Haemoglobinopathies Dr. Saly Rashad

Objectives: Upon completion of this lecture, students should be able to: To understand the normal structure and function of haemoglobin To understand how the globin components of haemoglobin change during development, and postnatally. To understand the mechanisms by which the thalassaemias arise. To appreciate the clinical presentations and complications of thalassaemia To appreciate the contribution of haemolysis and ineffective erythropoiesis to the pathophysiology of thalassaemia

To understand the pathophysiology of sickle cell anaemia. To be able to describe the clinical presentation and complications of sickle cell anaemia. To understand the role of haemoglobin electrophoresis and high performance liquid chromatography in the investigation of globin disorders. To appreciate the many other haemoglobin variants associated with disease

Introduction: Different haemoglobins are synthesized in the embryo, fetus and adult. They all have a structure made up of two different pairs of globin chains, each attached to one heme molecule.

Normal adult blood contains three types of haemoglobin

Globin synthesis Globin genes are located in Chromosome 11(β) and 16 (α). Hb switching is physiological process . Occurs 3–6 months after birth when synthesis of the γ chain is replaced by β chains, the haemoglobin is changed from fetal to adult type.

Haemoglobin Abnormalities Hb abnormalities result from the following:- Synthesis of an abnormal haemoglobin (Qualitative). HbS, HbC, HbD & HbE. Reduced rate of synthesis of normal α‐ or β‐globin chains (Quantitative) α‐ and β‐thalassaemias.

Thalassaemia: These are a heterogeneous group of genetic disorders that result from a reduced or absent of synthesis of α or β chains. α‐Thalassaemias are caused by defective synthesis of α chain. β‐Thalassaemias are caused by defective synthesis of ß chain β‐Thalassaemia is more common in the Mediterranean region while α‐thalassaemia is more common in the Far East. Most thalassaemias are inherited an autosomal recessive fashion.

Clinically: Clinically thalassaemias classified according their severity into:- Thalassaemia major, severe and transfusion dependent Thalassaemia intermedia,with a moderate degree of anaemia and splenomegaly , non‐transfusion dependent thalas­saemia. Thalassaemia minor, usually due to a carrier state for α‐ or β‐thalassaemia (Symptomless).

Beta thalassaemia: Are the most important types of thalassaemia. There are two copies of β globin chains per cell on chromosome 11. If the abnormality involve one gene (heterozygous)→ β-thalassaemia minor. If the abnormality involves two genes (homozygous)→β-thalassaemia major or intermedia.

β‐Thalassaemia major (Cooley anaemia) Patients have abnormalities of both β globin genes. Pathogenesis: Mutation may involve any step in globin chain production Excess α chains precipitate in erythroblasts and in mature red cells causing severe ineffective erythropoiesis and haemolysis.

Clinical features: Symptoms develop at about 3–6 months after birth when the switch from γ‐ to β‐chain production (Decline of HbF). Severe anaemia (pallor, dyspnea… ) Stunted growth (failure to thrive) Manifestation of haemolysis (jaundice, stones in liver) Enlargement of the liver and spleen (extramedullary haemopoiesis) Thalassaemic facies : tendency to fractures and bossing of the skull with a ‘hair‐on‐end’ appearance on X‐ray).

The facial appearance of a child with β‐thalassaemia major The facial appearance of a child with β‐thalassaemia major. The skull is bossed with prominent frontal and parietal bones; the maxilla is enlarged. Skull X‐ray in β‐thalassaemia major. There is a ‘hair on‐end’ appearance

Infections → due to transfusion (HCV, HBV, HIV) or following splenectomy (Pneumococcal, Haemophilus and meningococcal infections). Repeated blood transfusions and iron overload which leads to organ damage(heart, liver & endocrine). Osteoporosis.

Laboratory diagnosis Anaemia: (3-9g/dL)the anaemia is a severe hypochromic, microcytic. Anisopokilocytosis Target cells ↑ reticulocytes, normoblasts(NRBC) and basophilic stippling in the blood film. ↑ bilirubin. Hb electrophoresisabsence of Hb A, with almost all the circulating haemo­ globin being Hb F.

β-Thalassaemia trait (minor) It is usually more sever than α-trait. Hb may be ↓ but is not usually <10.0g/dL. HbA2 (2α 2δ)↑.

Alpha Thalassemia: Caused by α‐globin gene deletions or less frequently mutations. Pathogenesis: α thalassemia is due to impaired production of α globin chains, which leads to a relative excess of gamma(γ) globin chains in the fetus and newborn, and beta (β) globin chains in children and adults.

Variants of α-Thalassaemia: α-Thalassaemia trait-2 /Silent carrier Deletion of single α-gene Absence of RBC abnormality Thalassaemia trait-1 Deletion of 2 α-genes Asymptomatic, minimal or no anaemia Hb H disease Deletion of 3 α-genes Severe anaemia Hydrops fetalis Deletion of all α-genes

Sickle cell diseases: Sickle cell disease is an inherited chronic haemolytic anaemia Inheritance is autosomal recessive. Genetic: substitution of valine for glutamic acid at position 6 of the β- globin chain Homozygous (HbSS)= sickle cell anaemia. Heterozygous (Hb AS)= sickle cell trait. 2-May-19

Sickle cell anaemia: Pathogenesis: Hb S when deoxygenated, causing RBCs to sickle. Sickle cells are fragile , and haemolyse. Initial sickling is reversible with administration of oxygen, but recurrent sickling causes irreversible sickling due to membrane damage.

Hb SS( sickle cell anaemia) Clinical features: Highly variable. Many have few symptoms while others have severe and frequent crises. The clinical features are of a severe haemolytic anaemia with episodes of crises. Vaso - occlusive crises: Most frequent type. Caused by occlusion of the blood capillaries with distal ischemia and infarction. Crises may be precipitated by infections, cold, exercise ,dehydration, acidosis, deoxygenation. May cause:

Hand-foot’ syndrome (painful dactylitis caused by infarcts of the small bones) is frequently the first presentation of the disease Bone→ osteomyleitis, avasular necrosis. Brain→convulsions, stroke Retina→ hemorrage Chest→acute chest syndrome, with cough, fever and chest pain. CVS→pulmonary HTN. Abdomen: acute abdomenal pain, gall stones Renal→papilary necrosis, enuresis, haematourea Skin chronic leg ulcer is common in old age > 7 yrs

Sequestration crises: Common in children. Large amounts of blood become sequestrated in spleen and liver →sudden increase in the size of liver and spleen and circulatory collapse. Serious condition usually need exchange transfusion or splenectomy.

Aplastic crises Haemolytic crises Occur as a result of infection with parvovirus or from folate deficiency. Characterized by a sudden ↓ in hae­moglobin and↓ reticulocytes, Usually requiring transfusion. Haemolytic crises Characterized by an increased rate of haemolysis and ↓ in haemoglobin but ↑ in reticulocytes .

Laboratory findings: ↓ Hb (6-9 g/dl),↑Retics (10-20%),↑bilirubin BF: marked poikilocytosis with sickle cells, nucleated red ells and target cells, basophilic stippling, Howell-Joly bodies. Screening tests for sickling are positive when the blood is deoxygenated (e.g. with dithionate) HPLC or Hb electrophoresis: Hb SS: 80-90 %, no HbA, Hb F (5-15%).

(a) Sickle cell anaemia: peripheral blood film showing deeply staining sickle cells, target cells and polychromasia.

Sickle cell trait (Hb AS): Asymptomatic carriers have one abnormal gene and one normal gene . Benign condition with no anaemia and no abnormal clinical features.

Reference: 5/2/2019