MOLECULAR STUDY OF CHROMATINOPATHIES: THE CASE OF RUBINSTEIN-TAYBI AND RETT SYNDROMES

Background: Chromatinopathies are defined as a group of disorders displaying mutations in genes of the epigenetic apparatus and sharing clinical features such as intellectual disability and abnormal growth. Among them, Rubinstein-Taybi syndrome (RSTS) is characterized by CBP/p300 lysin-acetyltransferases deficit, while classic form of Rett syndrome (RTT) is caused by mutations in the reader MECP2. Both disorders show neurodevelopmental defects and 10 to 30% of patients remains without a molecular diagnosis. Methods: In this work, we aim at deepening molecular aspects involving RSTS and RTT etiology and RSTS possible epigenetic treatments. Indeed, we tested exogenous histone deacetylase inhibitors (HDACi) in in vitro cellular models (lymphoblastoid cell lines derived from patients and healthy donors) and on a Drosophila melanogaster model of RSTS (nej) and wild type flies (yw), performing acetylation and viability assays and flies embryos immunostaining respectively. In parallel, we investigated endogenous HDACi in RSTS patients and in fruit flies models, assessing their microbiota. In addition, we applied whole exome sequencing (WES) analysis to RSTS and RTT-like probands negative for mutations in known associated genes and we then characterized two identified variants by genome editing techniques and functional analysis. Results: In RSTS studies, we observed that patients gut microbiota is significantly depleted in butyrate-producing bacteria and we demonstrate that the effects of the HDACi butyrate, as well as the differences in microbiota composition, are conserved in nej flies. From WES study, we found in one RSTS and three RTT-like patients unreported variants in HDAC2, and NBEA, DYNC1H1 and SLC35F1 genes respectively, whose role is currently under investigation through in vitro models. Conclusions: The study on microbiota composition could pave the way for novel therapeutic interventions for RSTS, while the identification of new RSTS and RTT genes could expand the genotype-phenotype correlation for these chromatinopathies, and characterization of new candidate genes could give insights into pathogenesis of these disorders.