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The frequency of the deleted glutathione-S-transferase theta 1 (GSTT-1) null genotype in myelodysplastic syndrome (MDS) patients has been discussed by several investigators. [1][2][3][4][5] To confirm which sequences are deleted in GSTT-1 cDNA, we used reverse transcription polymerase chain reaction (RT-PCR) methods. Seven patients with MDS were selected for this study. Genomic DNA and total RNA were extracted from bone marrow by standard methods. To detect the presence or absence of the GSTT-1 gene in genomic DNA, we used PCR with a pair of primers complementary to the 3Ј coding section of the GSTT-1 sequence. These primers give a PCR product of 480 bp (upper panel in Figure 1). Of the seven samples, three gave a PCR product of the expected size and four yielded no PCR product at all. RT-PCR for GSTT-1 was performed with a pair of primers complementary to the 5Ј coding section and 3Ј coding section of the GSTT-1 cDNA for amplifying the 623-bp band. Furthermore, as shown in the middle panel in the Figure, the three PCR-positive samples showed the expected 623-bp band on RT-PCR, and the four which gave no PCR product showed a 500-bp band on RT-PCR (838-bp ␤-actin band as a control is shown in the lower panel in the Figure). PCR analysis of individual DNA samples in patients with MDS suggested that the GSTT-1 locus is polymorphic. RT-PCR showed that deletion of a 123-bp sequence was present in cases with no 480-band according to PCR analysis of genomic DNA samples. These results suggest that Southern blotting analysis is necessary to confirm the null genotype for GSTT-1, and that PCR alone cannot detect the null genotype because of the deletion of the 123-bp sequence, consistent with the sequence of primers complementary to the 3Ј coding section of the GSTT-1 gene. Y MaedaThird