L16- RBC Pathology II (Thalassemia, PNH)

Question 1

Thalassemia Syndromes:

• (1) describe the type of RBCs (chromic, cytic status)
• (2) describe the process of RBC damage

-most common is (3) populations because of (4)

Answer 1

1- hypochromic, microcytic RBCs due to low [Hb]
2- excess of unimpaired normal chains (α/β chain) –> aggregations –> insoluble inclusions –> EXTRAvascular hemolysis

3- Mediterranean, African, Asian regions
4- protects against P. Falciparum Malaria

Question 2

describe the 2 types of β-thalassemia / gene mutations: include β-chain levels and location of mutations in β-gene

Answer 2

β+: reduced β-chains synthesis b/c promoter region mutations

β0: no β-chain production b/c mutations cause inappropriate splicing or chain termination (nonsense mutation)

Question 3

list the 3 types of β-thalassemia clinical syndromes: include name, possible gene makeup, anemia severity

Answer 3

β-thalassemia major:

• β0/β0, β+β+, β+β0
• severe (transfusion dependent) anemia

β-thalassemia minor/trait:

• β+/β, β0/β
• mild asymptomatic anemia

β-thalassemia intermedia:

• variable gene combinations :β+/β0, β+/β+, β0/β, β+β (all combinations of the minor/major syndromes)
• moderately severe anemia (no regular transfusions needed)

Question 4

β-thalassemia major features start to appear (1) age and presents with Hb levels of (2). The reduced β-globin synthesis impairs Hb production and leads to (3) type of anemia. The relative excess of α-globin chains will result in (4).

Answer 4

1- 6-9 mos (once HbF dec)
2- 3-6 g/dL
3- hypochromic microcytic anemia
4- precipitation –> aggregations –> membrane damage –> dec RBC survival rate

Question 5

list the clinicopathological features of β-thalassemia major as a direct result from α-chain aggregation causing decreased RBC survival causing…. (hint- 4)

Answer 5

1) ineffective erythropoiesis, 75% of precursors die in hyperplastic bone marrow
2) hematopoietic marrow expansion => prominent facial bones, bony cortex erosion + new bone formation

3) splenomegaly, hepatomegaly via extravascular hemolysis and extramedullary hematopoiesis
4) excess dietary Fe absorption + regular blood transfusions => Fe overload (hemosiderosis OR secondary form) affecting heart, liver, skin, pancreas

Question 6

Diagnosis of β-thalassemia major:

• (1) non-lab findings
• (2) blood findings
• (3) special tests

Answer 6

1- clinical findings, FHx

2- CBC for anemia, hemolysis evidence, Peripheral blood findings: microcytic hypochromic anemia, anisopoikilocytosis, polychromatic cells +/- nucleus

3- Hb electrophoresis

Question 7

describe the results of a positive Hb electrophoresis for β-thalassemia major

Answer 7

• HbA reduced or absent
• HbA2 normal or increased
• HbF increase, may become the predominant Hb

Question 8

β-thalassemia minor:

• (1) symptoms
• (2) peripheral blood findings
• (3) Hb electrophoresis findings
• (4) why is it important to recognize β-thalassemia trait

Answer 8

1- asymptomatic

2- mild hypochromic microcytic anemia +/- erythrocytosis and normal RDW

3- reduced HbA, inc HbA2, normal/inc HbF

4- i) avoid treating as Fe deficient anemia, ii) genetic counseling

Question 9

In β-thalassemia major, (1) and (2) are the major complications. (3) maybe given orally for complication prevention, and (4) maybe a potentially curative procedure.

Answer 9

1- growth retardation and death w/o regular blood transfusions
2- cardiac failure: severe anemia (high output failure) OR Fe overload => cardiomyopathy

3- Fe chelators, prevent overload
4- bone marrow transplant

Question 10

describe the 4 types of α-thalassemia by genetic make-up

Answer 10

1) α-thalassemia minima / silent carrier: 1 α-gene deleted; (α/α, α/-)
2) α-thalassemia minor / trait: 2 α-gene deleted; (α/α, -/-) Asians, (α/-, α/-) Africans [only Asian variety can => severe form offspring]
3) hemoglobin H disease: 3 α-genes deleted; (α/-, -/-)
4) hemoglobin Barts disease (hydrops fetalis): all 4 α-genes deleted; (-/-, -/-)

