MicroRNA (miRNA) profiling reveals distinct signatures in B cell chronic lymphocytic leukemia (CLL). This study used a microarray containing hundreds of human precursor and mature miRNA oligonucleotide probes to perform genome-wide expression profiling of miRNAs in CLL samples and normal CD5+ B cells. The results showed significant differences in miRNome expression between CLL samples and normal CD5+ B cells, confirmed by Northern blot and real-time RT-PCR. Two distinct clusters of CLL samples were identified based on the presence or absence of Zap-70 expression, a predictor of early disease progression. Two miRNA signatures were associated with the presence or absence of mutations in the expressed Ig variable-region genes or with deletions at 13q14, respectively. These findings suggest that miRNA expression patterns are relevant to the biological and clinical behavior of CLL. MiRNAs are small, non-coding RNA molecules that regulate gene expression. They are involved in various biological processes, including cell proliferation, cell death, stress resistance, and fat metabolism. The study found that miRNA expression patterns differ between normal and neoplastic cells, and that miRNAs may play a significant role in the pathogenesis of human cancer. The miRNA microarray chip developed in this study allows for the analysis of miRNA expression in various human tissues, revealing distinct miRNA signatures for different tissue types. The study also found that miRNA expression profiles differ between CLL cells and normal CD5+ B cells, with several miRNAs located within fragile sites showing distinct expression patterns. The study further demonstrated that miRNA expression in CLL is associated with clinical and biological factors, such as the levels of ZAP-70 and the presence of mutations in the IgVH genes. The results suggest that miRNA expression profiles have prognostic significance in CLL. Additionally, the study found that miRNA expression is inversely correlated with the levels of Pten protein in CLL samples, indicating that miRNAs may regulate the expression of other miRNAs and their targets. The findings highlight the importance of miRNA expression in the pathogenesis of CLL and suggest that miRNAs may serve as potential biomarkers for the diagnosis and prognosis of this disease.MicroRNA (miRNA) profiling reveals distinct signatures in B cell chronic lymphocytic leukemia (CLL). This study used a microarray containing hundreds of human precursor and mature miRNA oligonucleotide probes to perform genome-wide expression profiling of miRNAs in CLL samples and normal CD5+ B cells. The results showed significant differences in miRNome expression between CLL samples and normal CD5+ B cells, confirmed by Northern blot and real-time RT-PCR. Two distinct clusters of CLL samples were identified based on the presence or absence of Zap-70 expression, a predictor of early disease progression. Two miRNA signatures were associated with the presence or absence of mutations in the expressed Ig variable-region genes or with deletions at 13q14, respectively. These findings suggest that miRNA expression patterns are relevant to the biological and clinical behavior of CLL. MiRNAs are small, non-coding RNA molecules that regulate gene expression. They are involved in various biological processes, including cell proliferation, cell death, stress resistance, and fat metabolism. The study found that miRNA expression patterns differ between normal and neoplastic cells, and that miRNAs may play a significant role in the pathogenesis of human cancer. The miRNA microarray chip developed in this study allows for the analysis of miRNA expression in various human tissues, revealing distinct miRNA signatures for different tissue types. The study also found that miRNA expression profiles differ between CLL cells and normal CD5+ B cells, with several miRNAs located within fragile sites showing distinct expression patterns. The study further demonstrated that miRNA expression in CLL is associated with clinical and biological factors, such as the levels of ZAP-70 and the presence of mutations in the IgVH genes. The results suggest that miRNA expression profiles have prognostic significance in CLL. Additionally, the study found that miRNA expression is inversely correlated with the levels of Pten protein in CLL samples, indicating that miRNAs may regulate the expression of other miRNAs and their targets. The findings highlight the importance of miRNA expression in the pathogenesis of CLL and suggest that miRNAs may serve as potential biomarkers for the diagnosis and prognosis of this disease.