Disorders of Hemoglobbin Flashcards
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
– Under-production of structurally normal globin chains
– Generally microcytic/hypochromic anemias of
varying severity
Thalassemias
alpha globins located on chromosome ___
beta globins located on chromosome___
16 ( 2 sets thus 4 alleles)
11 (1 set, 2 alleles)
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
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
Consequences of HgB structual abnormalities depends on:
Possible consequences to structual hemoglobin abnormalities
– Sickling
– Instability
– Altered oxygen affinity (increased or decreased)
– Increased susceptibility to oxidation to methemoglobin
– Under-production
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
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
How electrophoresis works:
– Negative charge in alkaline buffers–migrates toward :
– Positive charge in acid buffers–migrates toward :
Anode (+)
Cathode (-)
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
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
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
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
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
What does Hb S polymerization depend on?
• Extent of HbS polymerization is time and
concentration dependent
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
Time Dependence of Sickling
• Importance of transit time of red cells through ________ microvasculature
low oxygen tension
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
Clinical Settings Predisposing
to Sickling
- Hypoxia
- Acidosis
- Dehydration
- Cold temperatures
- Infections (multiple mechanisms)
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
• 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
20
2 bad Effects of RBC Sickling
• Chronic hemolysis
• Microvascular occlusion with resultant tissue
hypoxia and infarction
– Correlates with the number of irreversibly sickled cells
Chronic hemolysis in SS anemia
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
– “Cytoplasmic maturation defect”
In Thalessemias: Severity of hematologic manifestations is directly
related to _________
the degree of chain imbalance
– 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
