SM_247b: Congenital Hemolytic Anemias Flashcards
Hemoglobin has ___ subunits including ___ and ___
Hemoglobin has 4 subunits including 2 alpha globin chains and 2 beta globin chains
In reduced state, heme is covalently bound to ___ and ___
In reduced state, heme is covalently bound to O2 and CO
____ and ____ direct production of hemoglobin during development
Beta locus on chromosome 11 and alpha locus on chromosome 16 direct production of hemoglobin during development
Describe hemoglobin switching
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
Describe distribution of functional hemoglobin by 6 months of age
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
Mutations in Hb affect ____, ____, or ____
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
Describe clinically important structural Hb mutants
Clinically important structural Hb mutants
- Sickle cell phenotypes
- Thalassemia phenotypes
- Unstable hemoglobins
- Abnormal oxygen affinity
Sickle cell mutation is an example of a ____
Sickle cell mutation is an example of a balanced polymorphism
- Heterozygous state confers protection from malarial infection
- Homozygous state confers risk of premature death
Sickle cell disease is caused by a ___
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
Describe common genotypes of sickle cell disease
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
____ is the primary event in the pathogenesis of sickle cell disease
Intracellular polymerization of HbS during deoxygenation is the primary event in the pathogenesis of sickle cell disease
Describe sickle Hb polymerization
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
____ and ____ are involved in sickle cell dehydration
Gardos channel and KCl co-transporter are involved in sickle cell dehydration
In vivo sickling leads to ____ and ____
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
Describe vaso-occlusion in sickle cell disease
Vaso-occlusion in sickle cell disease
- Inflammation, genetic modifiers, hypercoagulability, cell adhesion, oxidative stress, RBC sickling, endothelial dysfunction, inflammation
Adherent ___ interact with sickled RBCs
Adherent leukocytes interact with sickled RBCs
Describe diagnosis of sickle cell disease in newborn period
Diagnosis of sickle cell disease in newborn period
- On newborn screening
- Lack of symptoms at birth explained by protective effect of fetal Hb
Describe the diagnosis of sickle cell disease in an older child
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
Describe clinical spectrum of sickle cell disease
Clinical spectrum of sickle cell disease
___ episodes represent the hallmark of sickle cell disease
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
___ is the most common cause of death in children with sickle cell disease
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
Children with sickle cell disease are at greatest risk for infection due to ___
Children with sickle cell disease are at greatest risk for infection due to encapsulated organisms
- S. pneumoniae, H. influenzae, S. aureus, Salmonella spp.
Acute chest syndrome is ___
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
Overt ___ may occur in patients with sickle cell disease
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
Mainstays of treatment for sickle cell disease are ____ and ____
Mainstays of treatment for sickle cell disease are preventive measures and therapeutic intervention
Crizalizumab is a ___ used to treat sickle cell disease
Crizalizumab is a selectin inhibitor used to treat sickle cell disease
Voxelator is a ___ used to treat sickle cell disease
Voxelator is a hemoglobin allosteric modulator used to treat sickle cell disease
L-gutamine is an ___ used to treat sickle cell disease
L-gutamine is an antioxidant used to treat sickle cell disease
RBC membrane is composed of ____ and ____
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
Describe lipid bilayer of RBCS
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
RBCs with expanded outer layer are ____
RBCs with expanded outer layer are echinocytes
RBCs with expanded inner layer are ____
RBCs with expanded inner layer are stomatocytes
Describe membrane proteins of RBCs
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
Ankyrin has a ____ and is ____
Ankyrin has a wide cellular distribution and is the primary link between spectrin and band 3
(peripheral protein)
Spectrin involves ___ and ___ subunits, self-associates into ___, and functions to ___ and ___
Spectrin involves alpha and beta subunits, self-associates into heterotramers, and functions to support lipid bilayer and regulate mobility of integral proteins
(peripheral protein)
Band 3 plays a critical role in ___ and binds ___
Band 3 plays a critical role in Cl-/HCO3- exchange and binds cytoplasmic membrane components
(integral)
Describe disruption of the RBC membrane
Disruption of the RBC membrane
Determinants of intact RBC membrane are ____, ____, and ____
