KW Chik, E Yung, P Tam, MK Shing, CK Li, MP Yuen

Introduction: Wilms tumour gene (WT1) is a tumour suppressor gene located at chromosome 11p13 in human. It encodes a transcription factor of the zinc finger family and represses the transcription of many growth factors. Normal expression is found in fetal kidneys, gonads and primitive haematopoietic cells. Four transcripts can be generated from WT1 that differ in the exon 5 expression and the inclusion of Lys-Thr-Ser (+/- KTS) between the zinc finger 3 & 4. The aberrant expression of the WT1 gene is found in different types of human leukaemia at diagnosis and relapse, suggesting a role in leukaemogenesis. We report the local experience of detection of the expression of WT1 in childhood leukaemia.

Methods: Children diagnosed leukaemia were included in the study. Diagnosis of leukaemia was based on FAB classification, immunophenotyping and cytogenetic analysis. Bone marrow obtained at diagnosis was subjected to RNA extraction, reverse transcription and nested polymerase chain reaction amplification by standard methods. The primers flanked the exon 7 and 10 of the WT1 gene. Negative control was included in all experiment.

Results: 23 children (ALL 9, AML, 9, CML, 5) were studied. No identifiable aberration involving chromosome 11p was noted on karyotyping. 2/9 of ALL, 5/9 of AML, 2/5 CML in chronic phase showed WT1 expression in our group of patients. Thus, 40% of these patients with leukaemia possess this informative marker.

Conclusion: Our preliminary results confirm the expression of the WT1 mRNA in various childhood leukaemia. More subjects will be needed to generate a better understanding of its expression pattern in leukaemia. This informative marker will serve as a mean to detect minimal residual disease of leukaemia in selected group of patients. The expression of this tumour suppressor gene in human leukaemia may shed light on the understanding of the pathway of leukaemogenesis.