Alpha thalassaemia in an Irish family — a previously unreported finding

Summary

All forms of thalassaemia are uncommon in North Europeans and alpha thalassaemia to date has not been reported in the Irish context. We describe such a finding in a family with no known foreign ancestry and discuss the haematological investigations which led to its detection.

Haemoglobin is composed of two pairs of polypeptide chains each with its own haem group. At birth haemoglobin F predominates (α2π2). This is replaced during the first year of life by haemoglobin A₂ (α₂β₂). In both instances production of α chains is essential.

Two genes on chromosome 16 are concerned with α chain production. In α-thalassaemia one or both genes may be deleted. Two gene deletion is common in the people of South East Asia, whereas one gene deletion is found in subjects from the Middle East and Africa. It is possible therefore to have one, two, three or four gene deletion depending upon heterozygous or homozygous inheritance and racial admixture. Reduction in α-chain production leads to synthesis of Hb Barts (μ₄) and Hb H (β₄) tetramers. These tetramers are deleterious to the normal maturation of red cell precursors.

Four gene deletion is inimicable to life and deathin utero results. Three gene deletion leads to Hb H disease which is associated with marked haemolytic anaemia. Two and one gene deletion on the other hand produces a hypochromic blood picture very similar to iron deficiency with mild or absent anaemia. While Hb Barts may be detected in the neonatal period α-thalassaemia traits (one or two gene deletions) cannot be specifically diagnosed without α/β globin chain synthesis ratios.

Though β-thalassaemia has been reported in subjects of apparently unmixed Irish descent, no case of α-thalassaemia has been documented. We report one Irish family with α-thalassaemia trait.