['To evaluate the association between the presence of phosphoinositide-phospholipase C beta1 (PI-PLCbeta1) mono-allelic deletion with the clinical outcome of myelodysplastic syndromes (MDS) patients.', 'PI-PLCbeta1, PI-PLCbeta4, and PI-PLCgamma1 cytogenetic investigations were performed on 80 newly diagnosed MDS patients (18 low risk, 26 intermediate 1, 18 intermediate 2, 18 high risk) comparing the results with the clinical outcome of the patients. Moreover, fluorescent in situ hybridization results were validated by real-time polymerase chain reaction (PCR). Finally, PI-PLCbeta1 gene and protein expression were assessed by both real-time PCR and immunocytochemical experiments.', 'Collectively, 35 (43.75%) of 80 of the MDS patients showed a specific mono-allelic deletion of PI-PLCbeta1. Kaplan-Meier analysis revealed a significant association (P < .0001) between the PI-PLCbeta1 mono-allelic deletion and a higher risk of evolution into acute myeloid leukemia (AML), since 23 of 35 MDS patients (65.7%) bearing the PI-PLCbeta1 mono-allelic deletion evolved into AML. Even in multivariate analysis, the PI-PLCbeta1 mono-allelic deletion retained a higher significance, with a P < .001, as a prognostic factor of evolution into AML (odds ratio [OR] 1.83; 95% CI, 2.26 to 17.24; P = .00045). Finally, PI-PLCbeta1 deletion was related to an altered gene and protein expression.'] Is phosphoinositide-phospholipase C beta1 mono-allelic deletion associated with myelodysplastic syndromes evolution into acute myeloid leukemia?