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Presentation on theme: "GENETIC DISORDER OF HAEMOGLOBIN"— Presentation transcript:

Haemoglobinopathies and Thalassaemias

2 Haemoglobin A conjugated protein consisting of iron-containing heme and protein (globin) Globin chains are of different types: -chains and non  -chains Each molecule is a tetramer of two - and non  chains. Each globin binds a haem in a haem binding site. Haemoglobin binds and transports oxygen from lungs to the tissues, while it transports CO2 from tissues to the lungs.


4 Types of Hemoglobin in adults
Globin genes Gene product Tetramers Name of Conc. in Chromosome (globin) in RBCs haemoglobin adult 11   , -chain 2  Hb A  , -chain 2 2 Hb A   ,-chain 2  Hb F <1.0

5 Structure of each Globin gene
Chromosome 11 G A  5’ 3’ Chromosome 16  2 1 2 1 5’ 3’ Structure of each Globin gene 5’ 3’ Exon 1 Intron 1 Exon 2 Intron 2 Exon 3

6 Hemoglobin synthesis α α γ δ β α α γ δ β Chromosome 16 Chromosome 11
25% 25% 0.5% 1.5% 48% α α γ δ β α α γ δ β 25% 25% 0.5% 1.5% 48% Chromosome 16 Chromosome 11

7 Hemoglobinopathy; definition
An inherited mutation of the globin genes leading to a qualitative or quantitative abnormality of globin synthesis.

8 Structural hemoglobinopathy
Amino acid substitution in the globin chain e.g. sickle hemoglobin (HbS)

9 The Thalassemias Syndromes in which the rate of synthesis of a globin chain is reduced:- beta thalassemia – reduced beta chain synthesis alpha thalassemia – reduced alpha chain synthesis

10 Disorders of Haemoglobin
Thalassaemias (Biosynthetic disorder of Hb) Co-existing structural / biosynthetic disorders Haemoglobinopathies (Structural disorder of Hb) Constitute a major health problem in several populations of the world (particularly those residing in malaria endemic region)

11 Haemoglobinopathies Genetic structural disorder.
Due to mutation in the globin gene of haemoglobin. Mostly autosomal recessive inheritance. Result in haemoglobin variants with altered structure and function. Altered functions include: Reduced solubility Reduced stability Altered oxygen affinity- increased or decreased Methaemoglobin formation

12 Hemoglobinopathies Decrease, lack of, or abnormal globin
May be severe hemolytic anemia Abnormal Hb with low functionality Mutation may be deletion, substitution, elongation Hb electrophoresis may be helpful

13 Types of Mutations in Haemoglobin
Point mutation: a change of a single nucleotide base in a DNA giving rise to altered amino acids in the polypeptide chains (e.g. Hb S , Hb C) Deletions and additions: Addition and deletion of one or more bases in the globin genes Unequal crossing over: as in Hb-lepore and Hb-antilepore associated with -thalassaemias. ________________________________________________________ *Most abnormal Hbs are produced by mutations in the structural genes which determine the amino acid sequence of the globin chains of the Hb molecule.

14 Geographical distribution of common Hb variants
Variant Occurrence predominantly in: Hb S (6GluVal) Africa, Arabia, Black Americans Hb C (6Glulys) West Africa, China Hb E (26Glulys) South East Asia Hb D (121GluGln) Asia Hb O (121GluVal) Turkey and Bulgury

15 Sickle Cell Haemoglobin
GAG GTG 6 Sickle Cell RBC Haemolysis

16 Inheritance of Sickle Cell Anaemia

17 Lungs ↑pO2 Red cell sickling Tissues ↓pO2

18 Major abnormalities & problems in SCA
Sickling of the red cell during deoxygenation, as the HbS has low solubility at low O2 partial pressure and precipitates. Chronic haemolytic anaemia due to repeated sickling in tissues and unsickling in the lungs. Plugging of microcapillaries by rigid sickled cells leading to sickle cell crises i.e severe pain and edema. This causes significant damage to internal organs, such as heart, kidney, lungs and endocrine glands. Repeated infections. Frequent cerebrovascular accidents. Hand-foot syndrome (in small,i.e.around age of 3y); Swollen hands and feet may be the first signs of sickle cell anemia in babies. The swelling is caused by sickle-shaped red blood cells blocking blood flow out of their hands and feet Bone deformation – bossing of the forehead. Hepato-spleenomegaly. Growth retardation. Frequent blood transfusion requirements. Psychosocial problems.

