Alpha thalassemia Dr Mahmoud A Alhussain Consultant Paediatrician DHA 1 Outline • Introduction • Genotype phenotype correlation • Common alpha thalassemia syndromes • Clinically significant alpha thalassemias • Alpha thalassemia syndromes in UAE 2 Thalassemia syndromes • The major Hb in adults is HbA, 2 α and 2 β globin chains. • Globin chain synthesis is very tightly controlled • The ratio of α to non- α chains is 1.00 ± 0.05. • Thalassemia : a spectrum of diseases characterized by reduced or absent production of one or more globin chains: Disrupting this closely-regulated ratio • one of the world’s most common single-gene disorders. 3 2 globin gene switches • The embryonic to fetal switch (ε to γ and ζ to α), which starts very early in pregnancy and is completed at 10 weeks of gestation, • Fetal to adult switch (γ to β), which occurs during the perinatal period 4 β and β like globin gene ( chromosome 11) The two α globin genes (on chromosome 16). 5 Case 1 5year old boy has following results RBC 5.6 million Hb 10.1 MCV 62 MCH 19.9 MCHC 30.5 RDW 14.1 IRON studies normal Hb A – 94.8 % HbA2 –1.7 % HbF – 1.2% 6 α -thalassemia syndromes • A group of hereditary anemias of varying clinical severity. • Caused by deficient expression in one or more of the two α -globin genes on chromosome 16 • Characterized by the absence or reduced synthesis of α -globin chains. 7 ALPHA THALASSEMIA SYNDROMES • Impaired production of alpha globin chains, • Relative excess of β globin chains. • Excess beta globin chains have toxic effect on the red cell membrane skeleton (less than the excess alpha globin chains in beta thalassemia) • Normal subject have 4 functional alpha globin genes, • Two on each chromosome 16 (αα / αα). • There are 4 α thalassemia syndromes, reflecting the loss /inactivity of 1, 2, 3, or all the 4 of α genes 8 World distribution • The most common genetic disorder • Distribution parallels that of once common falciparum malaria • Selection benefit ,resistance to severe falciparum malaria 9 ALPHA THALASSEMIA SYNDROMES pathology • Less α chain produced :relative excess of non alpha globin chains. – Newborn (Hb bart’s:4 gamma) later (Hb H :4β) – Unstable and thermolabile . – Oxygen affinity more than 10 times that of hb A – Useless for oxygen transport . – Oxidized easily and tend to precipitate with cell aging – Aggregation within erythroid precursors is minimal, – Ineffective erythropoiesis is less than in severe beta thalassemia syndrome 10 2 molecular genetic types • Deletional – most common – compensatory increase in expression in the remaining functional α gene • Non-deletional – Less frequent – more severe effect on α-globin gene expression and more severe hematologic phenotype – No compensatory increase in expression in the remaining functional α gene 11 Thalassemias normal 4 Genes / chromosome 16 • -/: silent carrier with little signs • trait • --/: cis double deletion more common in SEA • -/-: trans double deletion • --/-: Hb H disease • --/-- : hydrops fetalis Hb Bart’s 12 Silent Carrier • Single α-globin gene defect (-α/αα). • α:β globin ratio 0.8 - 0.9. in reticulocytes • In the newborn (1 to 2%) of Hb Barts • Usually silent phenotype (normal red blood cell indices) • The diagnosis can be made only by DNA analysis. • Significance : (-α/αα). Mating with partner carrying cis type (αα/--) can give an infant with HbH disease. (-α/--) • How common (-α/αα). in UAE ?? 66%, 33%, 22%, 11% 13 Alpha thalassemia trait • α/β-globin chain synthesis ratio in the range of 0.7- 0.8. • Resembles mild β thalassemia trait. • May have mild anemia, • RBC hypochromic , microcytic ,target cells • Hb electrophoresis normal. • 2 types – Trans (α -/ α -). In UAE – "cis" (α α /--). Asian populations • Definite Diagnosis : only by molecular genetics • In the newborn Hb Barts (5 to 6%) and MCV less than 94 14 Genotype/phenotype correlation Typical phenotype of the α-thalassemia trait • Deletional (α-/α -) or (αα/ --). • Double heterozygotes for deletional /nondeletional (-α/[αα]T) • Homozygotes for nondeletional defects ([αα]T/[αα]T) • Rarely homozygotes for some nondeletional forms may have a mild HbH disease like Hb Constant Spring mutation 15 Alpha trait • 3y boy Newborn • RBC 5.79 RBC 6.7 • Hb 10.6 Hb 18 MCV 84 • MCV 57.6 MCH 26 • MCH 18.3 Hb Barts 4.9% • Retics 1.6 Homozygous for the 3.7kb deletion • homozygous for the (-a3.7kb / -a3.7kb ) 5-nucleotide deletion • (-5nt del/-5nt del) How common α trait in UAE ? 33%, 22%, 11% 16 α trait and βTT • The co-inheritance βTT with α-trait: might normalise MCV and MCH, • HbA2 levels remain elevated within the range for βTT, • Practical point :premarital screen – If HbA2 determination is always performed , double heterozygotes for β- and α-thalassemia will not escape diagnosis of βTT.