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Rett syndrome is a rare, genetic neurodevelopmental disorder. Trofinetide is a synthetic analog of glycine–proline–glutamate, the N-terminal tripeptide of the insulin-like growth factor 1 protein, and has demonstrated clinical benefit in phase 2 studies in Rett syndrome. In this phase 3 study ( https://clinicaltrials.gov identifier NCT04181723 ), females with Rett syndrome received twice-daily oral trofinetide ( n  = 93) or placebo ( n  = 94) for 12 weeks. For the coprimary efficacy endpoints, least squares mean (LSM) change from baseline to week 12 in the Rett Syndrome Behaviour Questionnaire for trofinetide versus placebo was −4.9 versus −1.7 ( P  = 0.0175; Cohen’s d effect size, 0.37), and LSM Clinical Global Impression–Improvement at week 12 was 3.5 versus 3.8 ( P  = 0.0030; effect size, 0.47). For the key secondary efficacy endpoint, LSM change from baseline to week 12 in the Communication and Symbolic Behavior Scales Developmental Profile Infant–Toddler Checklist Social Composite score was −0.1 versus −1.1 ( P  = 0.0064; effect size, 0.43). Common treatment-emergent adverse events included diarrhea (80.6% for trofinetide versus 19.1% for placebo), which was mostly mild to moderate in severity. Significant improvement for trofinetide compared with placebo was observed for the coprimary efficacy endpoints, suggesting that trofinetide provides benefit in treating the core symptoms of Rett syndrome. Results from the LAVENDER phase 3 study demonstrate that trofinetide, a synthetic analog of glycine–proline–glutamate, provides significant therapeutic benefits in the core symptoms of Rett syndrome

This systematic review and thematic analysis critically evaluated gene therapy trials in amyotrophic lateral sclerosis, haemoglobinopathies, immunodeficiencies, leukodystrophies, lysosomal storage disorders and retinal dystrophies and extrapolated the key clinical findings to individuals with Rett syndrome (RTT). The PRISMA guidelines were used to search six databases during the last decade, followed by a thematic analysis to identify the emerging themes. Thematic analysis across the different disorders revealed four themes: (I) Therapeutic time window of gene therapy; (II) Administration and dosing strategies for gene therapy; (III) Methods of gene therapeutics and (IV) Future areas of clinical interest. Our synthesis of information has further enriched the current clinical evidence base and can assist in optimising gene therapy and gene editing studies in individuals with RTT, but it would also benefit when applied to other disorders. The findings suggest that gene therapies have better outcomes when the brain is not the primary target. Across different disorders, early intervention appears to be more critical, and targeting the pre-symptomatic stage might prevent symptom pathology. Intervention at later stages of disease progression may benefit by helping to clinically stabilise patients and preventing disease-related symptoms from worsening. If gene therapy or editing has the desired outcome, older patients would need concerted rehabilitation efforts to reverse their impairments. The timing of intervention and the administration route would be critical parameters for successful outcomes of gene therapy/editing trials in individuals with RTT. Current approaches also need to overcome the challenges of MeCP2 dosing, genotoxicity, transduction efficiencies and biodistribution.

