Flashcards in Session 5- Haemolytic Anaemia And Haemoglobinopathies Deck (49):
What is the physiological life cycle of a red blood cell?
Red blood cells are produced in the bone marrow by erythropoiesis and haemoglobin synthesis also occurs here. Then peripheral red blood cells mature and develop function/structure and metabolism. Red blood cells are then removed by the reticulocytes- endothelial system.
What two types of anaemia may result from mutations in the genes that encode the globin proteins?
Thalassaemia and sickle cell diseases.
What is thalassaemia?
Reduced rate of synthesis of normal alpha or normal beta globin chains (thalassaemia can either be alpha or beta).
What is sickle cell disease?
Synthesis of an abnormal haemoglobin.
Why is there a low level of intracellular haemoglobin in thalassaemia?
The red cells are hypochromic (little haemoglobin) and microcytic (smaller).
What is the silent carrier state of alpha thalassaemia?
It is a deletion of a single alpha globin gene therefore it is asymptomatic, without anaemia.
What is the alpha thalassaemia trait?
This is the deletion of two alpha globin genes, it may affect both genes on one chromosome or one gene of each chromosome. There is minimal or no anaemia and no physical signs.
Microcytosis and hypochromia.
What is Haemoglobin H (HbH) disease?
This is the deletion of three alpha globin genes, leads to tetramers of B globin called HbH being formed. Moderately sever anaemia- microcytic, hypochromic anaemia with target cells and Heinz bodies in the blood film.
What are Heinz bodies?
Inclusions within red blood cells which are composed of denatured haemoglobin.
What is it called when all four alpha globin genes are deleted?
Hydrophobic getalis, excess of gamma globin chains form tetramers (Hb Bart) that are unable to deliver oxygen to the tissues, it results in death of embryo.
How does haemolytic anaemia arise?
It results from the abnormal breakdown (haemolysis) of red blood cells in blood vessels (intravascular haemolysis) or the spleen (Extravascular haemolysis).
Bone marrow can compensate for any decrease in lifespan resulting from haemolysis by increasing production so why does haemolytic anaemia occur?
Well if the average lifespan/breakdown of an erythrocyte reduces to a certain extent then increased production by the bone marrow is unable to compensate and anaemia will therefore occur.
What are the symptoms caused by haemolytic anaemia?
Shortness of breath/fatigue/ accumulation of bilirubin (Substance released when haemaglobin is broken down) leads to jaundice and gall stones (the conjugated bilirubin blocks the gall bladder ducts in the form of gall stones).
What can haemolytic anaemias be classified by?
Either inherited or acquired...
Acquired (damage to cells) can be caused by...
- Mechanical damage
- Antibody damage
- Oxidant damage
- Heat damage (burns)
- Enzymatic damage
Inherited (Defective gene)
- Glycolysis defect
Pyruvate kinase deficiency limits ATP production
Penthouse P pathway- g6pdh deficiency (GSH can not be regenerated)
What is MAHA?
Microangipathic haemolytic anaemias are a group of acquired haemolytic anaemias where red cells are damaged by physical trauma.
What does the trauma in microangiopathic haemolytic anaemia normally come from?
Red cells getting snagged as they try to pas through small vessels which are laden with fibrin stands in situations where there is an increased activation of the coagulation cascade.
Disseminated intravascular coagulation (DIC)- a condition where clotting and bleeding occur at the same time.
Thrombocytopenia purpurin- a syndrome where small thrombi form within the microvasculature.
HAEMOLYTIC uraemia Syndome (HUS)- seen more commonly in children after developing E. coli diarrhoea.
RBC also damaged by the shear stress produced by a defective heart valve ie: Aortic valve stenosis.
What are immune haemolytic anaemias Caused by?
They result from infections, lymphoproliferative disorders and reactions to drugs.
What are the two classifications of immune haemolytic anaemias?
You have: Warm or Cold haemolytic anaemias.
In warm haemolytic anaemias IgG antibodies recognise epitomes on the red cell membrane leading to macrophages in the spleen recognising the antibody coated red cells and either disposing of the whole cell by phagocytosis or nibbling a bit off. In the latter case, since some membrane is lost the red cell tends. To round up forming a Spherocyte.
What happens in cold autoimmune haemolytic anaemia?
