It has been recently suggested to approach schizophrenia as a neurodevelopmental disorder with psychosis as a late, potentially preventable stage of the illness. While efforts have been conducted to improve our knowledge on distal and proximal risk factors, the researches conducted leave many unanswered questions concerning: 1) the interaction between genes and environment and 2) the role played by specific neurodevelopmental phases. Therefore, we decided to concentrate our research efforts on two specific populations. The 22q11.2 deletion syndrome population can contribute in providing an answer to the first pending question, while the child and adolescent population can help us to provide an answer to the second pending question. This thesis starts with a comprehensive review of these topics. The second part of the thesis is based on a compilation of a selection of my publications. Implications are explored, in terms of clinical practice and treatments strategies.