Array-CGH reveals hidden gene dose changes in children with acute lymphoblastic leukaemia and a normal or failed karyotype by G-banding.

A tiling path 33K BAC array was used to study 28 children with acute lymphoblastic leukaemia (ALL) who had normal or failed G-banded karyotypes. Twenty-two patients (79%) had a total of 135 copy number alterations (CNA) (69 gains and 66 losses); most of these patients showed CNA that were below the resolution of G-banding. Molecular cytogenetic and array comparative genomic hybridization results enabled the division of B-precursor ALL patients into five groups: high hyperdiploidy, intrachromosomal amplification of 21q, ETV6/RUNX1 rearrangement, others and no CNA. Apart from a shared deletion of 9p21.3, T-ALL patients had additional small CNA, with no region in common.