Alzheimer's disease (AD) and Rett syndrome (Rett) share overlapping genetic and molecular features. NA-831, a small-molecule drug, promotes neuroprotection and neurogenesis for AD treatment. NA-921, an analog of NA-831, modulates MeCP2 expression and function for Rett treatment. NA-831: A randomized clinical trial was conducted in 112 participants with mild to moderate AD. Subjects were randomized to receive either NA-831 or placebo. Patients with mild cognitive impairment (MCI) received 10 mg/day of NA-831 or placebo orally, while patients with mild to moderate AD received 30 mg/day. Subjects with MCI to meet the NIA-AA core clinical criteria, CDR score of 0.5 and a Memory Box score of 0.5 or greater at Screening and Baseline and an MMSE ≥22. Subjects with mild to moderate AD had MMSE scores between 17-21. (ClinicalTrials.gov ID: NCT03538522) NA-921: A randomized, double-blind, placebo-controlled Phase 2/3 study evaluated NA-921 (Bionetide) in girls and women with Rett syndrome. (ClinicalTrials.gov ID: NCT06849973) RESULT: NA-831: After 24 weeks of treatment, patients with mild to moderate AD receiving NA-831 showed a significant improvement in ADAS-Cog-13 scores, with an average change of 4.1 compared to placebo (p = 0.001; ITT). CIBIC-Plus results showed improvement in 78% of patients (p = 0.01; ITT). NA-831 was well tolerated at 30 mg/day, with no serious adverse events observed, suggesting a safer oral alternative to current AD treatments. NA-921: NA-921 significantly improved outcomes in Rett syndrome. On the Rett Syndrome Behavior Questionnaire (RSBQ), the least squares mean change at week 12 was -5.5 for NA-921 vs. -1.6 for placebo (p = 0.001; n = 86 vs. 87). For Clinical Global Impression-Improvement (CGI-I), scores at week 12 were 3.60 (NA-921) vs. 3.83 (placebo), with a significant effect size of 0.42 (p = 0.0020). NA-921 is a potential treatment for Rett Syndrome with fewer side effects and improved patient retention rates. These findings support a potential mechanistic link between Alzheimer's disease and Rett syndrome. Both NA-831 and NA-921 show promise as novel, well-tolerated therapeutic agents. Further studies are warranted to validate these results and deepen our understanding of the shared molecular pathways between this neurodegenerative and neurodevelopmental disorder.

Dysfunctions in GABAergic inhibitory neural transmission occur in neuronal injuries and neurological disorders. The potassium–chloride cotransporter 2 (KCC2, SLC12A5) is a key modulator of inhibitory GABAergic inputs in healthy adult neurons, as its chloride (Cl−) extruding activity underlies the hyperpolarizing reversal potential for GABAA receptor Cl− currents (EGABA). Manipulation of KCC2 levels or activity improve symptoms associated with epilepsy and neuropathy. Recent works have now indicated that pharmacological enhancement of KCC2 function could reactivate dormant relay circuits in an injured mouse’s spinal cord, leading to functional recovery and the attenuation of neuronal abnormality and disease phenotype associated with a mouse model of Rett syndrome (RTT). KCC2 interacts with Huntingtin and is downregulated in Huntington’s disease (HD), which contributed to GABAergic excitation and memory deficits in the R6/2 mouse HD model. Here, these recent advances are highlighted, which attest to KCC2’s growing potential as a therapeutic target for neuropathological conditions resulting from dysfunctional inhibitory input.

Nutritional supplements are traditionally employed for overall health and for managing some health conditions, although controversies are found concerning the role of antioxidants‐mediated benefits in vivo. Consistently with its critical role in systemic redox buffering, red blood cell (RBC) is recognized as a biologically relevant target to investigate the effects of oxidative stress. In RBC, reduction of the ATP levels and adenylate energy charge brings to disturbance in intracellular redox status. In the present work, several popular antioxidant supplements were orally administrated to healthy adults and examined for their ability to induce changes on the energy metabolism and oxidative status in RBC. Fifteen volunteers (3 per group) were treated for 30 days per os with epigallocatechin gallate (EGCG) (1 g green tea extract containing 50% EGCG), resveratrol (325 mg), coenzyme Q10 (CoQ10) (300 mg), vitamin C (1 g), and vitamin E (400 U.I.). Changes in the cellular levels of high-energy compounds (i.e., ATP and its catabolites, NAD and GTP), GSH, GSSG, and malondialdehyde (MDA) were simultaneously analyzed by ion-pairing HPLC. Response to oxidative stress was further investigated through the oxygen radical absorptive capacity (ORAC) assay. According to our experimental approach, (i) CoQ10 appeared to be the most effective antioxidant inducing a high increase in ATP/ADP, ATP/AMP, GSH/GSSG ratio and ORAC value and, in turn, a reduction of NAD concentration, (ii) EGCG modestly modulated the intracellular energy charge potential, while (iii) Vitamin E, vitamin C, and resveratrol exhibited very weak effects. Given that, the antioxidant potential of CoQ10 was additionally assessed in a pilot study which considered individuals suffering from Rett syndrome (RTT), a severe X-linked neuro-developmental disorder in which RBC oxidative damages provide biological markers for redox imbalance and chronic hypoxemia. RTT patients (n = 11), with the typical clinical form, were supplemented for 12 months with CoQ10 (300 mg, once daily). Level of lipid peroxidation (MDA production) and energy state of RBCs were analyzed at 2 and 12 months. Our data suggest that CoQ10 may significantly attenuate the oxidative stress-induced damage in RTT erythrocytes.