Question 11

what are the signs and symptoms in α-thalassemia minima

Answer 11

(silent carrier, 1 α-gene deletion)

• asymptomatic
• no anemia, no microcytic RBCs

Question 12

what are the signs and symptoms in α-thalassemia minor/trait

Answer 12

(2 α-gene deletion)

• asymptomatic
• mild hypochromic microcytic anemia

Question 13

what are the signs and symptoms in hemoglobin H disease

Answer 13

(3 α-gene deletion)
-HbA, HbH both produced

• HbH forms from excess β-chains forming tetramers
• HbH has high O2 affinity => severe tissue hypoxia (won’t release O2 to tissues)
• HbH prone to oxidation => inclusions in older RBCs –> extravascular hemolysis –> moderate anemia

(typically transfusion dependent)

Question 14

what are the signs and symptoms in hemoglobin barts

Answer 14

(all 4 α-gene deletion)
-incompatible with life —- Hydrops Fetalis

• HbF can’t form –> excess γ-chains form tetramers => Hb Barts
• Bart bodies have high O2 affinity –> no O2 delivery to tissues => death w/o intrauterine transfusions
• Fetus: pale, edematous, hepatomegaly, splenomegaly (Hydrops Fetalis)

Question 15

PNH = (1):

-(common/rare) (hereditary/acquired) disorder due to mutation in (4) gene found on (5) chromosome (‘single hit’)

Answer 15

1- paroxysmal nocturnal hemoglobinuria
2/3- rare, acquired genetic defect
4- PIGA (phosphatidylinositol glycan class-A) gene
5- X-linked

Question 16

_____ is the only hemolytic anemia caused by acquired genetic defect

Answer 16

PNH- paroxysmal nocturnal hemoglobinuria

Question 17

PIGA proteins:

• involved in synthesis of (1)
• (1) is responsible for (2)
• defective (2) leaves people susceptible to (3)

Answer 17

1- GPI, glycosylphosphatidylinositol

2- glycolipid links dozens of cell surface proteins to hematopoietic cells (bloog group Ags, adhesion molecules, complement regulatory proteins)

3- complement attack, even with low levels of complement

Question 18

PNH:

• (1) are the GPI linked proteins that regulate complement activity
• (2) is the result of absent (1) proteins
• (3) is why it is worse at night

Answer 18

1- decay accelerating factor (CD55), membrane inhibitor of reactive lysis (CD59), C8 binding protein

2- inc susceptibility of RBCs for lysis or injury via complement (INTRAvascular hemolysis)

3- dec blood pH during sleep => inc complement activity

Question 19

list the clinical features of PNH

Answer 19

• Anemia –> fatigue, dyspnea
• hemoglobinuria => chronically leads to renal insufficiency
• Pancytopenia / Aplastic anemia –>
  i) platelet dysfunction –> prothrombotic state –> inc bleeding risk (main cause of death)
  ii) dec WBC –> infection risk

Question 20

list the signs (via lab tests) that may indicate a suspected PNH

Answer 20

• hemolytic anemia w/ neg. coombs test
• aplastic anemia
• refractory anemia
• unexplained thrombosis in conjunction with cytopenia / hemolysis

Question 21

Lab finding for PNH:

• CBC checks for (1)
• intravascular hemolysis evidence includes (2)
• (3) older screening tests
• (4) current gold standard test

Answer 21

1- anemia, pancytopenia
2- hemoglobinuria, hemosiderinuria
3- sucrose hemolysis test, Ham’s acid hemolysis test

4- Flow Cytometry including FLAER: shows absent CD55, CD59 on RBCs
(FLAER = FLuorescent AERolysin, an inactive toxin derived from bacteria that binds GPI)

Question 22

list the 4 common complications of PNH

Answer 22

1) thrombosis: 40% develop venous thrombosis
2) aplastic anemia
3) Fe deficiency: due to hemosiderinuria
4) AML / MDS (acute myeloid leukemia and myelodysplastic syndrome) in 5-10% of Pts

Question 23

what is the Tx for PNH

Answer 23

• immunosuppression: specific inhibitors of complement –> very expensive therapy
• bone marrow transplant