Summary The myelodysplastic syndromes (MDS) comprise a heterogeneous group of clonal disorders of the haematopoietic stem cell and primarily involve cells of the myeloid lineage. Using cDNA microarrays comprising 6000 human genes, we studied the gene expression profiles in the neutrophils of 21 MDS patients, seven of which had the 5q‐ syndrome, and two acute myeloid leukaemia (AML) patients when compared with the neutrophils from pooled healthy controls. Data analysis showed a high level of heterogeneity of gene expression between MDS patients, most probably reflecting the underlying karyotypic and genetic heterogeneity. Nevertheless, several genes were commonly up or down‐regulated in MDS. The most up‐regulated genes included RAB20, ARG1, ZNF183 and ACPL. The RAB20 gene is a member of the Ras gene superfamily and ARG1 promotes cellular proliferation. The most down‐regulated genes include COX2, CD18, FOS and IL7R. COX2 is anti‐apoptotic and promotes cell survival. Many genes were identified that are differentially expressed in the different MDS subtypes and AML. A subset of genes was able to discriminate patients with the 5q‐ syndrome from patients with refractory anaemia and a normal karyotype. The microarray expression results for several genes were confirmed by real‐time quantitative polymerase chain reaction. The MDS‐specific expression changes identified are likely to be biologically important in the pathophysiology of this disorder.

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Telomere shortening is associated with disease progression in chronic myeloid leukaemia (CML). To investigate the biology and regulation of telomerase in CML, we evaluated expression of the telomerase components, its regulators and several telomeric-associated proteins. Quantitative real-time-polymerase chain reaction (PCR) was used to compare gene expression in the CD34 þ /leukaemic blast cells of 22 CML patient samples to the CD34 þ cell population of healthy individuals. hTERT, the catalytic component of telomerase, was downregulated in eight of 12 chronic phase (CP) patients (P ¼ 0.0387). Furthermore, hTERT was significantly downregulated in two of three patients in accelerated phase (AP) and seven of seven patients in blast crisis (BC), P ¼ 0.0017. Expression of hTR and telomericassociated proteins TEP1, TRF1, TRF2, tankyrase and PinX1 was high in the majority of CP and AP patients. With the exceptions of TEP1 and hTR, expression of these factors was highest in CP and decreased during disease progression. Expression of c-Myc, a positive regulator of hTERT transcription, correlated with hTERT expression and decreased with disease progression, falling below control levels in BC. hTERT levels were increased in CP patients following successful treatment with imatinib, relative to untreated CP patients. We suggest that reduced hTERT expression directly causes the shortened telomeres observed in CML.