IgM autoantibodie recognise the red cell epitomes and there is also complement fixed to the patient red cells. The IgM autoantibodies bind best at cooler temps, they tend to bind to the red cells in more distal parts of the body ie: fingertips.
Pyruvate kinase deficiency is an example of inherited haemolytic anaemias, explain what it is.
PKLR gene encodes for two out of four pyruvate isoenzymes (The two isoenzymes it encodes four are expressed in the liver and erythrocytes respectively) therefore mutations in the PKLR gene lead to a deficiency in pyruvate kinase. Pyruvate kinase catalyses the final step of glycolysis where pyruvate is produced, therefore if deficient this step cannot occur and ATP cannot be produced, red blood cells lack mitochondria therefore this was there only source of ATP. The red cells lose K+ to plasma and then shrink due to water moving down its concentration gradient and out of cells.
G6PDH deficiency is another inherited haemolytic anaemia, what is this?
G6PDH deficiency is Glucose-6-phosphate dehydrogenase deficiency, it is an X linked recessive inborn error of metabolism. G6PDH i the rate limiting enzyme of the penthouse phosphate pathway which supplies NADPH (Reducing energy), NADPH is required to protect against oxidative stress by maintaining the levels of reduced glutathione- GSH. The penthouse pathway is the only source of reduced glutathione in red blood cells which are particularly affected by defects in the glucose-6-phosphate dehydrogenase enzyme, therefore patients with G6PDH deficiency are at risk of haemolytic anaemia in states of oxidative stress ie: infection/exposure to chemicals or medication.
How can oxidative stress (infection/drugs/broad beans) lead to Haemolysis?
Cause lipid peroxidation which results in cell membrane damage and the lack of deformity leads to mechanical stress.
Causes protein damage- aggregates of cross linked haemoglobin- HEINZ BODIES.
What should you do before starting your patients on drug with a known risk of haemolysis?
Check for G6PDH deficiency, as then won’t be able to protect against oxidative damage which causes haemolysis.
What is hereditary Spherocytosis?
An inherited autosomal dominant disease resulting in abnormalities in erythrocyte membrane proteins which impeded the ability of the cell to change shape, mutations in the genes coding for 4 different proteins have been shown to cause the disease.
What are the 4 different proteins in which the genes are subject to mutations which cause hereditary Spherocytosis?
SPECTRIN- an actin crosslinking and molecular scaffold protein which links the plasma membrane to the actin cytoskeleton.
ANKYRIN- the integral membrane proteins to the underlying SPECTRIN- actin cytoskeleton)
Band 3 (facilitates chloride and bicarbonate exchange across the plasma membrane and is also involved in a physical linkage of the plasma membrane to the underlying cytoskeleton.
Protein 4.2- An ATP binding protein which may regulate the association of protein 3 with ANKYRIN.
How is a spherocyte shape to the red blood cell formed?
Mutation of the gene coding for these proteins results in a local disconnection of the cytoskeletal and membrane. Followed by vesiculatio now the unsupported membrane components leads to a progressive reduction in the membrane surface area and hence a spherocyte shape.
What does the poor deformability of spherocytes mean?
That they become trapped and damaged as they pas through the spleen (Extravascular haemolysis) resulting in reduction in the lifespan of erythrocytes and haemolytic anaemia. The deficit in cell deformability of spherocytes only appears to be a problem in the spleen rather than the small capillaries since the red cells return to a nearly normal lifespan following splenectomy.
Patients with mild symptoms due to Spherocytosis do not normally require treatment but what is the treatment for those with severe symptoms?
Partial or full splenectomy improves the anaemia, the spherocytes still remain but are no longer listed by spleen.
What are haemoglobinopathies and what are the two main categories?
Inherited disorders where expression of one or more of the globin chains of haemoglobin is abnormal.
Two main categories:
Abnormal haemoglobin variants: Result from mutations in the genes for alpha or beta globin chains which alter the stability and function of haemoglobin.
Thalassaemias: Reduced or absent expression of normal alpha or beta globin chains, leads to a reduced level of haemoglobin rather than the presence of an abnormal haemoglobin.
What are Myeloproliferative neoplasms?
Group of diseases of the bone marrow in which excess cells are produced, they arise from genetic mutations in the precursors of the myeloid lineage in the bone marrow.
What are the four main types of MPN (myeloproliferative neoplasms)?
