Detection of MLL-AF4 fusion transcripts in non-t(4;11) leukemic cells by PCR. Ethidium bromide–stained gel (A) and Southern blot (B) of the PCR reaction products from ALL patients who lack cytogenetically detectable t(4;11). First and last lanes contain molecular size markers. UPN-PEDS 69, 76, 86, and 106 had normal diploid karyotypes. UPN-PEDS 79 had a pseudodiploid karyotype. UPN-PEDS 43, 44, 57, and 59 had hyperdiploid karyotypes with structural abnormalities. UPN-PEDS 111 had hyperdiploid karyotypes without structural abnormalities. UPN-PEDS 87, a patient with t(4;11), was included as a positive control (see Tables 3 and 6).