process, but
after multiple sickling/unsickling cycles,
membrane damage produces an irreversibly sickled cell
• RBC lifespan decreased to___ days

40mm Hg

reversible

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2 bad Effects of RBC Sickling

• Chronic hemolysis

• Microvascular occlusion with resultant tissue
hypoxia and infarction

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– Correlates with the number of irreversibly sickled cells

Chronic hemolysis in SS anemia

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Related to increased “stickiness” of SS red cells because of membrane damage

• Microvascular occlusion with resultant tissue hypoxia and infarction

SS anemia: * Newborns clinically fine because of \_\_\_\_ * Hematologic manifestations begin by \_\_\_\_ weeks of age * Clinical severity\_\_\_\_ from patient to patient

high HbF levels 10-12 variable

Clinical manifestations of SS anemia

Severe anemia Acte pain crisis from vaso-occusion Auto-spenectomy~~ shrunken spleeen, no functional Acute Chest Syndrome~ major cause of deaht Stokes

Auto-splenectomy in SS anemia: – Repeated episodes of \_\_\_\_\_\_\_, resulting in shrunken, fibrotic, nonfunctional spleen – Seen in essentially all adults with SS disease – Increased risk for infection by \_\_\_\_\_\_

splenic infarction encapsulated bacteria

– Severe complication, major cause of death in SS anemia – Result from pulmonary infections or fat emboli from infarcted marrow – Sluggish blood flow from inflammation causes sickling and vaso-occlusion, triggering vicious cycle

Acute chest syndrome

Strokes in SS anemia – Risk of stroke of 11% by age\_\_\_ – First clinical stroke most frequently occurs between ___ and \_\_\_years of age

20 2 and 8

Aplastic crisis seen in SS anemia: – Caused by acute decrease in \_\_\_\_ – Usually due to \_\_\_\_\_infection

RBC production parvovirus B19 : Infects erythroid precursors and cause red cell aplasia with absent erythropoiesis for 7-10 days

– Acute pooling of blood in spleen – Precipitous drop in hemoglobin – Potential for hypovolemic shock

• Splenic sequestration crisis seen in SS anemia

Megaloblastic anemia in SS anemia caused by Folate consumption because of

chronic erythroid hyperproliferation

More clincal manifestations of SS anemia

* Growth retardation * Bony abnormalities * Renal dysfunction * Leg ulcers * Cholelithiasis

SS anemia Lab Findings: \_\_\_\_ bilirubin \_\_\_\_MCV \_\_\_\_\_reticulocytes

SS anemia: Increased bilirubin Normal MCV increased reticulocytes

Describe what you would see on a PB smear in pt with SS anemia

Sickled cells Target cells polychromasia

Pt with chronic SS anemia will have what kind of HgB?

steady state from 5-11 (most common around 7)

• Hemoglobin SC disease – Compound\_\_\_\_\_ state – Hemoglobin C results from \_\_\_\_\_substitution at the 6th amino acid of the beta globin chain

heterozygous glu to lys

which is worse; Hb SC or Hb SS? What are HgB levels like in both diseases?

Hb SC is milder with HgB = 10-12 SS anemia ~ 7

Hb S/Beta thalassemia – Heterozygous Hb S with trans beta thalassemia allele, resulting in:

decreased or absent production of normal beta chains

Describe symptomatology and labs seen in HbS/Beta thalassemia

– Ranges from asymptomatic to a disorder nearly identical to SS disease, depending on output of normal beta chains from thalassemia allele – Lab findings: Hb S \> Hb A

How do we manage pts with SS anemia?

* Newborn screening * Infection prophylaxis * Supportive care for acute manifestations * Hydroxyurea * Regular red cell transfusions * Allogeneic stem cell transplant

Hydroxyurea – Chemotherapy agent used to \_\_\_\_\_\_in myeloproliferative neoplasms – Inhibits \_\_\_\_\_ and causes cell cycle arrest – Increases erythrocyte levels of\_\_\_\_, ameliorating the sickling manifestations

reduce blood cell counts ribonucleotide reductase HbF

Benefits of hydroxyurea for pts with SS anemia

– Dramatically reduces frequency of pain crises, as well as significantly decreased transfusion requirements, hospital admissions, incidence of acute chest sydrome

SS anemia outcomes Median age of death of\_\_\_ for males and\_\_\_ for females with SS disease • Gains mainly seen due to decreased mortality rates in children due to aggressive infection prophlaxis and comprehensive care approaches • No apparent decrease in mortality rates in adults over last several decades

42, 48

Major causes of death in adults with SS anemia

• Major causes of death in adults: – Liver dysfunction – Pulmonary hypertension – Stroke – Vaso-occlusive crisis – Acute chest syndrome

S-trait seen in \_\_\_% of AA and has what clinical significance?

S-Trait • 8% of African Americans • Clinically benign May be mild, sub-clinical kidney damage~ impaired urine conc or microhematuria

What do we see on Labs in pt w/ S trait?

