RFC mRNA in ALL blasts from newly diagnosed patients. (A) Relative RFC mRNA expression in nonhyperdiploid T-lineage lymphoblasts (n = 8), nonhyperdiploid B-lineage lymphoblasts (n = 14), and hyperdiploid B-lineage lymphoblasts (n = 7). Diamonds (⧫, ◥) depict lymphoblasts isolated from peripheral blood before treatment, squares (▪, ░) depict lymphoblasts from bone marrow before treatment, and circles (•) depict lymphoblasts from bone marrow 44 hours after MTX treatment. Shaded symbols depict nonhyperdiploid blasts and solid symbols depict hyperdiploid blasts (>50 chromosomes). Horizontal lines depict the median values in each group. (B) RFC mRNA expression in B-lineage ALL blasts with either 2 (n = 11), 3 (n = 5), or 4 (n = 5) copies of chromosome 21. Symbols are the same as in (A). Among lymphoblasts with 3 copies of chromosome 21, the 2 samples with the lowest RFC expression have less than 50 chromosomes, and the lowest value had a translocation involving the long arm of 1 copy of chromosome 21 and the short arm of chromosome 12 (ie, a 12;21 [p13;q22] translocation) resulting in the ETV6-CBFA2 fusion. Similarly, among those with 4 copies of chromosome 21, the sample with the lowest RFC expression had less than 50 chromosomes.