Polychythaemia vera (Excess erythrocytes)
Essential thrombocytopenia (overproduction of megakaryocytes leading to excess platelets)
Primary myelofibrosis (proliferative phase followed by replacement of haematopoietic tissue by connective tissue leading to impairment of the generation of all blood cells (pancytopenia).
Chronic myeloid leukaemia (Excess granulocytes).
What is polycythaemia?
A disease state in which the volume percent of erythrocytes in the blood (the haematocrit) exceeds 52% of males or 48% of females. Arises from increase in number of erythrocytes (absolute polycythaemia) or a decrease in the plasma volume (Relative polycythaemia).
Absolute polycythaemia can either be secondary or primary, what is meant by this?
Primary- the abnormality originates in the bone marrow ie: polycythaemia Vera.
Secondary- increased levels of erythropoietin, which is either abnormal production or a physiological response to hypoxia.
What is thrombocytosis?
An increase in the platelet count compared to normal range of a person of same gender/age. It can result from myeloproliferative neoplasm. Where the thrombocytosis is generally referred to as essential thrombocythaemia.
What is essential thrombocythaemia?
The increase in number of platelets (Thrombocytosis) due to a myeloproliferative neoplasm.
What is What is essential thrombocythaemia (blood cancer) characterised by?
The over production of platelets by megakaryocytes in the bone marrow. Over half caused by JAK2 mutations and some caused by thrombopoietin receptor resulting in disease.
What are the common symptoms of essential thrombocythaemia?
Numbness in extremetities
Burning pain in hands/feet (Erythromelalgia).
What are patients with thrombocythaemia treated with?
Patients with low risk for blood clotting are treated with aspirin.
High risk patients are given hydroxycarbamide to reduce platelet count.
What is thrombocytopenia?
An abnormally low level of platelets, can either be inherited/acquired.
What is acquired thrombocytopenia?
Detected from a full blood count, patients experience bleeding gums/nosebleeds/ heavier menstrual periods/ petechia (small/red purple spots on skin) can result as a decrease in platelet production/consumption of platelets or an increased destruction of platelets.
What is immune thrombocytopenia purpura?
An autoimmune disease characterised by isolated thrombocytopenia(low platelet levels) which can take an acute (Short lived) or chronic course.
What is ITP normally due to?
Decreased platelet production ie: liver failure/ folate or B12 deficiency/leukaemia/sepsis
Increased platelet consumption ie: thrombotic thrombocytopenic purpura/haemorrhage
Increased platelet destruction ie: autoimmune/drug induced/ hypersplenism,
What is the treatment of ITP?
Corticosteroids/ immunosuppressive drugs/ IV pooled human immunoglobulin, splenectomy and thrombopoietin receptor agonists.
What is primary myelofibrosis?
A myeloproliferative neoplasm where the proliferation of mutated hematopoietic stem cells results in reactive bone marrow fibrosis which eventually leads to the replacement of marrow with scar tissue (Collagen deposition). Mobilisation of mutated progenitor cells. From bone marrow can also occur and these cells can colonise liver and spleen leading to extramedullary haemopoiesis. Patients with myeloproliferative neoplasm usually show an enlarged liver and spleen. Mutations in the JAK2 gene are often associated with the disease
What are the symptoms of primary myelofibrosis?
What are the treatment options for primary myelofibrosis?
Treatment options are largely supportive/generally unsatisfactory. Hydroxycarbamid/folic acid and allopurinol may have some benefits and patients with advance disease may require blood transfusions and sometimes splenectomy. The drug ruxolitinib is an inhibitor of JAK2 and has been shown to significantly reduce spleen volume and improve symptoms of myelofibrosis.
What is the difference between acute and chronic leukaemia?
Acute rapidly causes bone marrow failure due to large numbers of immature blast cells overwhelming the ability of the tissue to produce mature blood cells while chronic leukaemia are often slow to cause symptoms and may even be picked up as a chance finding on a blood count, in chronic there is often differentiation.
What is chronic myeloid leukaemia?
Unregulated growth of myeloid cells in the bone marrow which leads to the accumulation of mature granulocytes (mainly neutrophils) as well as myelocytes in the blood. Associated with spec chromosomal translocation called Philadelphia chromosome (Reciprocal translocation between chromosomes 9 and 22).