Rett syndrome (RTT) is a rare disease and one of the most abundant causes for intellectual disa-bilities in females. Single mutations in the gene coding for methyl-CpG-binding protein 2 (MECP2), are responsible for the disease. MeCP2 regulates gene expression as a transcriptional regulator as well as through epigenetic imprinting and chromatin condensation. Consequently, numerous biological pathways on multiple levels are influenced however, the exact molecular pathways from genotype to phenotype are currently not fully elucidated. Treatment of RTT is purely symptomatic where no curative options for RTT have yet to reach the clinic. The paucity of this is mainly due to an incomplete understanding of the underlying pathophysiology of the dis-order with no clinically useful common disease drivers, biomarkers or therapeutic targets being identified. With the premise of identifying universal and robust disease drivers and therapeutic targets, here we interrogated a range of RTT transcriptomic studies spanning different species, models and MECP2 mutations. A meta-analysis using RNA sequencing data from brains of RTT mouse models human post-mortem brain tissue and patient-derived induced pluripotent stem cells (iPSC) neurons was performed using Weighted Gene Correlation Network Analysis (WGC-NA). This study identified a module of genes common to all datasets with the following ten hub genes driving the expression ATRX, ADCY7, ADCY9, SOD1, CACNA1A, PLCG1, CCT5, RPS9, BDNF and MECP2. Here we discuss the potential benefits of these genes as therapeutic targets.

Objective: Rett syndrome (RTT) is an X-linked neurodevelopmental disorder caused by mutations in MeCP2, a transcription factor. MeCP2 mutations cause abnormal expression of downstream genes and eventually lead to brain dysfunction. The role of MeCP2 in brain neural development remains unclear. To further elucidate this role, a MeCP2-null rat model was created with the CRISPR/cas9 system. Method: A MeCP2-cas9 vector was constructed and then microinjected into fertilized rat ova in vitro. Two mutations by CRISPR/cas9 were confirmed to cause deletions in exon 2 of MeCP2 via DNA sequencing, and protein expression was measured by Western blotting. Transcriptome data for three brain tissues, the cerebellum, cerebral cortex and hippocampus, were obtained via next-generation sequencing. Results: MeCP2-null rats were successfully obtained, and preliminary analysis showed that the MeCP2-null rats exhibited motor dysfunction and anxious and depressed behaviour. In addition, differentially expressed genes (DEGs) were identified in the three MeCP2-null brain tissues compared to wild-type rat brain tissues. In the rat cerebellum, 388 downregulated DEGs were mainly involved in the calcium ion signalling pathway and the PI3K-Akt signalling pathway. In the cerebral cortex, 386 upregulated DEGs were primarily involved in intracellular signal transduction, protein phosphorylation and the MAPK signalling pathway. In the hippocampus, the DEGs were related to the MAPK signalling pathway. Conclusion: We constructed a MeCP2-null rat model with unique features with CRISPR/cas9 technology to study RTT and analysed DEGs in three rat brain tissues to highlight potential targets for the development of new medicines.

1) This study describes the good evolution of a 6-year-old girl genetically diagnosed with Rett syndrome (RTT), after having been treated with IGF-1, MT (MT), blackcurrant extracts (BC), and rehabilitation during 6 months. 2) The patient stopped her normal development from the first year of age. The patient showed low weight and height and met the main criteria for typical RTT. Curiously, there was pubic hair (Tanner II), very high plasma testosterone, despite low gonadotropins. No adrenal enzymatic deficits existed, and ultrasound abdominal studies were normal. Treatment consisted in IGF-1 (0.04 mg/kg/day, 5/week, sc) during 3-months and then 15-days resting, MT (50 mg/day, orally, uninterruptedly) and neurorehabilitation. The new blood tests were absolutely normal and the pubic hair disappeared. Then, a new treatment with IGF-1, MT, and BC started for another 3 months. After it, pubic Tanner stage increased to III, without a known cause. 3) The treatment followed led to clear improvements in most of the initial impairments, perhaps because of the effect of IGF-I, the antioxidant effects of MT and BC, and the increase in cyclic-glycine-proline (cGP) after BC administration. 4) A continuous treatment with IGF-1, MT and BC may recover most of the neurologic disabilities that occur in RTT.