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Table 1 Genotypes and phenotypes of thalassaemia

From: Identification and key management of non-transfusion-dependent thalassaemia patients: not a rare but potentially under-recognised condition

  VariantVariant GenotypeGenotype Phenotype
β-thalassaemia Normal αα/αα Normal
  Silent Carrier -α/αα Haematologically silent or mild reduction of MCH/MCV
  Minor -α/-α , - -/αα Borderline anaemia or normal, as well as microcytic and hypochromic red blood cells
  HbH disease* - -/-α , - -/αTα, αTα/αTα T - -/- - T α T α Majority have mild to moderate anaemia and marked microcytosis and hypochromia, only few have phenotype similar to thalassaemia major
  Barts Hydrops Foetalis - -/- - Most develop hydrops foetalis syndrome and die in utero, or shortly after birth
β-thalassaemia Normal β/β Normal
  Minor β/β++ , β/β00 Borderline anaemia or normal as well as microcytic and hypochromic red blood cells
  β-thalassaemia intermedia* β + + 0 + , β + /β, β 0 /β, β 0 0 Severity is very variable. Clinical picture ranges from mild to moderate NTDT
  Major β0β0 , β0+ Severe anaemia requiring regular transfusions (TDT)
HbE HbE trait βE Asymptomatic condition with no clinical relevance
  Homozygous HbE βEE Usually asymptomatic with borderline asymptomatic anaemia and no haemolysis
  HbE/ β-thalassaemia* β E + E 0 Severity is very variable. Clinical picture ranges from NTDT to TDT
  HbE/HbS βES Similar to sickle cell disease usually with rare vaso-occlusive crisis
  1. *Thalassaemia genotypes that often result in NTDT.