Analysis of the minimal functional unit for MeCP2 protein shows that its function is to recruit the NCoR/SMRT co-repressor complex to methylated sites on chromatin, which may have use in designing strategies for gene therapy of Rett syndrome. MeCP2 to the Rett-scue Rett syndrome is a neurological disorder caused by mutations in the MECP2 gene, which tend to be clustered in two discrete regions of the protein (MeCP2). In this report, the authors parse the minimal form of MeCP2 that is required to retain its functionality, and interrogate which of its many proposed roles is relevant for Rett syndrome progression. The identification of a minimal functional unit for MeCP2 could be helpful in the design of therapeutic strategies for gene therapy for Rett syndrome. Heterozygous mutations in the X-linked MECP2 gene cause the neurological disorder Rett syndrome 1 . The methyl-CpG-binding protein 2 (MeCP2) protein is an epigenetic reader whose binding to chromatin primarily depends on 5-methylcytosine 2 , 3 . Functionally, MeCP2 has been implicated in several cellular processes on the basis of its reported interaction with more than 40 binding partners 4 , including transcriptional co-repressors (for example, the NCoR/SMRT complex 5 ), transcriptional activators 6 , RNA 7 , chromatin remodellers 8 , 9 , microRNA-processing proteins 10 and splicing factors 11 . Accordingly, MeCP2 has been cast as a multi-functional hub that integrates diverse processes that are essential in mature neurons 12 . At odds with the concept of broad functionality, missense mutations that cause Rett syndrome are concentrated in two discrete clusters coinciding with interaction sites for partner macromolecules: the methyl-CpG binding domain 13 and the NCoR/SMRT interaction domain 5 . Here we test the hypothesis that the single dominant function of MeCP2 is to physically connect DNA with the NCoR/SMRT complex, by removing almost all amino-acid sequences except the methyl-CpG binding and NCoR/SMRT interaction domains. We find that mice expressing truncated MeCP2 lacking both the N- and C-terminal regions (approximately half of the native protein) are phenotypically near-normal; and those expressing a minimal MeCP2 additionally lacking a central domain survive for over one year with only mild symptoms. This minimal protein is able to prevent or reverse neurological symptoms when introduced into MeCP2-deficient mice by genetic activation or virus-mediated delivery to the brain. Thus, despite evolutionary conservation of the entire MeCP2 protein sequence, the DNA and co-repressor binding domains alone are sufficient to avoid Rett syndrome-like defects and may therefore have therapeutic utility.

