SM_247b: Congenital Hemolytic Anemias

Question 1

Hemoglobin has ___ subunits including ___ and ___

Answer 1

Hemoglobin has 4 subunits including 2 alpha globin chains and 2 beta globin chains

Question 2

In reduced state, heme is covalently bound to ___ and ___

Answer 2

In reduced state, heme is covalently bound to O2 and CO

Question 3

____ and ____ direct production of hemoglobin during development

Answer 3

Beta locus on chromosome 11 and alpha locus on chromosome 16 direct production of hemoglobin during development

Question 4

Describe hemoglobin switching

Answer 4

Hemoglobin switching

• Switch from epsilon to gamma completed by 10 weeks gestational age
• Embryonic Hb (Zeta2-epsilon2) is replaced by fetal Hb (alpha2-gamma2) which predominates at birth

Question 5

Describe distribution of functional hemoglobin by 6 months of age

Answer 5

Distribution of functional hemoglobin by 6 months of age

• 90-97% HbA (alpha2-beta2): normal adult Hb
• 1% HbF (alpha2-gamma2): fetal Hb
• 2% HbA2 (alpha2-delta2): variant adult Hb

Question 6

Mutations in Hb affect ____, ____, or ____

Answer 6

Mutations in Hb affect solubility, oxygen affinity, or synthesis

• Beta mutations more common than alpha mutations
• Genetic basis characterized by point mutations, nucleotide insertions / deletions, crossovers

Question 7

Describe clinically important structural Hb mutants

Answer 7

Clinically important structural Hb mutants

• Sickle cell phenotypes
• Thalassemia phenotypes
• Unstable hemoglobins
• Abnormal oxygen affinity

Question 8

Sickle cell mutation is an example of a ____

Answer 8

Sickle cell mutation is an example of a balanced polymorphism

• Heterozygous state confers protection from malarial infection
• Homozygous state confers risk of premature death

Question 9

Sickle cell disease is caused by a ___

Answer 9

Sickle cell disease is caused by a substitution in the 6th codon of the beta gene

• Glutamic acid replaced by valine
• Mutant beta globin chain
• Sickle hemoglobin

Question 10

Describe common genotypes of sickle cell disease

Answer 10

Common genotypes of sickle cell disease

• Homozygous / compound heterozygous: Hb SS, Hb SC, Hb S / beta0 or beta+ thalassemia
• Heterozygous state: Hb C or beta thalassemia trait is clinically insignificant, Hb S trait is associated with medical complications in adult

Question 11

____ is the primary event in the pathogenesis of sickle cell disease

Answer 11

Intracellular polymerization of HbS during deoxygenation is the primary event in the pathogenesis of sickle cell disease

Question 12

Describe sickle Hb polymerization

Answer 12

Sickle Hb polymerization depends on

• HbS concentration: direct correlation exists between gelation and HbS concentration
• Oxygenation status: polymerization occurs only in deoxygenated state
• pH concentration: solubility of deoxygenated HbS is lowest between 6.0 and 7.2
• HbF and other non-sickle Hb concentration: HbF, HbA, HbA2 have inhibitory effect on sickle polymerization
• Cation homeostasis / hydration: activated KCl co-transport increases intracellular Hb concentration and polymer formation

Question 13

____ and ____ are involved in sickle cell dehydration

Answer 13

Gardos channel and KCl co-transporter are involved in sickle cell dehydration

Question 14

In vivo sickling leads to ____ and ____

Answer 14

In vivo sickling leads to hemolysis and vaso-occlusion

• Hemolysis: leads to shortened RBC life span, anemia, and vasomotor dysregulation
• Vaso-occlusion: leads to pain, disability, and end organ damage

Question 15

Describe vaso-occlusion in sickle cell disease

Answer 15

Vaso-occlusion in sickle cell disease

• Inflammation, genetic modifiers, hypercoagulability, cell adhesion, oxidative stress, RBC sickling, endothelial dysfunction, inflammation

Question 16

Adherent ___ interact with sickled RBCs

Answer 16

Adherent leukocytes interact with sickled RBCs

Question 17

Describe diagnosis of sickle cell disease in newborn period

Answer 17

Diagnosis of sickle cell disease in newborn period

• On newborn screening
• Lack of symptoms at birth explained by protective effect of fetal Hb

