Beta thalassaemia trait (carrier)

Thalassaemia minor refers to individuals who are heterozygous for the thalassaemic gene (i.e. beta thalassaemia carriers), either:

• heterozygous for beta+ - ie. beta+/beta; or
• heterozygous for beta0 - ie beta0/beta

The carrier incidence of beta thalassaemia in the UK amongst Asian communities is (1):

• 1 in 7 to 1 in 10 for Gujeratis
• 1 in 10 for Sindis
• 1 in 20 for South Indians
• 1 in 25 for Pakistanis
• 1 in 15 to 1 in 30 for Punjabis and Bangladeshis

In people from areas of the world without malaria the incidence is much lower e.g. 1 in 1000 English caucasians are beta thalassaemia carriers.

Affected individuals are usually asymptomatic and anaemia, when present, is mild. Thalassaemia trait is believed to offer resistance against falciparum malaria, accounting for it's prevalence in those parts of the world where malaria is endemic.

The red cells are hypochromic and microcytic and there is a low MCV and MCH. Confusion with iron deficiency anaemia is avoided as:

• serum iron and serum ferritin are normal and serum electrophoresis shows a raised Hb-A2 and usually a raised Hb-F
• the red blood cell count is increased; in iron deficiency it is low
• iron supplements are of no benefit in thalassaemia minor

Recognition of beta-thalassaemia trait is important as it permits subsequent genetic counselling.

Reference:

1. British Journal of Haematology (1991), 78, 242-7.