INVESTIGATING THE ROLE OF NOVEL GENES IN NEURODEVELOPMENTAL DISORDERS

Neurodevelopmental disorders (NDDs) are complex and diverse disorders of the developing human brain. Among them, intellectual disability (ID) is a lifelong pathological condition characterized by significant subaverage intellectual/cognitive functioning as well as adaptive functioning due to abnormalities of brain structure and function, whose onset occur before the age of 18. It affects 1–3% of the worldwide population, and no pharmacological therapies are currently available. ID is very heterogeneous in its etiology, being associated with a significant genetic and clinical variability. Some causes of ID have been defined, including genetic disorders, traumatic injuries, and prenatal events such as maternal infection or exposure to alcohol. Despite the common phenotype, the genetic bases are highly heterogeneous and apparently unrelated, and causes of ID remain unknown for up to 60% of all cases. Since the variety of ID makes challenging genetic and clinical diagnosis, in recent years a combined approach of exome sequencing and bioinformatics analysis has identified new ways to understand the causes of ID and help to interpret novel ID-causing genes. The identification of novel genes implicated in NDDs is fundamental to ameliorate diagnosis and treatment. Here, we have combined exome sequencing together with in silico, in vitro and in vivo experimental models to identify novel NDDs causative genes. First, we found out a novel heterozygous variant in Semaphorin 3E (SEMA3E) gene in a patient affected by severe ID and cognitive regression. We demonstrated that the identified mutation is causative of a complete loss of function of the Sema3E protein. Therefore, our in vitro and in vivo studies in mice might suggest that the mutation would possibly be involved in brain development and would explain, at least in part, ID pathogenesis. Further studies are needed to better understand the role of this family of genes in the susceptibility to NDDs, and the identification of additional mutations in patients affected by similar disorders will allow us to analyze the clinical relevance of SEMA3E. Moreover, we identified two brothers affected by an unrecognized genetic syndrome, comprising ID, and facial dysmorphisms, carrying mutation in Rhotekin (RTKN) and Natural Killer cell Triggering Receptor (NKTR). Our experiments have been important to reveal a novel role for two not well characterized genes in brain and head development. In particular, we demonstrated that RTKN has a central role in controlling cytoskeletal dynamics via Cofilin, by remodeling actin filaments. Besides, we elucidated a further role of NKTR as a novel RNA splicing protein downstream of SOX9, which is essential for craniofacial development and causing, if mutated, a novel craniofacial spliceosomopathy/neurocristopathy. The wealth of information deriving from this project will significantly increase our knowledge on RTKN and NKTR physiological role, which has been hitherto largely undescribed, and will validate these genes as novel causative gene of developmental syndromes. This project also provided evidence that the combined access to mutational screenings of patients with the application of in silico, in vitro and in vivo experimental models is effective in the discovery of novel genes implicated in complex disorders such as NDDs. Such information will be vital to ameliorate diagnosis and therapeutic intervention of disorders still largely idiopathic and being recognized as a leading cause of morbidity in children, causing great suffering for patients and their families and large costs for society.