Detection of multiple minor leukemic clones with internal tandem duplication mutation by Δ-PCR. The two wild-type peaks were 328 bases (blue) and 353 bases (green). Four mutant clones (M1, M2, M3, and M4) were detected. Each clone has one blue peak and one green peak, with a Δ value of 25 bases. The peak height ratio of M4/M2 was 6.4%, ratio of M2/wild-type was 6.2%, and the ratio of M4/wild-type was 0.4% (6.4% × 6.2%). *The red striped line within the 353-base wild-type peak indicates off-scale height. The PCR product was therefore diluted fivefold and reinjected into the ABI 3100 genetic analyzer (data not shown) to calculate the ratio of M2/wild-type.