Question 18

Describe the diagnosis of sickle cell disease in an older child

Answer 18

Diagnosis of sickle cell disease in an older child

• Typical peripheral blood smear
• Predominance of sickle Hb on electrophoresis
• Laboratory findings: variable anemia, reticulocytosis, and hyperbilirubinemia

Question 19

Describe clinical spectrum of sickle cell disease

Answer 19

Clinical spectrum of sickle cell disease

Question 20

___ episodes represent the hallmark of sickle cell disease

Answer 20

Vaso-occlusive (pain) pisodes represent the hallmark of sickle cell disease

• Hand-foot syndrome / dactylitis early in childhood
• Triggers of pain episodes may vary
• Episodes commonly involve lower back, chest, knees, and long bones
• Pain may be difficult to differentiate from bone or joint infection

Question 21

___ is the most common cause of death in children with sickle cell disease

Answer 21

Infection is the most common cause of death in children with sickle cell disease

• High risk with encapsulated organisms: S. pneumoniae, H. influenzae, S. aureus, Salmonella spp.
• Functional asplenia
• May trigger complications such as aplastic crisis

Question 22

Children with sickle cell disease are at greatest risk for infection due to ___

Answer 22

Children with sickle cell disease are at greatest risk for infection due to encapsulated organisms

• S. pneumoniae, H. influenzae, S. aureus, Salmonella spp.

Question 23

Acute chest syndrome is ___

Answer 23

Acute chest syndrome is fever + abnormal CXR + any respiratory symptom

• Etiology is multifactorial: infection, pulmonary infarction, fat emboli
• Pain episode is the most common preceding event

Question 24

Overt ___ may occur in patients with sickle cell disease

Answer 24

Overt stroke may occur in patients with sickle cell disease

• Affected area is usually in the distribution of large vessels
• Aplastic crisis, acute chest, low O2 are risk factors

Question 25

Mainstays of treatment for sickle cell disease are ____ and \_\_\_\_

Answer 25

Mainstays of treatment for sickle cell disease are preventive measures and therapeutic intervention

Question 26

Crizalizumab is a ___ used to treat sickle cell disease

Answer 26

Crizalizumab is a selectin inhibitor used to treat sickle cell disease

Question 27

Voxelator is a ___ used to treat sickle cell disease

Answer 27

Voxelator is a hemoglobin allosteric modulator used to treat sickle cell disease

Question 28

L-gutamine is an ___ used to treat sickle cell disease

Answer 28

L-gutamine is an antioxidant used to treat sickle cell disease

Question 29

RBC membrane is composed of ____ and \_\_\_\_

Answer 29

RBC membrane is composed of a fluid lipid bilayer and a network of skeletal and transmembrane proteins * Membrane functions to maintain RBC structural integrity, provide strength and flexibility, import iron / electrolytes / water, removes metabolic waste

Question 30

Describe lipid bilayer of RBCS

Answer 30

Lipid bilayer of RBCs * Comprises 50% of RBC membrane * Composed of free cholesterol and phospholipids * Organized into planar bilayer * Inherent symmetry present = flip-flop * Disorganization explained by bilayer coupling theory

Question 31

RBCs with expanded outer layer are \_\_\_\_

Answer 31

RBCs with expanded outer layer are echinocytes

Question 32

RBCs with expanded inner layer are \_\_\_\_

Answer 32

RBCs with expanded inner layer are stomatocytes

Question 33

Describe membrane proteins of RBCs

Answer 33

RBC membrane proteins * Classified by: electrophoretic mobility (SDS-polyacrylamide), function (membrane skeleton), location (integral vs peripheral) * Integral (traverse lipid bilayer): band 3 * Peirpheral (interact at membrane surface only): spectrin, ankyrin

Question 34

Ankyrin has a ____ and is \_\_\_\_

Answer 34

Ankyrin has a wide cellular distribution and is the primary link between spectrin and band 3 (peripheral protein)

Question 35

Spectrin involves ___ and ___ subunits, self-associates into \_\_\_, and functions to ___ and \_\_\_