Background Preclinical studies and anecdotal case reports support the potential therapeutic benefit of low-dose oral ketamine as a treatment of clinical symptoms in Rett syndrome (RTT); however, no controlled studies have been conducted in RTT to evaluate safety, tolerability and efficacy. Design This was a sequentially initiated, dose-escalating cohort, placebo-controlled, double blind, randomized sequence, cross-over study of oral ketamine in 6–12-year-old girls with RTT to evaluate short-term safety and tolerability and explore efficacy. Methods Participants were randomized to either five days treatment with oral ketamine or matched placebo, followed by a nine-day wash-out period and then crossed-over to the opposite treatment. Ketamine was dosed twice daily at 0.75 mg/kg/dose (Cohort 1) or 1.5 mg/kg/dose (Cohort 2). An independent safety monitoring committee evaluated safety and approved proceeding to the next dose cohort. Caregivers, participants, outcome assessors, and study staff except pharmacists were blinded to allocation. The primary endpoint was safety and tolerability. Exploratory efficacy endpoints included change in clinician- and caregiver-rated measures of RTT features, brain activity on electroencephalography, and wearable biosensors to measure respiration, heart rate, sleep, and activity. Results Twenty-three participants enrolled (11 in Cohort 1, 12 in Cohort 2) from 3/12/2019–11/22/2021. One participant was excluded from analysis due to not meeting inclusion criteria on blinded review prior to analysis. One participant was withdrawn from the study due to an adverse event (vomiting) after the first dose of ketamine. Although planned for four dose cohorts, the trial was stopped after Cohort 2 due to enrollment challenges associated with the COVID-19 pandemic. Ketamine was safe and tolerated in both cohorts, with 1 related treatment emergent adverse event of vomiting. No difference was observed in efficacy between ketamine and placebo. Electroencephalography showed the expected increase in high frequency power with ketamine. Conclusions Short-term, low-dose oral ketamine was safe and well tolerated in girls with RTT. No clinical efficacy of ketamine in treating symptoms of RTT was observed with 5 days of treatment, despite electroencephalography evidence of ketamine target engagement during the first dose. Further studies are needed to evaluate safety and efficacy of higher dose and longer exposure to ketamine in RTT. Trial registration Registered at clinicaltrials.gov NCT03633058.

Deep brain stimulation (DBS) of the fimbria–fornix—a region that provides input to the hippocampus—is shown to restore hippocampus-dependent memory and hippocampal long-term potentiation and neurogenesis in a mouse model of Rett syndrome, suggesting that DBS, which is already used in the treatment of several neurological conditions, could be a viable approach to mitigating cognitive impairment in Rett syndrome and other disorders of childhood intellectual disability. Deep brain stimulation in Rett syndrome Rett syndrome is a genetic disorder that causes profound intellectual disability and other impairments. Huda Zoghbi and colleagues now show that in a mouse model of the disorder, a two-week course of daily deep-brain stimulation of the fimbria-fornix — part of the brain that provides input to the hippocampus — restored hippocampal-dependent memory when tested three weeks after the end of the treatment. It also restored hippocampal long-term potentiation and neurogenesis. These findings indicate that deep-brain stimulation, which is already used in the treatment of motor diseases such as Parkinson's disease and dystonia, could be a viable approach to mitigating cognitive impairment in Rett syndrome and other disorders of childhood intellectual disability. Deep brain stimulation (DBS) has improved the prospects for many individuals with diseases affecting motor control, and recently it has shown promise for improving cognitive function as well. Several studies in individuals with Alzheimer disease and in amnesic rats have demonstrated that DBS targeted to the fimbria–fornix 1 , 2 , 3 , the region that appears to regulate hippocampal activity, can mitigate defects in hippocampus-dependent memory 3 , 4 , 5 . Despite these promising results, DBS has not been tested for its ability to improve cognition in any childhood intellectual disability disorder. Such disorders are a pressing concern: they affect as much as 3% of the population and involve hundreds of different genes. We proposed that stimulating the neural circuits that underlie learning and memory might provide a more promising route to treating these otherwise intractable disorders than seeking to adjust levels of one molecule at a time. We therefore studied the effects of forniceal DBS in a well-characterized mouse model of Rett syndrome (RTT), which is a leading cause of intellectual disability in females. Caused by mutations that impair the function of MeCP2 (ref. 6 ), RTT appears by the second year of life in humans, causing profound impairment in cognitive, motor and social skills, along with an array of neurological features 7 . RTT mice, which reproduce the broad phenotype of this disorder, also show clear deficits in hippocampus-dependent learning and memory and hippocampal synaptic plasticity 8 , 9 , 10 , 11 . Here we show that forniceal DBS in RTT mice rescues contextual fear memory as well as spatial learning and memory. In parallel, forniceal DBS restores in vivo hippocampal long-term potentiation and hippocampal neurogenesis. These results indicate that forniceal DBS might mitigate cognitive dysfunction in RTT.

