Detection of genetic defect of childhood acute leukaemia by reverse transcriptase polymerase chain reaction (RT-PCR): An essential component for risk directed therapy approach

Abstract

OBJECTIVE: As the outcome of childhood acute leukaemia improved with the current therapeutic regimens, attempts to differentiate good and poor risk leukaemia based on the underlying genetic abnormality becomes important. These information can help us to decrease the treatment related toxicity for the good risk leukaemia and increase the treatment intensity for the poor risk leukaemia so maximum therapeutic advantage can be achieved. In order to attain this goal, an accurate and cost effective genetic diagnostic method should be developed. METHODS: Children with newly diagnosed acute lymphoblastic leukaemia (ALL) and acute myeloid leukaemia (AML) at 4 public hospitals from Jan. 96 to June 97 were studied. Their genetic abnormalities were analyzed by both cytogenetic and molecular methods. The molecular methods included the standard and multiplex RT-PCR techniques. The multiplex RT-PCR approach can simplify and combine different PCR reactions into one reaction. Four common childhood ALL genetic defects [poor risk: t(9;22), t(4;11), intermediate risk: t(1;19), good risk : t(12;21)] and 3 common childhood AML genetic defects [all good risk: t(15;17), t(8;21), Inv 16] can be studied by these molecular techniques respectively. All of these translocation changes account for 20 to 30% of genetic anomalies in acute leukaemia of childhood. RESULTS: Within this 1.5 years, 14 cases of newly diagnosed childhood ALL (QMH n=11, Others n=3) and G cases of newly diagnosed childhood AML (QMH n=4, Others n=2) were included in this study. Of the 14 ALL patients (median age: 4 yrs), 11 could be studied by cytogenetic method. t/11 were found to haven genetic abnormality by karyotyping. On the other hand, all of these 14 ALL patients were successfully studied by the RT-PCR multiplex method. Four were found to have t(12;21) anomaly and they were not detected by the karyotyping method Of the 6 AML patients (median age: 12 yrs), 4/6 had cytogenetic abnormality detected by karyotyping and 3/4 were simultaneously picked up by the RT-PCR technique. These information were subsequently utilized in assisting the assignment of patients into the various alms of the risk directed treatment protocols for childhood leukaemia. CONCLUSION: Our results showed that both cytogenetic and molecular methods are important in diagnosing the genetic abnormalities of childhood leukaemia. Both methods can compensate the shortcoming of each other. The genetic information derived from these methods has become an indispensable part of the risk directed therapeutic approach for childhood leukaemia currently. Therefore, the cost effective multiplex RT-PCR approach should be utilized more extensively. The additional potential use of RT-PCR as a mean to detect early residual disease is currently being studied.