Fragile X Syndrome (FXS) occurs as a result of a silenced fragile X mental retardation 1 gene (<i>FMR1</i>) and subsequent loss of fragile X mental retardation protein (FMRP) expression.
This study suggests that intragenic FMR1 variants, although much less frequent than CGG expansions, are a significant mutational mechanism leading to FXS and demonstrates the interest of HTS approaches to detect them in ID patients with a negative standard work-up.
A point mutation (I304N) in the KH2 domain, identified from a Fragile X syndrome patient, disrupts the FMRP-nucleoprotein association and abolishes the ability of FMRP to participate in viral RNP assembly.
These findings suggest that nuclear FMRP regulates genomic stability at the chromatin interface and may impact gametogenesis and some developmental aspects of fragile X syndrome.
Herein, we discuss the molecular mechanisms leading to FXS and the Prader-Willi phenotype with an emphasis on mouse FMR1 knockout studies that have shown the reversal of weight increase through mGluR antagonists.
We conclude that further studies including western blot and DNA sequence analysis of the FMR1 gene should be performed in patients with typical symptoms of fragile X syndrome in whom no CGG repeat expansion is detected.
Mice with deletion of the fragile X mental retardation 1 (Fmr1) gene are used to model autism because loss of Fmr1 gene function causes Fragile X Syndrome (FXS) and many people with FXS exhibit autistic-like behaviors.
These mice phenocopy the symptoms of Fragile X Syndrome in the existing Fmr1-null mouse, as assessed by testicular size, behavioral phenotyping, and electrophysiological assays of synaptic plasticity.
Subjects with FXS and fragile X mental retardation gene knock out (Fmr1 KO) mice, an animal model for FXS, have been shown to exhibit defects in dendritic spine maturation that may underlie cognitive and behavioural abnormalities in FXS.
We propose a contribution of Tdrd3 to FMRP-mediated translational repression and suggest that the loss of the FMRP-Tdrd3 interaction caused by the I304N mutation might contribute to the pathogenesis of Fragile X syndrome.
Here, we present an X-ray crystal structure of the tandem KH domains of human FMRP, which reveals the relative orientation of the KH1 and KH2 domains and the location of residue Ile304, whose mutation to Asn is associated with a particularly severe incidence of Fragile X syndrome.
We conclude that mental retardation associated with the I304N mutation, and likely the Fragile-X syndrome more generally, may relate to a crucial role for RNAs harboring the kissing complex motif as targets for FMRP translational regulation.
Fragile X syndrome is caused by the absence of the mRNA-binding protein Fragile X mental retardation protein (FMRP), which may play a role in activity-regulated localization and translation of mRNA in dendrites and at synapses.
We further suggest that the failure of FMRP to oligomerize, caused by the I304N mutation, may contribute to the pathophysiological events leading to fragile X syndrome.