Transplanting bone marrow from wild-type mice into MECP2-lacking mice results in wild-type microglial engraftment, extends lifespan and reduces symptoms of disease such as breathing and locomotor abnormalities, implicating microglia in the pathophysiology of Rett syndrome. Marrow implants in Rett syndrome The X-linked autism spectrum disorder known as Rett syndrome is predominantly linked to mutations in the MECP2 gene. It is typically associated with neuronal dysfunction, almost exclusively in girls, but new evidence suggests that restoring MECP2 function in other cell types may also arrest disease development. Here, the authors show in a mouse model that transplanting bone marrow from wild-type mice into mice lacking Mecp2 results in an invasion of donor-derived microglial cells into the brain, accompanied by increased lifespan and reduced signs of disease, including improved breathing and locomotion. The donor cells expressed normal MECP2 and high levels of the neurotrophic factor IGF-1. These results point to a crucial role for microglia in Rett syndrome, and open the possibility that bone-marrow implants might be of therapeutic benefit. Rett syndrome is an X-linked autism spectrum disorder. The disease is characterized in most cases by mutation of the MECP2 gene, which encodes a methyl-CpG-binding protein 1 , 2 , 3 , 4 , 5 . Although MECP2 is expressed in many tissues, the disease is generally attributed to a primary neuronal dysfunction 6 . However, as shown recently, glia, specifically astrocytes, also contribute to Rett pathophysiology. Here we examine the role of another form of glia, microglia, in a murine model of Rett syndrome. Transplantation of wild-type bone marrow into irradiation-conditioned Mecp2 -null hosts resulted in engraftment of brain parenchyma by bone-marrow-derived myeloid cells of microglial phenotype, and arrest of disease development. However, when cranial irradiation was blocked by lead shield, and microglial engraftment was prevented, disease was not arrested. Similarly, targeted expression of MECP2 in myeloid cells, driven by Lysm cre on an Mecp2 -null background, markedly attenuated disease symptoms. Thus, through multiple approaches, wild-type Mecp2 -expressing microglia within the context of an Mecp2 -null male mouse arrested numerous facets of disease pathology: lifespan was increased, breathing patterns were normalized, apnoeas were reduced, body weight was increased to near that of wild type, and locomotor activity was improved. Mecp2 +/− females also showed significant improvements as a result of wild-type microglial engraftment. These benefits mediated by wild-type microglia, however, were diminished when phagocytic activity was inhibited pharmacologically by using annexin V to block phosphatydilserine residues on apoptotic targets, thus preventing recognition and engulfment by tissue-resident phagocytes. These results suggest the importance of microglial phagocytic activity in Rett syndrome. Our data implicate microglia as major players in the pathophysiology of this devastating disorder, and suggest that bone marrow transplantation might offer a feasible therapeutic approach for it.

Rett syndrome is a neurological disease due to loss-of-function mutations in the transcription factor, Methyl CpG binding protein 2 (MECP2). Because overexpression of endogenous MECP2 also causes disease, we have exploited a targeted RNA-editing approach to repair patient mutations where levels of MECP2 protein will never exceed endogenous levels. Here, we have constructed adeno-associated viruses coexpressing a bioengineered wild-type ADAR2 catalytic domain (Editasewt) and either Mecp2-targeting or nontargeting gfp RNA guides. The viruses are introduced systemically into male mice containing a guanosine to adenosine mutation that eliminates MeCP2 protein and causes classic Rett syndrome in humans. We find that in the mutant mice injected with the Mecp2-targeting virus, the brainstem exhibits the highest RNA-editing frequency compared to other brain regions. The efficiency is sufficient to rescue MeCP2 expression and function in the brainstem of mice expressing the Mecp2-targeting virus. Correspondingly, we find that abnormal Rett-like respiratory patterns are alleviated, and survival is prolonged, compared to mice injected with the control gfp guide virus. The levels of RNA editing among most brain regions corresponds to the distribution of guide RNA rather than Editasewt. Our results provide evidence that a targeted RNA-editing approach can alleviate a hallmark symptom in a mouse model of human disease.