Table 1 Genotypes and phenotypes of thalassaemia

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 ⁺ /β ⁺ ,β ⁰ /β ⁺ , β ⁺ /β, β ⁰ /β, β ⁰ /β ⁰

Severity is very variable. Clinical picture ranges from mild to moderate NTDT

Major

β⁰β⁰ , β⁰/β⁺

Severe anaemia requiring regular transfusions (TDT)

HbE

HbE trait

β^E/β

Asymptomatic condition with no clinical relevance

Homozygous HbE

β^E/β^E

Usually asymptomatic with borderline asymptomatic anaemia and no haemolysis

HbE/ β-thalassaemia*

β ^E /β ⁺ ,β ^E /β ⁰

Severity is very variable. Clinical picture ranges from NTDT to TDT

HbE/HbS

β^E/β^S

Similar to sickle cell disease usually with rare vaso-occlusive crisis