This study is highly significant

Leukaemia Research Fund spokesman

This newly identified form of leukaemia possesses what is termed a chromosomal translocation. In this case, that means that a piece of chromosome 11 has broken off and attached itself to another chromosome.

Dr Stanley Korsmeyer and colleagues found that patients with this chromosomal translocation have gene expression profiles that are distinct from other leukaemias.

They concluded that these profiles distinguish this form of leukaemia from other types.

"Gene expression profiles of lymphoblastic leukaemia that possess an MML translocation are remarkably consistent and differ significantly from those of other leukaemias," they wrote in this week's issue of Nature Genetics.

"We therefore propose that they should be considered a distinct disease termed 'mixed lineage leukaemia'."

Highly significant

A spokesman for the Leukaemia Research Foundation said: "This study is highly significant".

He added: "What has been unclear until now is whether the poor survival rates of patients with this type of leukaemia was down to host factors, the fact that they are infants, or whether the tumour was significantly different.

"The result of these studies have shown that the tumour is biologically different and that has obvious implications for treatment and designing new treatments."