Frequent co-expression of HoxA9 and Meis1 genes in infant acute lymphoblastic leukaemia with MLL rearrangement.

We studied the expression of HoxA9 and Meis1 by reverse transcriptase-polymerase chain reaction analysis in leukaemic cells from cases of infant acute lymphoblastic leukaemia (ALL, n = 27) and childhood ALL (n = 29). These two genes were co-expressed significantly more frequently in infant ALL than in childhood ALL (19/27 vs0/29 cases, P < 0.001) and were highly associated with MLL gene rearrangement in infant ALL cases (P < 0.001). These findings indicate that the HoxA9 and Meis1 genes are closely associated with MLL gene rearrangement in the development of infant ALL, which represents a distinct entity of childhood ALL.