19 Clinical Features Management
Site of Sickling Clinical Features Management Bone Painful crises Pain relief and hydration. Hydroxyurea Lung Acute chest syndrome Transfusion regimen, pain relief and hydration Brain Stroke Transfusion regimen. Heart Myocardial infarction Spleen Acute splenic sequestration: Transfusion, pain relief and hydration Retina Proliferative retinopathy Retinal surveillance. Laser

20 Sickle Cell Trait Heterozygous state for HbS (HbAS)
No serious clinical consequences Sudden death during intensive training Hematuria, isosthenuria (renal papillary necrosis)

21 Thalassaemias Genetic disorders resulting from
decreased biosynthesis of globin chains of haemoglobin.

22 Thalassaemias A group ( not single identity) of Genetic defects.
Due to mutations in and around the globin genes. Decreased production of one or more of the globin chains. Result in an imbalance in the relative amounts of the - and non  -chains. Altered /non-  ratio. As a consequences of thalassaemias there is excess production of the other chains, and a decreased over all haemoglobin synthesis.

23 Types of Thalassaemias
* Most common - Thalassaemia

24 α Thalassemia Deletion of one or more alpha genes from chromosome 16
-a/aa: silent career with little signs --/aa: cis double deletion more common in SEA -a/-a: trans double deletion --/-a: Hb H disease --/--: Hb Bart’s hydrops fetalis

25 Alpha thalassemia αα/αα Normal αα/α- Mild microcytosis αα/- - α-/α-
α-/- - Hemoglobin H disease - -/- - Hemoglobin Barts – Hydrops Fetalis

26 - Thalassaemia Hb - Decreased / ratio   In - Thalassaemia
production of - chains Normal =  - Thalassaemia Accumulation of 

27 Point Mutation producing - Thalassaemia
Less Frequent Introns Chromosome 16 5’ exon1 exon2 exon3 3’ Base Substitution 2bp del Chain Termination Defect 5bp del Poly A signal Mutation

28 Mutations Producing - Thalassaemia
Deletions Most frequent: Chromosome 16 / -/ -/- --/ --/- --/-- Normal -thal 2 hetero -thal 2 homo -thal 1 hetero HbH Disease Hydrops fetalis

29 - Thalassaemia-2 One  -gene deletion.
-chain production is only about 75% of normal. May be homo- (- /- ) or heterozygous (- / ) The patient usually shows a normal phenotypic appearance but there might be mild thalassaemia symptoms. Hypochromic-microcytic RBC’s due to partial reduction of -chain.

30 - Thalassaemia-1 Two  -genes deletion- (o ) thal.
The patient synthesizes -chain but it is decreased to about 50% of normal. Anaemic symptoms- hypochromic microcytic anaemia. May be homozygous (- -/- -) or heterozygous(--/ ). If the patient is homozygous than there is no -chain synthesis, and if heterozygous then there is decreased synthesis of the -chain to half normal level.

31 Hb H Disease Three -gene (three alleles) deletion.
The Hb present during foetal life is “Hb Bart’s” (4), while during adulthood the Hb present is “Hb H” (4). Some of the symptoms include: hepatosplenomegaly, impairment of erythropoiesis, and hypochromic-microcytic haemolytic anaemia.

32 Hydrops foetalis Homozygous o-thalassaemia.
There is a complete absence of -chain (all -genes are deleted). The Hb produced at birth is Hb Barts (4). Hydrops foetalis is lethal and the baby is born dead. Hydrops fetalis is a severe, life-threatening problem of severe edema (swelling) in the fetus and newborn. It is also called hydrops. Symptoms include: Hepatosplenomegaly, severe hypochromic- microcytic anaemia.