Answer 35

Spectrin involves alpha and beta subunits, self-associates into heterotramers, and functions to support lipid bilayer and regulate mobility of integral proteins (peripheral protein)

Question 36

Band 3 plays a critical role in ___ and binds \_\_\_

Answer 36

Band 3 plays a critical role in Cl-/HCO3- exchange and binds cytoplasmic membrane components (integral)

Question 37

Describe disruption of the RBC membrane

Answer 37

Disruption of the RBC membrane

Question 38

Determinants of intact RBC membrane are \_\_\_\_, \_\_\_\_, and \_\_\_\_

Answer 38

Determinants of intact RBC membrane are cell surface / volume ratio (most important), structural integrity, and deformability

Question 39

RBC surface loss results in \_\_\_\_, leading to \_\_\_\_, \_\_\_\_, \_\_\_\_, and \_\_\_\_

Answer 39

RBC surface loss results in membrane fragmentation, leading to spherocytes, poikilocytes, bite cells, and elliptocytes

Question 40

RBC volume gain results in \_\_\_\_, leading to \_\_\_\_

Answer 40

RBC volume gain results in increased membrane permeability, leading to stomatocytes

Question 41

RBC surface gain results in \_\_\_\_, leading to \_\_\_\_

Answer 41

RBC surface gain results in accretion of membrane lipid, leading to target cells

Question 42

RBC volume loss results in ____ and \_\_\_\_, leading to \_\_\_\_

Answer 42

RBC volume loss results in decreased Hb and increased membrane permeability, leading to target cells

Question 43

Describe hereditary spherocytosis

Answer 43

Hereditary spherocytosis * Most common inherited hemolytic anemia * Deficiency in membrane proteins leads to mechanical instability, membrane loss, and spheroid fragile RBCs * Autosomal dominant inheritance most of hte time * Ankyrin \> spectrin \> band 3 deficiency

Question 44

Describe the pathophysiology of hereditary spherocytosis

Answer 44

Pathophysiology of hereditary spherocytosis 1. Spectrin / ankyrin deficient areas -\> unsupported membrane OR band 3 deficient membrane -\> clustered llpids 2. Budding off of membrane 3. Spherocytosis 4. Increased splenci trapping 5. Erythrostasis 6. Hemolysis

Question 45

Describe clinical features of hereditary spherocytosis

Answer 45

Clinical features of hereditary spherocytosis * Positive family history * Neonatal hyperbilirubinemia * Varied phenotypic severity * Evidence of hemolysis: anemia, jaundice, reticulocytosis * Complications: gallstones, aplastic crisis (parvovirus), splenomegaly

Question 46

Describe diagnosis and treatment of hereditary spherocytosis

Answer 46

Diagnosis and treatment of hereditary spherocytosis * Peripheral smear * Lab features: variable anemia, reticulocytosis, elevated MCHC, elevated total bilirubin * Osmotic fragility test * Genetic testing * Treatment: supportive therapy, transfusions, and splenectomy

Question 47

Describe hereditary elliptocytosis

Answer 47

Hereditary elliptocytosis * Autosomal dominant * Causedby alpha or beta spectrin deficiency * Clinical heterogeneity: carrier state, severe form (hereditary pyropoikilocytosis)

Question 48

Describe Southeast Asian ovalocytosis

Answer 48

Southeast Asian ovalocytosis * Autosomal dominant * Caused by band 3 deficiency * Mild anemia despite marked RBC rigidity

Question 49

Pentose phosphate pathway generates \_\_\_\_

Answer 49

Pentose phosphate pathway generates reducing power (NADPH) against oxidative stress * Glucose-6-phosphate dehydrogenase plays a major role

Question 50

\_\_\_ plays a major role in the pentose phosphate pathway

Answer 50

Glucose-6-phosphate dehydrogenase plays a major role in the pentose phosphate pathway

Question 51

Glycolysis (Embden-Meyerhof pathway) generates \_\_\_\_

Answer 51

Glycolysis (Embden-Meyerhof pathway) generates high-energy phosphates for ATP * Pyruvate kinase is major rate limiting enzyme

