Sickle cell anemiaDr. Rohini C Sane

SICKLE CELL ANAEMIA-SICKLE CELL HAEMOGLOBIN

• 1957-first sickle cell hemoglobin (Hb S )

• FIRST MOLECULAR DISEASE ONE GENE ONE PROTEIN( Beadle & Taum )

Crescent shape ( low hemoglobin content )

Occurrence of sickle cell anemia

• Tropical area –black population25% population Heterozygous ,central part of & east part of India (scheduled tribe =ST)

MOLECULAR BASIS OF SICKLE CELL ANAEMIA

Linus Pauling ( 1954 Noble prize ) reported abnormal electrophoretic mobility & peptide mapping

Glutamic acid ( sixth position on beta globin chain ) replaced by Valine (Recessive Mutation )Hb A & Hb F PREVENT SICKLING

Sickle cell disease1. Glutamic acid Valine (HbS )—hydrophilic to hydrophobic amino

acid

2. Stickiness on surface of a Hb molecule

3. polymerization of Hb in RBC Distortion of RBC into sickle shaped

4. Deoxy HbS –protrusion on one side and cavity on other side

5. Many molecule adhere together

6. Deletion of HbS temp & pH dependent

7. Solubility is minimal at pH 6.35

8. Solubility increases with increase in pH

Sickle cell disease

Sickle cell disease

• solubility is minimum at pH 6.35

• solubility increases with increase in pH

• decrease in oxygen saturation & Hb concentration

• increase in proportion of polymeric & soluble molecules

Sickle cell disease

• HbS bind & transport oxygen

• Decrease in oxygen saturation & Hb concentration relative proportion of polymeric & soluble molecules

• Deoxygenated state sickling viscosity of blood increases slows down the circulation decrease in oxygen tension- further sickling

• Vicious cycle

DE OXYGENATED STATE

SICKLING

VISCOCITY OF BLOOD INCREASES

SLOWS DOWN CIRCULATION

OXYGEN TENSION DECREASES

FURTHER SICKLING

DE OXYGENATED STATE

SICKLING

VISCOCITY OF BLOOD

INCREASES

SLOWS DOWN CIRCULATION

OXYGEN TENSION DECREASES

FURTHER SICKLING

Viscous cycle of sickling

Mechanism of sickling in sickle cell anemia

• Glutamic acid replaced by Valine on beta chain at sixth position

• Decrease in solubility of HbS (Deoxy HbS )—T form

• Solubility of HbS ( OXY Hb S ) unaffected

• HbA lack sticky patches

• Formation of long aggregates of Deoxy HbS polymerization of HbS –(Deoxy ) fibrous PPT Stiff fibers distorts RBC (SICKLE ) LYSIS

• Sickle cells plug capillaries occlusion of major vessels infarction of organ ( spleen ) death occurs in second decade of life

Formation of long aggregates of Deoxy HbS

Sticky patches of one HbS ( Deoxy Hb)+ receptors of another HbS ( DEOXY ) AGGREGATE

polymerization of HbS –(Deoxy )

Fibrous precipitate

Stiff fibres distorts RBC ( SICKLE )

Lysis

Sickle cell

Plug in capillaries

Occlusion of major vessels

Interaction in organ (spleen )

Death occurs in second decade of life

HbS gives protection against plasmodium falciparum causative of malaria

• Normal RBC (malaria parasite enters) multiplies RBC lysishemolytic anemia

• RBC with sickle cell trait malarial parasite enters could not multiply no malaria, no RBC lysis normal health

1. Shorter life span of RBC carrying HbS interrupts parasite cycle

Malaria parasite increase in acidity( decrease in pH )increase in sickling RBC to 40% (normal 2% ) lysis of RBC

2. Low potassium level in sickled cells unfavorable for parasite

sickle cell trait is an adaptation for survival of individual in malarial infested region

Life span of sickle cell (homozygous )< 20yrs

Sickle cell anemia

Homozygous1.Two mutant genes (one from each

parent)that code for beta chain

2.RBCs contain HbS

3.Sickle cell disease

4.Life span < 20years

Heterozygous1 .one gene of beta chain is affected other gene

normal

2.RBCs contain Hbs & HbA

3.Sickle cell trait

4.Normal life –no clinical symptoms

Abnormalities associated with HbS

1. Life long hemolytic anemia-RBC fragile continuous hemolysis

2.Tissue damage & pain sickle cells block capillaries poor bloodsupply to tissue extensive damage inflammation pain

3.Increased susceptibility to infection

4. Premature Death -Homozygous life span < 20yrs

Diagnostic of sickle cell anemia

1.Sickling test: blood smear + reducing agent ( sodium dithionite )microscopic examination

Normal individual- sickle cells < 2% , sickle cell patient - sickle cell > 2%

2.solubility test : hem lysate in presence of reducing agent opalescence in hemolysate (presence of Deoxy HbS )

3. ELECTROPHORESIS OF Hb:

Glutamic acid (- ve charged ) Valine ( neutral ) decreased mobility towards anode

4. Finger printing technique –Ingram

5.Sourthen blot

Management of sickle cell disease 1.Repeated blood transfusions iron overload ( Iron chelater Des ferroxamine )

cirrhosis

2.Treatment ( anti sickling agents )

a) Urea

b) *Cyanates (0.1 N) increase affinity for oxygen toHbS Decrease Deoxy HbS

c) Aspirin

• INTERFERE WITH POLYMRIZATION inhibit sickling

3. sodium butyrate : induce HbF production CLINICAL IMPROVEMENT

4.Gene therapy

5.Family counselling

*side effects of cyanates nerve damage

25% HbA ,50 % heterozygous Hb AS SA ,25%Homozygous

Inheritance of Hb variants

AA SA SC 25% 25% 25% DOUBLE 25% HETEROZYGOTE

HETEROZYGOTE