sickle cell anemia (hemoglobinopathies) by: jessica hebert, rob mcelroy, beth mcquinn, yuway tsing,...
TRANSCRIPT
Sickle Cell Anemia (Hemoglobinopathies)
By: Jessica Hebert, Rob McElroy, Beth McQuinn, Yuway Tsing, Elias Kass, Bill Walter,
Amelia Kramer
What are hemolytic anemias?
• Decreased life-span of erythrocytes
• Removal of RBCs may be:– Intravascular (within the
blood)– Extravascular (within the
spleen)
• Associated with:– Increased erythropoiesis– Increased hemoglobin
catabolism byproducts
Possibilities?
• Many types of hemolytic anemias:– G6PD-Deficiency– Hemoglobinopathies
• Sickle Cell Disease• Hereditary Spherocytosis• Thalassemias
– Immunohemolysis– Others…
•http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Search&db=books&doptcmdl=GenBookHL&term=sickle+cell+prevalence+AND+hstat%5Bbook%5D+AND+340265%5Buid%5D&rid=hstat6.section.17004
Population Prevalence
African American 1/375 HbSS , 1/835 HbSC , 1/10 HbSA (trait)
American > 50,000 (2 mil with sickle cell trait)
Mediterranean descent significant
Caribbean descent Not significant
East Indian Ancestry Not significant
Arabian Not significant
Latin American 1/1000-1400
Greeks Not significant
Italians Not significant
Background:Prevalence in Populations
Clinical Presentation: Signs and Symptoms
General anemia pallor, fatigue, SOB on exertion
Acute chest syndrome cough, dyspnea, chest pain, fever
Infection malaise, cough and chest pain, diarrhea and/or vomiting
Painful crises persistent pain in skeleton, chest, and/or abdomen
Hand-foot syndrome swollen and painful hands and feet (by 2 years of age: 50% of Jamaican and 25% of American children with sickle cell anemia have experienced at least one episode of dactylitis)
Stroke (affects 10% of patients; 6-17% of children and young adults), sudden neurologic deficits including motor, difficulty with language, writing, and/or reading; seizures; sensory deficits; altered consciousness
Priapism penile erection not related to arousal
Delayed growth and puberty
Patient more slender or small in size.
Jaundice Yellowing of skin and eyes
Other Some people remain asymptomatic into late childhood and are only incidentally diagnosed
http://www.ornl.gov/sci/techresources/Human_Genome/posters/chromosome/sca.shtml
Background
• There are a range of Treatments per extremes or per symptoms
Clinical Presentation
Sickle Cell Anemia
A hereditary genetic disorder that results in the production of abnormal hemoglobins
In Sickle Cell, the Beta chain is affected by a point mutation…
Source: Robbins
One small point mutation leads to a major problem
when HbS is deoxygenated…
Deoxyhemoglobin A (HbA)
http://www.ornl.gov/sci/techresources/Human_Genome/posters/chromosome/hbb.shtml
Deoxyhemoglobin S (HbS)
A prolonged environment of low oxygen leads to aggregation and polymerization of hemoglobins into long chains of rod-like fibers, causing the RBC to form the shape of a crescent or sickle.
http://www.humanillnesses.com/original/images/hdc_0001_0003_0_img0235.jpg
• Donut-shaped• Soft and malleable• Able to pass through
small spaces• Lifespan ~120 days
• Sickle-shaped• Hard and rod-like• Gets stuck in narrow
spaces• Lifespan ~20 days
Sickling of red blood cells leads to:
1. Vaso-occlusive complications
2. Severe anemia
3. Chronic hyperbilirubinemia
Vaso-occlusive complications
Occur in areas with:
• Prolonged, low oxygen tension
• Decreased pH
• Inflammation
• Low blood flow
Source: Robbins
Severe Anemia and Chronic
Hyperbilirubinemia 1. Young RBCs with HbS can
alternate between the sickled and normal formation.
2. However, sickling causes oxidative damage to the RBCs cell membrane (and to the cells around it).
3. Eventually, RBCs become irreversibly sickled.
Severe Anemia and Chronic Hyperbilirubinemia
• Irreversibly sickled cells end up in the spleen.
• Hemolysis occurs at the splenic cords.
• Decreased RBCs and increased bilirubin
• Infarction and fibrosis causes autosplenectomy.