33 Hb - Thalassaemia     - Thalassaemia Increased / ratio
In - Thalassaemia Decreased production of - chains Normal =  - Thalassaemia Accumulation of 

34 Beta thalassemia Impaired production of beta chain
beta thalassemia minor – heterozygous (or trait) beta thalassemia major - homozygous

35 Types of - Thalassaemia
Thalassemia Major (Cooley's anemia) -severe form of beta thalassemia - presence of two abnormal genes that cause either a severe decrease or complete lack of beta globin production. Thalassemia Minor - presence of one normal gene and one with a mutation - causes mild to moderate mild anemia. Major -usually appears in an infant after three months of age and causes life-threatening anemia 35

36 Etiology of - Thalassaemia
Beta thalassemia is caused by a deficiency of Beta globin inherited in an autosomal recessive pattern, which means both copies of the HBB(Hemoglobin beta) gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.


38 Beta thalassemia trait
No symptoms Mild microcytic anemia

39 Beta thalassemia major
No beta chain produced (no HbA) Severe microcytic anemia occurs gradually in the first year of life Marrow expansion Iron overload Growth failure and death

40 - Thalassaemia Usually point mutation in the control region.
The absence of beta-globin is referred to as beta-zero (B0) thalassemia. Other HBB gene mutations allow some beta-globin to be produced but in reduced amounts. A reduced amount of beta-globin is called beta-plus (B+) thalassemia β+ has minimal production. β+/β+ or βo/βo is  thal major or Cooley’s anem Often not apparent at birth until β chain takes over γ chain production. High Hb A2, Hb F. Related: Hb Lepore (δ-β usion), High Persistence of Foetal Hb; (HPFH).

41 - Thalassaemia It is characterized by either no -chain synthesis (i.e. o) or decreased synthesis of -chain (+). Excess -chains precipitate in RBC’s causing severe ineffective erythropoiesis and haemolysis. The greater the -chains, the more severe the anaemia. Production of -chains helps to remove excess -chains and to improve the -thalassaemia. Often HbF level is increased. Majority of -thalassaemia is due to point mutation.

42 o-Thalassaemia The -chain is totally absent.
There is increase in HbF with absence of HbA. This is combined with ineffective erythropoiesis. In majority of the cases, -gene is present but there is complete absence of mRNA. Characteristics of this disorder are: Skeletal deformities (e.g. enlargement of upper jaw, bossing of skull and tendency of bone fractures). Severe hypochromic- microcytic anaemia. Survival depends on regular blood transfusion. This leads to iron overload (iron accumulates in the blood and tissues, causing tissue damage). Death usually occurs in the 2nd decade of life (i.e. at age of about 20 years) if measures are not taken to avoid iron overload by chelation therapy.

43 Mutations affecting the -Globin gene.
Chromosome 11 Mutations affecting transcription initiation Mutations affecting RNA splicing Mutations affecting translation initiation Non-sense Mutations. Mutations of polyadenylation site. >200 -Thal mutations reported to-date Worldwide

44 Clinical Classification of Thalassaemias
Thalassaemia major: The patient depends on blood transfusions especially if he is homozygous. Thalassaemia intermediate: Homozygous mild +-thalassaemia. Co-inheritance of -thalassaemia. Heterozygous -thalassaemia. Co-inheritance of additional -globin genes.  -thalassaemia and hereditary persistence of foetal Hb Homozygous Hb lepore Hb H disease. 3. Thalassaemia minor (trait): o-thalassaemia trait. +-thalassaemia trait. Hereditary persistence of foetal Hb only. -thalassaemia trait. o- and +-thalassaemia trait.

45 Beta thalassemia major treatment
Transfusion Iron chelation Stem cell transplant

46 Hb-Lepore This is an abnormal Hb due to unequal crossing-over of the - and -genes to produce a polypeptide chain consisting of the - chain at its amino end and - chain at its carboxyl end. The -fusion(hybrid) chain is synthesized inefficiently and normal  and -chain production is abolished. The homozygotes show thalassaemia intermediate and heterozygotes show thalassaemia trait. Chromosome 11 G A  5’ 3’

47 Hemoglobinopathy-antenatal diagnosis
Test partners of heterozygous or affected individuals Antenatal diagnosis from DNA obtained by chorionic villus sampling, or by amniocentesis


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