The molecular genetic analysis of gene rearrangements in acute lymphoblastic leukaemia.

In ALL the majority of cases possess clonal rearrangements of the Ig or TCR gene loci. Detection of these clonal markers by Southern blot analysis over a disease course has provided information on the fate and origin of leukaemic clones during treatment. Detection of these gene rearrangements has been used to detect residual disease during treatment. More recently, methods have been developed for the detection of Ig and TCR gene rearrangements using the polymerase chain reaction (PCR). This amplification technique allows for the rapid detection of gene rearrangements with a greater sensitivity than more conventional methods. The full impact and usefulness of this technique in residual disease detection has yet to be determined. The presence of the Philadelphia chromosome t(9;22) in ALL is associated with poor prognosis. Its detection by Southern blot is technically complicated due to the heterogeneity of chromosome breakpoints involved. The development of PCR-based methods for the detection of the bcr/abl mRNA associated with the Philadelphia chromosome has improved our understanding of the significance and incidence of this disease marker in ALL, emphasizing the importance of establishing Philadelphia status on all patients at diagnosis. Although longitudinal studies in CML have shown the presence of bcr/abl mRNA to be associated with residual disease, and its absence associated with long-term remission, these studies have yet to be reported for ALL. The usefulness of detection of residual disease using bcr/abl has yet to be determined.