Clinical, molecular, and pharmacological aspects of FMR1 related disorders

Effects of Fmr1 Gene Mutations on Sex Differences in Autism-Like Behavior and Dendritic Spine Development in Mice and Transcriptomic Studies

Fragile X syndrome (FXS) is the most common single gene disorder contributing to autism spectrum disorder (ASD). Although significant sex differences are observed in FXS, few studies have focused on the phenotypic characteristics as well as the differences in brain pathological changes and gene expression in FXS by sex. Therefore, we analyzed sex differences in autism-like behavior and dendritic spine development in two-month-old male and female Fmr1 KO and C57 mice and evaluated the mechanisms at transcriptome level. Results suggest that Fmr1 KO mice display sex differences in autism-like behavior and dendritic spine density. Compared to females, male had more severe effects on anxiety, repetitive stereotype-like behaviors, and socializing, with higher dendritic spine density. Furthermore, two male-biased and five female-biased expressed genes were screened based on KEGG pathway enrichment and protein-protein interaction (PPI) analyses. In conclusion, our findings show mutations in the Fmr1 gene lead to aberrant expression of related genes and affect the sex-differentiated behavioral phenotypes of Fmr1 KO mice by affecting brain development and functional architecture, and suggest future studies should focus on including female subjects to comprehensively reflect the differentiation of FXS in both sexes and develop more precise and effective therapeutic strategies.

Diagnostic value of molecular approach in screening for fragile X premutation cases

BACKGROUND

Fragile X syndrome (FXS) is the most common form of inherited intellectual disability, caused by CGG-repeats expansion (> 200 repeats). Premutation alleles (PM) (55-200 CGG repeats) are associated with tremor ataxia syndrome (FXTAS), fragile X-associated primary ovarian insufficiency (FXPOI), and autistic problems.

AIM

To screen the frequency of premutation carriers using molecular diagnostic assays, in a cohort of Egyptian males with suspected clinical features of (FXS) checking for the presence of premutation alleles.

METHODS

The current study comprised 192 Egyptian male children, 92 participants presented with intellectual disability, delayed language development, autistic-like features, behavioral difficulties, anxiety, seizures, and depression compared to 100 healthy males. All cases were subjected to clinical and neuroimaging assessments, when indicated as well as molecular analysis using methylation-specific PCR (MS-PCR) and quantitative real-time PCR (qRT-PCR).

RESULTS

Thirty-four premutation carriers out of 92 Egyptian males (37%) of CGG repeats (55 to 200) were illustrated with elevated FMR1 mRNA expression level (p-value < 0.001). Additionally, 2 intermediate (IM) cases (0.03%) (45-55 CGG repeats) showed poor increase in expression level (p-value = 0.02838) plus 6 full mutation (FM) patients (0.07%) with (> 200 CGG repeats) (p-value < 0.001) resulted in FMR1 gene silence.

CONCLUSION

Molecular diagnostic assay including (MS-PCR) and (qRT-PCR) proved to be a sensitive and rapid screening tool for the detection of premutation cases. Furthermore, the presence of positive correlation between FMR1 mRNA expression levels with CGG repeats in premutation cases could serve as a potential diagnostic marker. Application of these diagnostic tools on larger number clinically suspected cases is recommended.

The Use of Peptides in the Treatment of Fragile X Syndrome: Challenges and Opportunities

Fragile X Syndrome (FXS) is the most frequent cause of inherited intellectual disabilities and autism spectrum disorders, characterized by cognitive deficits and autistic behaviors. The silencing of the Fmr1 gene and consequent lack of FMRP protein, is the major contribution to FXS pathophysiology. FMRP is an RNA binding protein involved in the maturation and plasticity of synapses and its absence culminates in a range of morphological, synaptic and behavioral phenotypes. Currently, there are no approved medications for the treatment of FXS, with the approaches under study being fairly specific and unsatisfying in human trials. Here we propose peptides/peptidomimetics as candidates in the pharmacotherapy of FXS; in the last years this class of molecules has catalyzed the attention of pharmaceutical research, being highly selective and well-tolerated. Thanks to their ability to target protein-protein interactions (PPIs), they are already being tested for a wide range of diseases, including cancer, diabetes, inflammation, Alzheimer's disease, but this approach has never been applied to FXS. As FXS is at the forefront of efforts to develop new drugs and approaches, we discuss opportunities, challenges and potential issues of peptides/peptidomimetics in FXS drug design and development.

CRISPR/dCas9 as a Therapeutic Approach for Neurodevelopmental Disorders: Innovations and Limitations Compared to Traditional Strategies

Brain development is a complex process that requires a series of precise and coordinated events to take place. When alterations in some of those events occur, neurodevelopmental disorders (NDDs) may appear, with their characteristic symptoms, including cognitive, social motor deficits, and epilepsy. While pharmacologic treatments have been the only therapeutic options for many years, more recently the research is turning to the direct removal of the underlying genetic cause of each specific NDD. This is possible thanks to the increased knowledge of genetic basis of those diseases and the enormous advances in genome-editing tools. Together with clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9-based strategies, there is a great development also of nuclease defective Cas9 (dCas9) tools that, with an extreme flexibility, allow the recruitment of specific protein functions to the desired genomic sites. In this work, we review dCas9-based tools and discuss all the published applications in the setting of therapeutic approaches for NDDs at the preclinical level. In particular, dCas9-based therapeutic strategies for Dravet syndrome, transcallosal dysconnectivity caused by mutations in C11orf46 gene, and Fragile X syndrome are presented and discussed. A direct comparison with other possible therapeutic strategies, such as classic gene replacement or CRISPR/Cas9-based strategies, is provided. We also highlight not only those aspects that constitute a clear advantage compared to previous strategies but also the main technical hurdles related to their applications that need to be overcome.

Rescue of Fragile X Syndrome Neurons by DNA Methylation Editing of the FMR1 Gene

Fragile X syndrome (FXS), the most common genetic form of intellectual disability in males, is caused by silencing of the FMR1 gene associated with hypermethylation of the CGG expansion mutation in the 5' UTR of FMR1 in FXS patients. Here, we applied recently developed DNA methylation editing tools to reverse this hypermethylation event. Targeted demethylation of the CGG expansion by dCas9-Tet1/single guide RNA (sgRNA) switched the heterochromatin status of the upstream FMR1 promoter to an active chromatin state, restoring a persistent expression of FMR1 in FXS iPSCs. Neurons derived from methylation-edited FXS iPSCs rescued the electrophysiological abnormalities and restored a wild-type phenotype upon the mutant neurons. FMR1 expression in edited neurons was maintained in vivo after engrafting into the mouse brain. Finally, demethylation of the CGG repeats in post-mitotic FXS neurons also reactivated FMR1. Our data establish that demethylation of the CGG expansion is sufficient for FMR1 reactivation, suggesting potential therapeutic strategies for FXS.