Microspherocytic anemia. Enzymopathies

HEMOLYTIC ANEMIAS

Premature destruction of erythrocytes (Er)
↑reticulocyte count, BR, LDH. ↓serum haptoglobin
Divided into intrinsic (inherited) and extrinsic (acquired)
4 types of intrinsic haemolytic anemias
- Structural haemoglobinopathies – sickle cell disease synthesis of a structurally abnormal Hb protein
- Thalassemias – quantitative abnormality (decreased synthesis) of a globin chain
- Enzyme defects – G6PD-D, PK-D
- Membrane defects – hereditary spherocytosis

2. HEREDITARY SPHEROCYTOSIS (HS)

RBC Membrane

3 main components
- Phospholipid (PL) bilayer
- Integral membrane proteins and glycoprotein – embedded in the PL bilayer
  - Important transmembrane proteins – band 3 protein and glycophorin
- Cytoskeleton scaffold – gives RBC its shape. Mainly composed of spectrin. Ankyrin binds spectrin to band 3 protein

Epidemiology

Pathophysiology

Defective vertical attachment between PL bilayer and the cytoskeleton scaffold
Results from mutations in the gene for ankyrin
Defective vertical attachment causes loss of PLs from the cell membrane
Surface area of RBC decreases and cell assumes shape of a sphere
Spherocytes are less flexible than normal RBCs and get trapped and destroyed in the spleen
Intrinsic defect with extravascular hemolysis
Increased permeability to Na⁺ and K⁺ means the pump is constantly running, which causes additional metabolic stress
- Cells have an increased requirement for glucose

Clinical features

Highly variable
Neonatal hyperbilirubinemia
Older patients have mild/mod anaemia with hyperbilirubinemia and mild splenomegaly
Bilirubin gallstones
Pts can have exacerbations of anaemia associated with infections

Diagnosis

MCV is normal/low. Increase MCHC – specific for this haemolytic anaemia
Blood smear shows microspherocytes
↑reticulocyte count
DAT should be done to exclude immune haemolytic anaemia
Osmotic fragility test – classic test for HS
- Er incubated in saline solutions with osmolality ranging from normal to pure water
- Percent hemolysis is measured by spectrophotometer
- Er from HS patients hemolyse at higher saline concentration than normal cells

Treatment

3. ENZYME DEFECTS

Glucose-6-Phosphate Dehydrogenase Deficiency (G6PD-D)

Epidemiology

Pathophysiology

First enzyme in hexose monophosphate shunt, which is required to generate NADPH, which is needed for regeneration of glutathione by glutathione reductase
In absence of sufficient glutathione, Hb is oxidised and precipitates in the cells (Heinz bodies) – results in hemolysis
Aggregates of oxidised Hb are removed from the cell by the spleen, resulting in bite cells
Level of G6PD is highest in reticulocytes and lower in aged cells
- In normal people the activity of the enzyme remains enough to protect older cells from oxidative stress
Normal G6PD half life is 62 days
- In the common African variant of G6PD deficiency half life is 13 days

Clinical features

Most patients are not anaemic and have no hemolysis at baseline state
African variant is Class III – episodes of hemolysis are precipated by infection, oxidative drugs, chemicals, surgery
Episodes of hemolysis are indicated by sudden onset jaundice, pallor, dark urine, abdominal pain
Mediterranean variant (class II) is MC in Caucasians
- Uncooked fava beans are common cause of hemolysis in these patients
Class I variants are very unstable
- Anemia and jaundice noted in neonates

Diagnosis

Treatment

Pyruvate kinase deficiency (AR)

Epidemiology

Pathophysiology

Defect in Emden-Meyerhof pathway
Er with PK deficiency generate less ATP and NADH from glucose
2,3-BPG accumulates in RBCs
- Since ↑2,3-BPG facilities oxygen unloading, patients tolerate anaemia well and are asymptomatic despite ↓Hb ( Right shift of Hb-O₂ dissociation curve >> ↑release of O₂ to tissues)
Decreased ATP leads to cellular dehydration and formation of echinocytes

Clinical features

Diagnosis

Treatment