BTG1 copy number loss is observed in approximately 10% of pediatric pre-B ALL cases. Genomic profiles of the chromosome 12q21.31-23.1 segment in 4 pre-B ALL cases. Indicated is a region less than 300 kb in size containing the BTG1 gene, with the positions of the 2 hypothetical proteins FLJ30877 and BC044741 and the SNPs represented on the array.