ACW Lee, KW Wong, LC Chan, SF Liu, KT So

Introduction Children with constitutional chromosomal aberrations are more prone to develop malignancies. Down's syndrome, in particular, is associated with a 10-20 folds of increased risk of acute leukaemias. With regard to acute lymphoblastic leukaemia (ALL), the commonest neoplastic disorder of childhood, children with Down's syndrome have not been found to be different from other children in terms of leukaemic morphology, immunophenotypes and cytogenetic findings. We describe and review the finding of acquired chromosomal translocation (8;14)(q11;q32) and suggest an association with ALL occurring in Down's syndrome.

Case Report A 4 1/2-year-old boy was diagnosed to have Down's syndrome soon after birth with a karyotype of 47, XY, +21. Acute lymphoblastic leukaemia was diagnosed with the following findings: hemoglobin 8.0 g/dl, white cell count 30.22 x 10⁹/l with 85% blasts, platelet 12 x 10⁹/l. The bone marrow smear was replaced by lymphoblasts of FAB Li morphology and an immunophenotype of common ALL. Cytogenetic study revealed a karyotype of 47, XY, t(8;14)(q11;q32), +21. Remission was attained and maintained according to the HKALL protocol.

Literature Review A total of 10 cases of ALL associated with t(8; 14)(q11;q32) have been reported. There was an excess of the male gender (9 cases) and a young age (7 cases under 16 years old). Most patients had B-lineage ALL expressing CD 10. Two children had null ALL. Three patients had additional chromosomal translocation (9;22)(q34;q11). With inclusion of the present case, three out of the eleven patients (27%) are also suffering from Down's syndrome.

Conclusion As t(8;14)(q11;q32) is a rare cytogenetic finding (< 1%) in, and patients with Down's syndrome constitute only a minority (< 2%) of, acute lymphoblastic leukaemia, the association between the acquired chromosomal translocation and Down's syndrome with ALL is striking. Further studies on the molecular events, which may involve the immunoglobulin H gene on 14q32 and the IL7 locus which is involved in lymphopoiesis on 8q11, may provide a hint to the pathogenesis of ALL in Down's syndrome.

Acknowledgement We thank Miss LM Ching for the cytogenetic analysis.