Cyclin dependent kinase like 5 (CDKL5) deficiency disorder (CDD) is a syndromic autism-spectrum condition with a broad constellation of severe cognitive, sensory-motor and autonomic deficits. Mutations on CDKL5 gene lead to abnormalities of neuronal and synaptic maturation in both CDKL5 mouse mutants and CDD human brains. These abnormalities can be recapitulated by defects in cell-to-cell communication mechanisms, such as for instance those mediated by extracellular vesicles (EVs), lipid-enclosed nanoparticles secreted by all cells, which content reflects the physiological or pathological condition of the releasing cells. Among the molecules carried by EVs, microRNAs (miRNAs) drew much attention since they are directly engaged in the regulation of crucial processes underlying both brain and circuits development/plasticity. We thus tested the hypothesis that CDKL5 can regulate EVs-mediated cell-to-cell communication, and weather the miRNAs contained in EVs derived from neurons lacking-CDKL5 are pathogenic. To this aim, we first added EVs that were isolated from CDKL5-KO cortical neurons on WT neuronal cultures and we found that it produces similar severe synaptic defects as those shown by CDKL5-KO neurons. In contrast, the addition of WT EVs to CDKL5-KO neurons was sufficient to rescue most synaptic defects. Furthermore, given the urgent need to identify reliable and non-invasive molecular biomarkers for CDD, we purified miRNAs from EVs isolated in saliva samples of more than 20 CDD patients and matching controls. Currently, by using miRNomics and bioinformatics approaches, we are analyzing miRNAs identity in CDD patients and neuronal-derived EVs to identify both biomarkers and novel druggable pathways for CDD.