Source: Robbins
G6PD-Deficiency Distribution
G6PD-Deficiency Distribution
• 12% of males of African descent (A type)
• 22% of Southeast Asian males (Mahedian type)
• 50% of Kurdish males (Mediterranean type)
• Also, a significant prevalence in males of Italian, Greek, Lebanese, Iraqi, and Sephardic heritage (Mediterranean type)
G6PD-DeficiencyPresenting Symptoms
• Fatigue or muscle weakness
• Jaundice or pallor• Dyspnea• Dark urine• Pain (especially
abdominal)• Splenomegaly
Glucose 6-Phosphate
G6PD-Deficiency – Pathology
• Genetic abnormalities (of which there are several varieties) lead to deficient or impaired enzyme function
• High levels of oxidants (from foods, drugs, exercise, infections) may damage or denature proteins within the erythrocyte
• RBCs may then be subject to intravascular or extravascular hemolysis
G6PD Crisis Precipitation - Beans
• Broad beans (favism)– Fava beans, bell beans, fever beans, hava
beans, pigeon beans, horse beans, tick beans, silkworm beans, English dwarf beans
G6PD Crisis Precipitation - Oxidizing Drugs
– Antimalarials (primaquine, quinine, quinidine)
– NSAIDs (aspirin, ibuprofen)
– Antibiotics (sulfonamides)
– Nitrofurantoin– TCM herbs (rhizoma
coptidis, margarita, calculus bovis)
Other oxidants– Henna – primarily infants and pregnant
women– Naphthlene (moth balls) – regular exposure
Early Lab Tests – CBC
• RBC – Low
• Hct – Low
• Hb – Low
• MCV – Normal to High
• MCHC – Low to Normal
• MCH – Low to Normal
• So…initial CBC is only your starting point
Early Lab Tests – Urinalysis
• Hemoglobin– Elevated post-crisis
• Bilirubin– Elevated post-crisis
• Urobilinogen– Elevated post-crisis
• May also see hematuria, proteinuria, LDH• These account for dark color of urine following a
crisis, but are also non-specific for any given type of hemolytic anemia
Early Lab Tests - Smear
• Often readily seen with initial CBC, or easily ordered alongside
• If anemias are suspected, probably best to run a smear in the early stages
• G6PD-Deficiency may show:– Heinz bodies
• Denatured Hb bound to cell membrane• May damage cell membrane, leading to intravascular hemolysis
– “Bite” cells• Spleen removes portion of RBC that had Heinz body, preventing
intravascular hemolysis
– These aren’t typically present immediately following an acute hemolytic crisis (problem cells have been destroyed)
Other Non-Specific Lab Tests
• Reticulocyte count– May be elevated following acute crisis (6-8 weeks)– May be normal in non-crisis situations– May be reduced in aplastic crisis (could go to zero)– Should be considered in conjunction with smear, other data
• Serum bilirubin– Present in the unconjugated (prehepatic) form– Elevated after an acute hemolytic crisis
• Serum haptoglobin– Binds to Hb in the blood for removal by spleen (preventing Hb
from excretion in the urine, which could lead to renal failure)– Decreased (depleted) after an acute hemolytic crisis
Screening for G6PD
• Cells from G6PD-deficient subjects can’t convert the oxidized substrate to a reduced state
• Different tests use different substrates
• Substrates can either be the enzyme’s natural substrate (NADP) or substrates from secondary reactions
Fluorescent Screening Test
• G6PD generates NADPH
• NADPH fluoresces under long-wave UV light
• No G6PD? No fluorescence.
Fluorescent Screening Test
• Shortcomings:– False Negative: young red blood cells have more
G6PD activity. During an acute hemolytic episode, reticulocytosis results in a bigger population of young red blood cells, so even in G6PD Deficiency, the fluorescence may appear normal.
– False Positive: if the patient is anemic, very little fluorescence may be seen because there are very few red blood cells.
Methemoglobin Reduction Test
• Sodium nitrite converts Hb (hemoglobin) to Hi (methemoglobin)
• Adding methylene blue should stimulate the pentose phosphate pathway, reducing methemoglobin
• In G6PD Deficiency, methemoglobin persists
Methemoglobin Reduction Test
• Normal blood → clear red color
• Deficient blood → brown color
• Heterozygotes → intermediate color
Methemoglobin Reduction Test
- Takes longer than fluorescence
+ Extremely inexpensive
+ Requires only a water bath
• Test should be complemented by cytochemical analysis
Cytochemical Analysis
• Only way to reliably detect deficiency in heterozygous women
• More reliable than assay
• Good complement for other tests
Cytochemical Analysis
• Treat red cells to convert their oxyhemoglobin (HbO2) to methemoglobin (Hi)
• In the presence of G6PD, Hi converts back to HbO2• Add MTT, which will be reduced by HbO2 to an insoluble
form• In G6PD Deficiency:
– Hi persists– MTT is not reduced– Ergo, cells are not stained
Cytochemical Analysis
Cytochemical Analysis
• Interpretation:– Normal G6PD activity: majority stained– Hemizygous: majority unstained– Heterozygotes:
• Most show mosaicism (40-60% unstained)• Some have only 2-3% unstained (fortunate
lyonization)
G6PD Assay
• Tracks activity of enzyme by following rate of production of NADPH over time
• NADPH has peak of UV light absorption at 340nm
• Note potentially misleading results in following table
G6PD Assay
Male Gd+ (n orm al) Gd-
(e nti rely defici e nt )
Fem a le Gd+/ Gd+ ( norm al) Gd-/ Gd-
(e nti rely defici e nt )
Gd+/ Gd- ( so me what deficie nt)
In he a lth 7 -1 0 <2 2 -7
In in creas e d de mo ly s is un relate d t o G6P D defi ci en c y
15 4 4 -9
Dur in g rec o ve ry f ro m G6P D- re lat e d an e m ia
6.5 ( appe ar s
norm al) 6 -1 0 ( appe ars
norm al)
Values are examples only (Lewis 10e, p226)
G6PD Assay
• Interpretation:– Red cells are likely to lyse from G6PD deficiency if
they have less than ~20% of normal enzyme activity
• Confounding factors:– With reticulocytosis, the relatively large population of
reticulocytes yields a higher enzyme activity, covering up deficiency
– Therefore, a low-normal enzyme activity assay during reticulocytosis points towards G6PD deficiency (without deficiency, values would be very high during reticulocytosis)
– Re-evaluate after reticulocytosis slows
Choosing Appropriate Tests
• More than one test should be used• Are they in the middle of a hemolytic crisis?
– Anemia + Reticulocytosis = Misleading results
• For females, cytochemical analysis should be used
• Normal and deficient control blood should always be used for comparison– Sheep are naturally deficient, bah!