THALASSEMIA Hope Y. Agbemenyah

The hemoglobin is critical for gaseous exchange and transportation between tissues. Hemoglobins are encoded in two tightly linked gene clusters; the α-like globin genes are clustered on chromosome 16, and the β-like genes on chromosome 11. The α-like cluster consists of two α-globin genes and a single copy of the ζ- gene. The non-α gene cluster consists of a single ε gene, the G γ and A γ fetal globin genes, and the adult δ and β genes. Thalassemias are heterogeneous group of inherited haemoglobinopathies due to mutations leading impaired α- or β- globin biosynthesis. - diminished production of adult haemoglobin tetramers HbA (α 2 β 2 ): hypochromic and microcytic anemia. -increased cell membrane damage or ineffective erythropoiesis or both Thalassemia syndromes

Demographics and Epidemiology Certain ancestry: endemic in the Mediterranean basin, Middle East, Asian and tropical Africa and the Indian subcontinent ancestry. Distribution parallels that of Plasmodium falciparum

Molecular Pathogenesis Mutations Trancriptional: Promoter region mutations – Inability to recruit transcription factors eg GATA-1, NFE-2, the SWI/SNF-like protein called ATRX Posttranscriptional: mRNA processing – Splicing mutations some normal beta globin – β + - Thalassemia (reduced but detectable β-globin synthesis) Translational: Chain termination mutation – de-novo stop codon and indel blocking translation – β o - Thalassemia (absent β-globin) – Deletion: α-Thalassemia Deletion: α-Thalassemia Other causes α-protein stabilizing protein (AHSP)

Classifications α-Thalassemias due to deletions that cause reduced or lack of synthesis of alpha globin chain. hence unpaired gamma globins (fetal) or beta (adults) these are soluble so hemolysis and ineffective erythropoiesis is less severe than beta thalassemia. ThalassemiaGenetic mutationRemarks Silent carrier-α/ααNo effect α-Thalassemia trait Minor -α/-α --/αα Slight anemia Hb H, β 4 --/-αSeverely anemic and susceptible to oxidation Barts hydrops fetalis, γ 4 --/--Lethal

Classifications β-Thalassemias variable mutations leading to increased levels of alpha globin proteins ThalassemiaGenetic mutationRemarks β-Thalassemia traitβ/β o or β/β + Mild anemia and small RBCs due to lack of Hb β-Thalassemia intermediaMilder variant of β + /β + or β o /β + Significant lack of Hb, Moderate anemia β-Thalassemia majorβ o /β o, β o /β + or β + /β + Severe anemia accumulation of highly insoluble unpaired α chains. They form toxic inclusion bodies that kill developing erythroblasts in the marrow, few escape with membrane damaging insoluble α chains that undergo extravascular lyses Provoking compensatory erythroid hyperplasia but the marrow is sabotaged by ineffective erythropoiesis. Persistence of anemia causes exuberant extramedullary erythropoietic tissues recruitment

Clinical presentations Despite differences in the molecular mechanisms underlying the cause of the disease patients generally present common symptoms of severe tissue hypoxia, hemolytic anemia, marked hepatomegaly, marked erythroid hyperplasia, iron overload Other symptoms include fatigue, weakness, pale appearance, excessive hemolysis leading to yellowish discoloration of skin (jaundice), facial bone deformities, dark urine. The signs and symptoms the patient experiences depend on the type and severity of thalassemia. Hyperplasia of bone marrow and extramedullary erythropoiesis

Diagnosis β-Thalassemia major: basis of severe microcytic anemia, ineffective erythropoiesis- hepatosplenomegaly, and elevated levels of HbF, HbA 2 or both Intermedia exhibit similar stigmata but can survive without chronic hypertransfusion Minor: profound microcytosis and hypochromia with target cells, but only minimal or mild anemia. Mean corpuscular volume is rarely >75fL; hematocrit is rarely <30- 33%. Hb electrophoresis reveals normal/elevated HbA 2 or normal/elevated HbF α-thalassemia trait- mild hypochromia and microcytosis usually without anemia Hb electrophoresis Microcytosis and hypochromia Reduction in HbA and increase in Hb F Increased RBC count for such level of anemia

Diagnosis Blood smear shows – Anisocytosis (marked variation in size) – Poikilocytosis (variation in shape) – Target cells ( accumulation of Hb in the center of the cell) Basophilic stippling Enlargement of cheekbones and other bony prominence

Treatment Blood transfusion and as complication you treat iron overload iron chelator- deferoxamine or deferasirox – Cardiac disease resulting from progressive iron overload and secondary hemochromatosis- an important cause of death Regular monitoring of extramedullary hematopoiesis and spleen size (Splenectomy) Hydroxyurea (established) and HDACi (worth testing experimentally) indicated in patients with extramedullary hematopoiesis and leg ulcers Allogenic stem cells transplantation is the only curative therapy Vitamin D supplementation Gene therapy, lentiviral constructs expressing corresponding correct gene Premature Termination Codon treatment by the use of aminoglycosides

Prevention Antenatal diagnosis DNA diagnosis by PCR amplification of fetal DNA obtained by amniocentesis or chorionic villus biopsy which is then hybridized to allele-specific oligonucleotide probes This examination is only appropriate if both parents are known to be carriers (β- Thalassemia minor) and will accept a termination Seek genetic counseling if a carrier of α-Thalassemia gene Assisted reproductive therapy

Differential Diagnoses Anemia of Chronic Disease and Renal Failure Lead Nephropathy Lead poisoning Sideroblastic Anemias

Case A 10-month-old boy of Arabic extraction is brought to the physician by his parents who complain that their child is failing to thrive. Physical examination reveals splenomegaly and jaundice. A CBC shows a microcytic, hypochromic anemia (hemoglobin = 7.4 g/dL). Fetal hemoglobin accounts for most of the hemoglobin. A peripheral blood smear is shown in the image. Which of the following is the appropriate diagnosis? What is the pathogenesis of splenomegaly seen in the patient described above

Adriana is a 7-year-old who lives with her parents in a surburban community. Her parents brought her to the united states from their homeland in Greece when she was 1 year old. At the of 3, she was in the 10 th percentile for her height and weight, pale and her hemoglobin was 5.8 g/dL. Following further diagnostic studies, she was diagnosed with beta-thalassemia major. Over the course of the next 4 years, Adriana was hospitalized every 1-2 months so she could be transfused with packed red blood cells. Case study During a routine follow-up visit at the hematology clinic, Adriana’s laboratory results were as follows: Hemoglobin: 10 g/dL Total serum iron: 150 g/L As hematologist, you discuss planned treatment with Adriana and her parents

What are the clinical manifestations of b- Thalassemia? What are the priorities of care for Adriana? Which options are available for Adriana to prevent life-long blood transfusion?

References Pathology by Kumar and Robbins Harrison’s principles of internal medicine 17 th ed McGraw-Hill Davidson’s principles and practice of internal medicine 20 th ed McGraw-Hill

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