The development of language is the most important conquest of human cognition. What is the relation between preverbal communication and language? From a developmental point of view, children develop language from preexisting skills, both mental and social, as joint attention. Joint attention is the function by which two individual establish a mutual ocular contact. The sharedness of a common attentional focus is the main stage of use of pointing, knowledge of communicative intentions and the development of linguistic reference. Normally, the typical-developing children use pointing in order not just to interact with social partners, but also to lead and change the other's attentional behaviour. It has been saw than children with Down and Williams Syndrome show several problems in joint attention skills as pointing and the comprehension of communicative intentions. I will propose to use those pathologies in order to show how the sense of agency understanding and the shared intentionality are the core of crossing from preverbal to linguistic communication.