Determinants of intact RBC membrane are cell surface / volume ratio (most important), structural integrity, and deformability
RBC surface loss results in ____, leading to ____, ____, ____, and ____
RBC surface loss results in membrane fragmentation, leading to spherocytes, poikilocytes, bite cells, and elliptocytes
RBC volume gain results in ____, leading to ____
RBC volume gain results in increased membrane permeability, leading to stomatocytes
RBC surface gain results in ____, leading to ____
RBC surface gain results in accretion of membrane lipid, leading to target cells
RBC volume loss results in ____ and ____, leading to ____
RBC volume loss results in decreased Hb and increased membrane permeability, leading to target cells
Describe hereditary spherocytosis
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
Describe the pathophysiology of hereditary spherocytosis
Pathophysiology of hereditary spherocytosis
- Spectrin / ankyrin deficient areas -> unsupported membrane OR band 3 deficient membrane -> clustered llpids
- Budding off of membrane
- Spherocytosis
- Increased splenci trapping
- Erythrostasis
- Hemolysis
Describe clinical features of hereditary spherocytosis
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
Describe diagnosis and treatment of hereditary spherocytosis
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
Describe hereditary elliptocytosis
Hereditary elliptocytosis
- Autosomal dominant
- Causedby alpha or beta spectrin deficiency
- Clinical heterogeneity: carrier state, severe form (hereditary pyropoikilocytosis)
Describe Southeast Asian ovalocytosis
Southeast Asian ovalocytosis
- Autosomal dominant
- Caused by band 3 deficiency
- Mild anemia despite marked RBC rigidity
Pentose phosphate pathway generates ____
Pentose phosphate pathway generates reducing power (NADPH) against oxidative stress
- Glucose-6-phosphate dehydrogenase plays a major role
___ plays a major role in the pentose phosphate pathway
Glucose-6-phosphate dehydrogenase plays a major role in the pentose phosphate pathway
Glycolysis (Embden-Meyerhof pathway) generates ____
Glycolysis (Embden-Meyerhof pathway) generates high-energy phosphates for ATP
- Pyruvate kinase is major rate limiting enzyme
____ is major rate limiting enzyme in glycolysis (Embden-Meyerhof pathway)
Pyruvate kinase is major rate limiting enzyme in glycolysis (Embden-Meyerhof pathway)
Describe the pentose phosphate pathway
Pentose phosphate pathway
- Generation of reducing power
- Regeneration of reduced form of glutathione
- Reduction of oxygen radicals
Describe glycolysis (Embden-Meyerhof pathway)
Glycolysis (Embden-Meyerhof pathway)
Describe RBC enzymopathies
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
Gd is located ____
Gd is located on long arm of X chromosome
- Deficient expression in hemizyous males
- Variable expression in heterozygous females
G6PD enzyme is present in ____, ____, and activity is ____ and ____
G6PD enzyme is present in all cells, cannot be replaced in RBCs, and activity is age-dependent and higher in reticulocytes
Structural changes in G6PD due to mutations affect ____ and ____
Structural changes in G6PD due to mutations affect catalytic function and in vivo stability
In G6PD deficient RBCs, exogenous factors cause ___, ___, and ___
In G6PD deficient RBCs, exogenous factors cause decreased NADPH, decreased reduced form glutathione, and decreased protection from oxidative stress
____, ____, and ____ are triggers of acute hemolytic anemia in G6PD deficiency
Medications, infection, and fava beans / other legumes are triggers of acute hemolytic anemia in G6PD deficiency
Describe symptoms of acute hemolytic anemia due to G6PD deficiency
Symptoms of acute hemolytic anemia due to G6PD deficiency
- Hemolysis
- Fever
- Abdominal nd back pain
- Coca-cola urine
- Jandice and pallor
- Hepatosplenomegaly
- Hypovolemic shock
Describe lab findings of G6PD deficiency
G6PD deficiency lab findings
- Normocytic anemia
- Brisk reticulocytosis
- Leukocytosis
- Hyperbilirubinemia
- Hemoglobinuria
- Renal insufficiency
- Low RBC G6PD deficiency
Describe glycolytic enzymopathies
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
Pyruvate kinase deficiency has ___ inheritance and ___ mutations are most common
Pyruvate kinase deficiency has autosomal recessive inheritance and PKLR mutations are most common
- Impairment in substrate kinetics, regulatory properties, and thermal stability
Pyruvate kinase is important for ___ formation
Pyruvate kinase is important for ATP formation
- Deficiency results in increased cation permeability, increased 2,3-DPG, and rightward shift of HbO2 dissociation curve
Pyruvate kinase deficiency presents with ___, ___, ___, ___, and ___
Pyruvate kinase deficiency presents with anemia, jaundice, splenomegaly, gallstones, and leg ulcers
- Hyperbilirubinemia common in newborns
Describe deficiencies of the Embden-Meyerhof pathway
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
