Autism Spectrum Disorders (ASD) are characterized by social and communicational impairments, along with altered patterns of behaviour. The aetiology of ASD is still unclear, despite the identification of some genetic and environmental factors linked to the disorder. New de novo genomic variants have been identified in ASD cases, but their functional implication in ASD development is still to be reported. In this communication, we address the generation of in vitro and in vivo models to study the implication of de novo mutations linked to ASD in neurodevelopment, with the final goal of improving our understanding of the molecular bases of the disorder and the genetic counselling offered to the families, as well as proposing new therapeutical targets. As an in vitro model, we selected human induced pluripotent stem cells (hiPSCs), due to their differentiation capability into neuronal-like cell lines. CRISPR/Cas9 was applied to alter the function of the genes of interest, after which the mutated cell lines were differentiated to 2D neuronal cultures and whole-brain organoids. The obtained in vitro models were analysed at several time points using immunostaining, qPCR, calcium imaging and scRNAseq, to identify how the mutations of interest alter neurodevelopment and neural function. As an in vivo model, we generated zebrafish mutant lines using CRISPR/Cas9 to study the impact of the mutations of interest in the whole organism. Homozygous and heterozygous individuals were characterized and compared to wild-type animals to identify morphological, transcriptional, and behavioural alterations associated to the mutation of genes linked to ASD.