Acquired haemoglobin H disease.

Acquired haemoglobin H disease has been described in various premalignant haematological conditions and is most commonly associated with myelodysplastic and myeloproliferative syndromes. The condition is not restricted to any specific population group or geography. Affected individuals have no family or past history of alpha thalassaemia and these subjects usually suffer from severe uncompensated haemolysis. Extensive mapping and sequence analysis of the alpha globin gene cluster have demonstrated intact alpha globin genes, leading workers to conclude that an acquired in trans mechanism is responsible for the disorder. ATRX gene mutations on the X chromosome have been shown to be instrumental in the suppression of alpha globin gene expression. Despite recent advances in the understanding of its pathogenesis, the precise mechanism of acquired haemoglobin H disease remains a mystery.