Lanes: 100 bp molecular weight ladder (New England Biolabs, Cambridge, Massachusetts); 1, MDS patient sample RT-PCR product, amplified using primer pair: 5′-CCTCTTGCTCCACCCATCAAAC-3′ (MLL exon 6, sense strand) and 5′-CGCCCAGGTCCTGGAATTT-3′ (SEPT9 exon 3, antisense); 2, wild-type control with same primer pairs; 3, patient PCR product using primer pair: MLL exon 6, sense, as above, and 5′-TTCTCCACCTGCTTGGACGAG-3′ (SEPT9 exon 3, antisense); 4, wild-type control with same primer pairs. Transcript variant 3 (Figure 3) is predicted to have a 608 bp product using the primer set in lane 3 and 448 bp product using the primer set in lane 1, which is what is observed. Product identity was verified by DNA sequencing.