Question 52

\_\_\_\_ is major rate limiting enzyme in glycolysis (Embden-Meyerhof pathway)

Answer 52

Pyruvate kinase is major rate limiting enzyme in glycolysis (Embden-Meyerhof pathway)

Question 53

Describe the pentose phosphate pathway

Answer 53

Pentose phosphate pathway 1. Generation of reducing power 2. Regeneration of reduced form of glutathione 3. Reduction of oxygen radicals

Question 54

Describe glycolysis (Embden-Meyerhof pathway)

Answer 54

Glycolysis (Embden-Meyerhof pathway)

Question 55

Describe RBC enzymopathies

Answer 55

RBC enzymopathies * Associated with phenotypic variability * Lack of characteristic RBC changes at baseline * Causes chronic non-spherocytic hemolytic anemia * Degree of hemolysis dependent on importance of enzyme and residual function of variant enzyme

Question 56

Gd is located \_\_\_\_

Answer 56

Gd is located on long arm of X chromosome * Deficient expression in hemizyous males * Variable expression in heterozygous females

Question 57

G6PD enzyme is present in \_\_\_\_, \_\_\_\_, and activity is ____ and \_\_\_\_

Answer 57

G6PD enzyme is present in all cells, cannot be replaced in RBCs, and activity is age-dependent and higher in reticulocytes

Question 58

Structural changes in G6PD due to mutations affect ____ and \_\_\_\_

Answer 58

Structural changes in G6PD due to mutations affect catalytic function and in vivo stability

Question 59

In G6PD deficient RBCs, exogenous factors cause \_\_\_, \_\_\_, and \_\_\_

Answer 59

In G6PD deficient RBCs, exogenous factors cause decreased NADPH, decreased reduced form glutathione, and decreased protection from oxidative stress

Question 60

\_\_\_\_, \_\_\_\_, and ____ are triggers of acute hemolytic anemia in G6PD deficiency

Answer 60

Medications, infection, and fava beans / other legumes are triggers of acute hemolytic anemia in G6PD deficiency

Question 61

Describe symptoms of acute hemolytic anemia due to G6PD deficiency

Answer 61

Symptoms of acute hemolytic anemia due to G6PD deficiency * Hemolysis * Fever * Abdominal nd back pain * Coca-cola urine * Jandice and pallor * Hepatosplenomegaly * Hypovolemic shock

Question 62

Describe lab findings of G6PD deficiency

Answer 62

G6PD deficiency lab findings * Normocytic anemia * Brisk reticulocytosis * Leukocytosis * Hyperbilirubinemia * Hemoglobinuria * Renal insufficiency * Low RBC G6PD deficiency

Question 63

Describe glycolytic enzymopathies

Answer 63

Glycolytic enzymopathies * Deficiencies in multiple enzymes in pathway * Grouped as CNSHA * Autosomal recessive inheritance * Normal peripheral smear * Normal osmotic fragility * Partial response to splenectomy * Diagnose by quantitative assays

Question 64

Pyruvate kinase deficiency has ___ inheritance and ___ mutations are most common

Answer 64

Pyruvate kinase deficiency has autosomal recessive inheritance and PKLR mutations are most common * Impairment in substrate kinetics, regulatory properties, and thermal stability

Question 65

Pyruvate kinase is important for ___ formation

Answer 65

Pyruvate kinase is important for ATP formation * Deficiency results in increased cation permeability, increased 2,3-DPG, and rightward shift of HbO2 dissociation curve

Question 66

Pyruvate kinase deficiency presents with \_\_\_, \_\_\_, \_\_\_, \_\_\_, and \_\_\_

Answer 66

Pyruvate kinase deficiency presents with anemia, jaundice, splenomegaly, gallstones, and leg ulcers * Hyperbilirubinemia common in newborns

Question 67

Describe deficiencies of the Embden-Meyerhof pathway

Answer 67

Deficiencies of the Embden-Meyerhof pathway * Autosomal dominant usually * Various degrees of non-spherocytic hemolytic anemia * Important enzyme deficiences: hexokinase, aldolase, glucose-6-phosphate isomerase, triosephosphate isomerase, phosphoglycerate kinase