Behavioral Problems in Fragile X Syndrome: A Review of Clinical Management

Advances on the Mechanisms and Therapeutic Strategies in Non-coding CGG Repeat Expansion Diseases

Non-coding CGG repeat expansions within the 5' untranslated region are implicated in a range of neurological disorders, including fragile X-associated tremor/ataxia syndrome, oculopharyngeal myopathy with leukodystrophy, and oculopharyngodistal myopathy. This review outlined the general characteristics of diseases associated with non-coding CGG repeat expansions, detailing their clinical manifestations and neuroimaging patterns, which often overlap and indicate shared pathophysiological traits. We summarized the underlying molecular mechanisms of these disorders, providing new insights into the roles that DNA, RNA, and toxic proteins play. Understanding these mechanisms is crucial for the development of targeted therapeutic strategies. These strategies include a range of approaches, such as antisense oligonucleotides, RNA interference, genomic DNA editing, small molecule interventions, and other treatments aimed at correcting the dysregulated processes inherent in these disorders. A deeper understanding of the shared mechanisms among non-coding CGG repeat expansion disorders may hold the potential to catalyze the development of innovative therapies, ultimately offering relief to individuals grappling with these debilitating neurological conditions.

Dysregulated COMT Expression in Fragile X Syndrome

Transcriptional and proteomics analyses in human fragile X syndrome (FXS) neurons identified markedly reduced expression of COMT, a key enzyme involved in the metabolism of catecholamines, including dopamine, epinephrine and norepinephrine. FXS is the most common genetic cause of intellectual disability and autism spectrum disorders. COMT encodes for catechol-o-methyltransferase and its association with neuropsychiatric disorders and cognitive function has been extensively studied. We observed a significantly reduced level of COMT in in FXS human neural progenitors and neurons, as well as hippocampal neurons from Fmr1 null mice. We show that deficits in COMT were associated with an altered response in an assay of dopaminergic activity in Fmr1 null mice. These findings demonstrate that loss of FMRP downregulates COMT expression and affects dopamine signaling in FXS, and supports the notion that targeting catecholamine metabolism may be useful in regulating certain neuropsychiatric aspects of FXS.

Prolonged and specific spatial training during adolescence reverses adult hippocampal network impairments in a mouse model of fragile X syndrome

The fragile X syndrome (FXS) is the leading monogenetic cause of cognitive impairment and autism. A hallmark of FXS in patients and the FXS mouse model (Fmr1 KO) is an overabundance of immature appearing dendritic spines in the cortex and hippocampus which is associated with behavioral deficits. Spine analysis in the different hippocampal subregions and at different developmental stages revealed that in adult mice, hippocampal spine pathology occurs specifically in the CA3 subregion, which plays a pivotal role in pattern completion processes important for efficient memory recall from parts of the initial memory stimulus. In line with this synaptic defect we document an impairment in memory recall during partially cued reference memory test in the Morris water maze task. This is accompanied by impaired recruitment of engram cells as well as impaired spine structural plasticity in the CA3 region. In order to promote hippocampal network development adolescent mice were either raised in an enriched environment or subjected to specific hippocampus-dependent spatial training. Intriguingly, only specific spatial training alleviated the cognitive symptoms and the spine phenotype shown in adult Fmr1 KO mice suggesting that specific stimulation of hippocampal networks during development might be used in the future as a therapeutic strategy.

Quality of life of Brazilian families who have children with Fragile X syndrome: a descriptive study

This study aimed to assess the Family Quality of Life (FQoL) of Brazilian families with male children with Fragile X syndrome (FXS). Data from 53 families were collected using forms that included sociodemographic and clinical information, as well as the Beach Center Family Quality of Life Scale, a 5-point Likert scale ranging from "very dissatisfied" (1) to "very satisfied" (5). The mean overall FQoL score was 3.56 ± 0.79; the emotional well-being domain had the lowest score (2.98 ± 1.11) and showed significant differences between the other domains: family interaction (3.81 ± 0.89; p < 0.001), parenting (3.66 ± 0.89; p < 0.001), physical and material well-being (3.48 ± 0.83; p < 0.001), and disability-related support (3.75 ± 0.98; p < 0.001). Physical and material well-being was the second-lowest domain and was statistically different from the family interaction domain (p = 0.013). Lower FQoL satisfaction ratings were found in families with children who had difficulty getting along with people of the same age (t(51) = -3.193, p = 0.002; d = 1.019) and difficulty in living together on a day-to-day basis (t(51) = -3.060, p = 0.004; d = 0.888). These results highlight the importance of proper emotional support for the family, emphasizing the need to provide assistance not only for individuals with FXS but also for other family members. Besides, we advocate for the adoption of public policies that provide financial assistance to families and the implementation of the Brazilian Policy of Comprehensive Care for People with Rare Diseases.

Epilepsy Characteristics in Neurodevelopmental Disorders: Research from Patient Cohorts and Animal Models Focusing on Autism Spectrum Disorder

Epilepsy, a heterogeneous group of brain-related diseases, has continued to significantly burden society and families. Epilepsy comorbid with neurodevelopmental disorders (NDDs) is believed to occur due to multifaceted pathophysiological mechanisms involving disruptions in the excitation and inhibition (E/I) balance impeding widespread functional neuronal circuitry. Although the field has received much attention from the scientific community recently, the research has not yet translated into actionable therapeutics to completely cure epilepsy, particularly those comorbid with NDDs. In this review, we sought to elucidate the basic causes underlying epilepsy as well as those contributing to the association of epilepsy with NDDs. Comprehensive emphasis is put on some key neurodevelopmental genes implicated in epilepsy, such as MeCP2, SYNGAP1, FMR1, SHANK1-3 and TSC1, along with a few others, and the main electrophysiological and behavioral deficits are highlighted. For these genes, the progress made in developing appropriate and valid rodent models to accelerate basic research is also detailed. Further, we discuss the recent development in the therapeutic management of epilepsy and provide a briefing on the challenges and caveats in identifying and testing species-specific epilepsy models.