There are numerous fragmented RBCs seen here. Some of the irregular shapes appearas "helmet" cells. Such fragmented RBCs are known as "schistocytes" and they areindicative of a microangiopathic hemolytic anemia (MAHA) or other cause forintravascular hemolysis. This finding is typical for disseminated intravascularcoagulopathy (DIC).
• Inheritance – AD (75%) – Compound heterozygosity• Northern Europe (1 in 5000)• Defective cell membrane skeleton• Spherical & less deformable RBC• Splenic sequestration % destruction
Pathogenesis• Cytoskeletal defect• The life span of the affected red cells 10 to 20 days
Hereditary Spherocytosis• Spectrin – Major protein of membrane cytoskeleton• Two polypeptide chains – α and β• Spectrin is tethered to the inner surface of cell membrane by ankyrin, protein 4.2 to trans membrane transporter band 3
Hereditary Spherocytosis• Gene mutation involving ankyrin, protein 4.2, spectrin or band 3 reduce membrane stability• Spontaneous loss of cell membrane• ↓ Cell surface to volume ratio – spheroidal shape• Spherocytes are less deformable and vulnerable to splenic sequestration and destruction
Schematic representation of the red cell membrane cytoskeleton and alterations leading to spherocytosis and hemolysis
The size of many of these RBCs is quite small, with lack of the central zone of pallor.These RBCs are spherocytes. In hereditary spherocytosis, there is a lack of spectrin, akey RBC cytoskeletal membrane protein. This produces membrane instability thatforces the cell to the smallest volume--a sphere. In the laboratory, this is shown byincreased osmotic fragility. The spherocytes do not survive as long as normal RBCs.
Hereditary Spherocytosis• Osmotic fragility test – Confirmatory test• Spherocytes are vulnerable to osmotic lysis induced in vitro by hypotonic salt solution• Hemolysis starts at 0.8 gm% and completes between 0.5 – 0.4 gm%
G6PD - deficiency• X – linked disorder• More than 350 G6PD genetic variants are recognised• G6PD A- – 10% of American black – Normal enzyme activity in reticulocyte – Unstable enzyme – half time 13 days (62 days)• G6PD Mediterranean – Severe ↓ enzyme activity – less than 10% – Severe hemolysis
G6PD - deficiency• Asymptomatic• Infectious disease / drug exposure• Sudden onset of anemia• Hemoglobinuria, Hemoglobinemia• Abdominal / low back pain• Self limited
G6PD - deficiency• PBS – Spherocytes, erythrocyte fragments, bite cells, Heinz bodies, polychromasia• Measurement of enzyme activity – Fluorescent spot test – Dye reduction test
Acquired Membrane disorder• Paroxysmal nocturnal hemoglobinuria (PNH) is a disease that results from acquired mutations in the phosphatidylinositol glycan complementation group A gene (PIGA), an enzyme that is essential for the synthesis of certain cell surface proteins
Attachment of proteins to cell membrane• Transmembrane proteins• GPI linked proteins: The others are attached to the cell membrane through a covalent linkage to a specialized phospholipid called glycosylphosphatidylinositol (GPI).• In PNH, these GPI-linked proteins are deficient because of somatic mutations that inactivate PIGA
• PNH blood cells are deficient in three GPI-linked proteins that regulate complement activity: 1. decay–accelerating factor, or CD55 2. Membrane inhibitor of reactive lysis, or CD59 3. C8 binding protein.• Of these factors, the most important is CD59, a potent inhibitor of C3 convertase that prevents the spontaneous activation of the alternative complement pathway.
• Red cells, platelets, and granulocytes deficient in these GPI-linked factors are abnormally susceptible to lysis or injury by complement• In red cells this manifests as intravascular hemolysis• The hemolysis is paroxysmal and nocturnal