Molecular cytogenetic findings of acute leukemia included in the Brazilian Collaborative Study Group of Infant acute leukemia

Abstract

Background: Chromosome abnormalities often occur prenatally in childhood leukemia, characterizing an early event in leukemogenesis. The majority of the abnormalities occurring in infants involve the MLL gene on chromosome band 11q23. We describe the molecular cytogenetic findings of 207 infant acute leukemia (IAL) cases included in the Brazilian Collaborative Study Group of Infant acute leukemia.

Procedure: The diagnosis of Acute Lymphoblastic leukemia (ALL) or acute myeloblastic leukemia (AML) was made according to morphology and immunophenotyping classification, followed by conventional karyotyping. Samples were then screened using RT-PCR for the presence of specific chromosome translocations. FISH assay for MLL rearrangements was performed only in cases with negative or inconclusive cytogenetic or PCR results.

Results: The characteristics of children with IAL were as follows: 115 boys and 92 girls, age range 0-23 months, mean age 12 months, 145 ALL, and 62 AML. A statistically significant association was observed between pro-B ALL cases and MLL+ve (P=0.0001) cases and the age group 0-3 months with MLL+ve (P=0.008) cases. Two rare cases of pro-T ALL with MLL+ve were found. Other than MLL rearrangements, various other molecular aberrations were detected including TEL/AML1+ve (n=9), E2A/PBX1+ve (n=4), PML/RARA+ve (n=4), and AML1/ETO+ve (n=2). Cytogenetic analysis revealed hyperdiploidy (n=6), del(7) in two cases and del(11)(q23) in seven cases.

Conclusions: Our results show that not only MLL rearrangements, but also other molecular abnormalities occur before birth and may contribute to leukemogenesis.