(UAE) – If HbA2 determination only in those individuals with reduced MCV and MCH may escape the diagnosis of βTT. 17 α trait and βTM • Coinheritance of α trait ameliorates the severity of βTM, • Reduction in α globin synthesis reduces the burden of α globin inclusions without greatly affecting the amount of actual hemoglobin made 18 Sickle cell trait and α trait αα/αα -α/αα -α/-α HbS (%) 35 - 39 29 - 34 24 - 28 MCV (fL) 80 - 90 75 - 85 70 - 75 Greater affinity of β A chains than of β S chains for α chains Excess βS chains presumably are destroyed by proteolysis 19 Sickle cell anaemia and alpha trait • Beneficial effect on sickle cells – Anemia is significantly milder – MCH less – RBC deformability is better • However higher Hb and blood viscosity. – More VOC – More osteonecrosis – More retinopathy • While the overall clinical phenotype may be improved, • ?? increases survival in patients with sickle cell anemia 20 α trait and HPP/HE Latifa Hospital 21 GENETIC COUNSELING AND ANTENATAL DIAGNOSIS • Alpha thalassemia Trans (-α/-α). – Unlikely to give birth to infants with severe forms of alpha thalassemia. – Counseling to make individuals aware of the condition is usually adequate • Hemoglobin H disease or hydrops fetalis Cis ( - -/αα) – Families in which HbH or hydrops fetalis has previously occurred are clearly at risk of giving birth to additional infants with these conditions 22 Alpha thalassemia Trans (-a/-a). More than 11% of UAE nationals – are rarely at risk for giving birth to infants with severe forms of alpha thalassemia. – Counseling to make individuals aware of the condition is usually adequate – -a/-a -------------- -a/-a -a/-a 23 Clinically significant alpha thalassemia HbH Hydrops fetalis Hb Barts 24 18months T • RBC 5.29 GENOTYPE/MUTATION: • Hb 9 PolyA1(AATAAA->AATAAG)/--MED-I very large deletion(Alpha-Thal-1) combined • MCV 65 with non deletional alpha thal mutation, • MCH 17 resulting in severe alpha thalassemia(Hb H DISEASE) • RDW 24 • Retics 5.6% 25 HbH disease • observed in individuals from Southeast Asia • ( - -/-α ) 3 gene deletions/ • High β / α -globin synthetic ratio • The excess β chains HbH(4 β) 5-30% of Hb – high affinity for oxygen :10 times of HbA – Ineffectively supplies oxygen to the tissues – Defective oxygen-carrying capacity more severe than expected for level of Hb concentration 26 Age of presentation • Variable ,occurs in all ages • Usually present in the first years of life, • May not present until adulthood • May be asymptomatic diagnosed only during routine hematologic analysis • Neonates often have anemia, with severely hypochromic red blood cells, and high levels of Hb Barts (gamma 4). (This is in contrast to beta-chain disease) – a-chains are required for production of all forms of Hb, 27 Clinical presentation chronic hemolytic anemia – episodes of severe pallor and anemia. – Infections or drugs may precipitate hemolytic episodes. • Physical: • pallor, • jaundice, • hepatosplenomegaly, • Skeletal changes • pigment gallstones, 28 HbH Diagnosis • blood : hypochromia microcytosis • inclusion bodies with a supravital stain • HbH (5 - 30 %), on Hb electrophoresis • Hb Barts 20 to 40 %t at birth • DNA- for precise diagnosis, 29 30 Manegement Picture of thalassemia intermedia -non transfusion dependent – Hb levels usually range from 7-10 g/dL. – Transfusions may be needed – periodically or in periods of severe anemia, during parvovirus infections. Or when symptomatic • iron overload may require chelation therapy • In very severe cases, BMT may be considered, 31 Alpha 0 Hydrops fetalis , Hb Barts • Hb Barts (gamma-4 tetramers) cannot release oxygen to tissues • Cannot make normal neonatal and adult hemoglobins (ie, Hb A, F, and A2) • incompatible with extra uterine life 32 Alpha(0) thalassemia hydrops fetalis Hb Barts Usually die in utero or shortly after birth • Predisposis to toxemia of mothers • Maternal complications : – preeclampsia, polyhydramnios or oligohydramnios, antepartum hemorrhage, premature delivery. 33 Hb Bart syndrome shifting prognosis • Prenatal diagnosis, • Intrauterine blood transfusions, • Improved transfusion strategies, • (Rarely) curative hematopoietic stem cell transplant • Clinical trials : are lacking. Surviving number is small • Ethical dilemmas for the family and health care provider. 34 Hb Barts survivors(total n = 69) [Pecker et al 2017]. Age :0-5y (42%) 5y-10 y (30%) >10y (26%) GA at birth, wk ≥37w (28%) 30-36w (55%) <30w(13%) Current status Transfusion-dependent 53 (77%) Transplanted 14 (20%) Deceased*2 (3) A high frequency of congenital abnormalities 2/3d At least 1 anomaly 35 alpha thal in UAE • DNA study on newborns 419 consecutive newborns of UAE national mothers. • 49 % of the neonates had α-thal, (one of the highest in the world). • -α3.7/αα: 34%;