– 60% Hb A, 40% HbS

Mild to moderate hemolytic anemia • Often asymptomatic • Splenomegaly – May cause occasional abdominal pain • 1/6000 African Americans

HbC disease or CC

HbC pathophysiology: * __ to ___ substitution of amino acid 6 of Beta chain * Cells abnormally\_\_\_\_\_\_ • RBC life span shortened to ____ days **• Not a sickling disorder**

Glu to Lys rigid and dehydrated 30-35

HbC Disease-Lab Findings ~ what kind of cells on PBS ~ HgB levels

* Hemoglobin levels range from 8-12 g/dl * Numerous target cells * Mild microcytosis * Spherocytes * Occasional C crystals

In HbC, what is the % composition for: * HbC * HbA * HbF

* \>90% HbC * No HbA * \<7% HbF

* 2% of African-Americans * No anemia * Few target cells * 50-60% HbA, 30-40% HbC

HbC Trait

Group of inherited disorders characterized by decreased production of structurally normal globin chains Highly heterogeneous both clinically and genetically

Thalassemias

Thalessemia seen in: Wide distribution in Mediterranean, Middle East, parts of India and Pakistan, and Southeast Asia

Beta-Thal

Thalessemia Occurs throughout Africa, Mediterranean, Middle East, and Southeast Asia

Alpha-thal

Thalessemias are usually: Macrocytic or microcytic normochromic or hypochromic

Decreased hemoglobin production produces **hypochromia** and **microcytosis** ## Footnote **– “Cytoplasmic maturation defect”**

In Thalessemias: Severity of hematologic manifestations is directly related to \_\_\_\_\_\_\_\_\_

the degree of chain imbalance ## Footnote *– Excess normally produced globin chains accumulate and cause intramedullary cell death and/or decreased RBC survival*

Beta Thalessemia: • Decreased beta globin chain production from affected alleles: is this more due to deletion or mutation?

MOre mutation, rarely deletion most often dt splicing errors

– Beta-thal major (Cooley’s anemia) – Beta-thal intermedia – Beta-thal minor How are these classified?

Classified clinically because of extreme genetic heterogeneity

Absence or marked decrease in beta-chain production on both beta alleles

Beta-Thal Major

In Beta Thal Major: – Excess of \_\_\_\_\_chains, which are unable to form tetramers, and precipitate in normoblasts and erythrocytes – Intramedullary cell death and decreased RBC lifespan

normal alpha

How do infants with Beta-Thal Major do?

• Infants well at birth--anemia develops over the first few months of life • Severe anemia-baseline Hb of **2-3** g/dL – Virtually *all Hb F* – Bizarre red cell morphology (hypochromia, targeting, erythroblastosis) \*\*\*Transfusion dependent

In Beta-Thal Major: Severity of clinical effects depends on what two things?

adequacy of transfusion program and efficacy of iron chelation

Inadequately transufsed Beta-Thal Major laundry list of issues:

• Stunted growth • Frontal bossing • “Mongoloid” facies • Increased skin pigmentation • Characteristic bony abnormalities • Fever • Wasting • Hyperuricemia • Spontaneous fractures • Hepatosplenomegaly • Infections • Folate deficiency • Death in childhood

Adequately Transfused B-Thal Major experience • Essentially normal early development • Avoidance of classic complications but also require:

Iron chelation therapy

What outcomes do we expect in pt receive adequate transfusions but without iron chelaiton with Beta-Thal Major?

Without adequate iron chelation therapy – Absence of pubertal growth spurt and menarche – Endocrine disturbances such as DM, adrenal insufficiency – Death from cardiac disease by end of third decade

With aggressive iron chelation therapy how do our outcomes change?

– Less severe cardiac disease and endocrine disturbances – Significantly improved life-span

• Heterozygous form • Asymptomatic • Discovered incidentally • Incidence – Common in Mediterranean and Asian populations – 1.5% of African Americans

Beta-Thal Minor

Labs in Beta-Thal Minor: HgB: Micro/macro/normocytosis PBS most important Diagnostic in labP

• Mild or no anemia (Hb\>~10g) • Microcytosis (50-70 fl) • Mild anisopoikilocytosis – Scattered target cells and Basophilic stippling **• Elevated HbA2: 3.5-7%**

if we see HbA2 elevated to 3.5-7 % what is this indicitive of?

Beta-Thal Minor

Alpha Thalassemias usually a result of:

gene DELETION

Alpha Thalassemias: Silent carrier = Alpha-Thal trait =

1 gene deleted 2 gene deleted w/ mild microcytic anemia simular to Beta-Thal minor

What happens when we have 3 alpha genes deleted?

Hemoglobin H disease (3 genes deleted) • Mild to moderate, chronic hemolytic anemia • Hb H represents beta tetramers – Does not effectively transfer oxygen • **Hb H soluble**, so does not initially precipitate in normoblasts (no intramedullary cell death) – Unstable over time, so precipitates in circulating red cells, causing hemolysis

What is hydrops fetalis?

``` Hydrops fetalis (4 alpha genes deleted) • Infants either stillborn or die within first few hours of life ```