RT-PCR analysis reveals skipping of FPGS exon 12 in RNA from ALL patient specimens. PCR was performed on cDNA prepared from 5 ALL patient specimens at first diagnosis (lanes 2, 4, 6, 8, 10, 12-14) and at relapse (lanes 3, 5, 7, 9, 11), using primer ex9-10 residing in the junction between exons 9 and 10 and primer EX13-dw (A), or ex11-13 residing in the junction between exons 11 and 13 and primer EX15-dw (B). (A) All samples (including CCRF CEM, lane 1) exhibited the expected 450-bp-long product, whereas relapse sample R1 (lane 3) displayed low levels of another 300-bp product. DNA sequencing corroborated the absence of exon 12 in this 300-bp product. (B) This diagnostic PCR results in a 250-bp product only when exon 12 is absent, and was obtained for relapse sample R1 (lane 3) and to a lower extent in 2 diagnosis samples D5 and D8 (lanes 10 and 14, respectively).