外周血淋巴细胞FMRP检测在脆性X综合征中的应用

目的 探讨外周血脆性X智力低下蛋白(fragile X mental retardation protein,FMRP)表达对脆性X综合征(fragile X syndrome,FXS)的诊断价值.方法 运用免疫细胞化学方法对38例不明原因的智力低下男性患儿的FMRP进行外周血淋巴细胞FMRP表达检测,并与38例年龄相近、智商或发育商均大于85的正常男性患儿比较,同时对FXS儿童FMRP表达水平与智力水平进行相关分析.结果 通过FMRP检测,智力低下组符合FXS诊断标准者5例,正常对照组外周血淋巴细胞FMRP表达均未达到诊断标准(P=0.022);FXS患儿FMRP表达率与发育商或智商间的相关性没有统计学意义(r=-0.610,P=0.275).结论 外周血淋巴细胞FMRP免疫细胞化学检测方法是一种具有快速、简便、价廉等优点的FXS实验诊断方法,可以用作FXS的诊断和筛查.     

脆性X智力低下蛋白与mRNAs的相互作用

脆性X智力低下蛋白(fragile mental retardation protein,FMRP)的表达缺失引起一种遗传性智力低下疾病——脆性X综合征。此蛋白是一种RNA结合蛋白,与mRNAs转运及多聚核糖体和突触的功能有关。因此,要了解脆性X综合征的发病机理,关键在于找到与FMRP蛋白结合的mRNAs,以及FMRP与这些靶mRNAs的结合对它们的代谢和翻译有何影响。     

Metabotropic Glutamate Receptor 5 Upregulation in Children with Autism is Associated with Underexpression of Both Fragile X Mental Retardation Protein and GABAA Receptor Beta 3 in Adults with Autism

Recent work has demonstrated the impact of dysfunction of the GABAergic signaling system in brain and the resultant behavioral pathologies in subjects with autism. In animal models, altered expression of Fragile X mental retardation protein (FMRP) has been linked to downregulation of GABA receptors. Interestingly, the autistic phenotype is also observed in individuals with Fragile X syndrome. This study was undertaken to test previous theories relating abnormalities in levels of FMRP to GABA_A receptor underexpression. We observed a significant reduction in levels of FMRP in the vermis of adults with autism. Additionally, we found that levels of metabotropic glutamate receptor 5 (mGluR5) protein were significantly increased in vermis of children with autism versus age and postmortem interval matched controls. There was also a significant decrease in level of GABA_A receptor beta 3 (GABRβ3) protein in vermis of adult subjects with autism. Finally, we found significant increases in glial fibrillary acidic protein in vermis of both children and adults with autism when compared with controls. Taken together, our results provide further evidence that altered FMRP expression and increased mGluR5 protein production potentially lead to altered expression of GABA_A receptors. Anat Rec,, 2011. © 2011 Wiley‐Liss, Inc.     

The fragile X mental retardation protein binds and regulates a novel class of mRNAs containing U rich target sequences

Fragile X syndrome is a common form of inherited mental retardation caused by the absence of the fragile X mental retardation protein (FMRP). It has been hypothesized that FMRP is involved in the processing and/or translation of mRNAs. Human and mouse target-mRNAs, containing purine quartets, have previously been identified. By using cDNA-SELEX (systematic evolution of ligands by exponential enrichment), we identified another class of human target-mRNAs which contain U rich sequences. This technique, in contrast to oligonucleotide-based SELEX, allows the identification of FMRP targets directly from mRNA pools. Many of the proteins encoded by the identified FMRP targets have been implicated in neuroplasticity. Steady state levels of target-mRNAs were unchanged in the brain of fragile X mice. However, levels of two target-encoded proteins, an L-type calcium channel subunit and MAP1B, were downregulated in specific brain regions suggesting a defect in the expression of target-encoded proteins in fragile X syndrome.     

Mutation intolerant genes and targets of FMRP are enriched for nonsynonymous alleles in schizophrenia

Risk of schizophrenia is conferred by alleles occurring across the full spectrum of frequencies from common SNPs of weak effect through to ultra rare alleles, some of which may be moderately to highly penetrant. Previous studies have suggested that some of the risk of schizophrenia is attributable to uncommon alleles represented on Illumina exome arrays. Here, we present the largest study of exomic variation in schizophrenia to date, using samples from the United Kingdom and Sweden (10,011 schizophrenia cases and 13,791 controls). Single variants, genes, and gene sets were analyzed for association with schizophrenia. No single variant or gene reached genome‐wide significance. Among candidate gene sets, we found significant enrichment for rare alleles (minor allele frequency [MAF] < 0.001) in genes intolerant of loss‐of‐function (LoF) variation and in genes whose messenger RNAs bind to fragile X mental retardation protein (FMRP). We further delineate the genetic architecture of schizophrenia by excluding a role for uncommon exomic variants (0.01 ≤ MAF ≥ 0.001) that confer a relatively large effect (odds ratio [OR] > 4). We also show risk alleles within this frequency range exist, but confer smaller effects and should be identified by larger studies.     

Identification of Fragile X Syndrome Specific Molecular Markers in Human Fibroblasts: A Useful Model to Test the Efficacy of Therapeutic Drugs

Fragile X syndrome (FXS) is the most frequent cause of inherited intellectual disability and autism. It is caused by the absence of the fragile X mental retardation 1 (FMR1) gene product, fragile X mental retardation protein (FMRP), an RNA‐binding protein involved in the regulation of translation of a subset of brain mRNAs. In Fmr1 knockout mice, the absence of FMRP results in elevated protein synthesis in the brain as well as increased signaling of many translational regulators. Whether protein synthesis is also dysregulated in FXS patients is not firmly established. Here, we demonstrate that fibroblasts from FXS patients have significantly elevated rates of basal protein synthesis along with increased levels of phosphorylated mechanistic target of rapamycin (p‐mTOR), phosphorylated extracellular signal regulated kinase 1/2, and phosphorylated p70 ribosomal S6 kinase 1 (p‐S6K1). The treatment with small molecules that inhibit S6K1 and a known FMRP target, phosphoinositide 3‐kinase (PI3K) catalytic subunit p110β, lowered the rates of protein synthesis in both control and patient fibroblasts. Our data thus demonstrate that fibroblasts from FXS patients may be a useful in vitro model to test the efficacy and toxicity of potential therapeutics prior to clinical trials, as well as for drug screening and designing personalized treatment approaches.     

Audiogenic seizure susceptibility is reduced in fragile X knockout mice after introduction of FMR1 transgenes

The Fmr1 knockout (KO) mouse is characterized by an increased audiogenic seizure (AGS) susceptibility and is considered a good animal model for epilepsy and seizures in the human fragile-X (FRAX) syndrome. Here, we tested the hypothesis that the reintroduction of the FMR1 gene is able to revert the AGS susceptibility characterizing Fmr1 KO mice. To this aim, two groups of Fmr1 KO transgenic mice, which have additional copies of the human FMR1 gene (YAC) or FMR1 cDNA (G6) were used. AGS susceptibility of these mice was examined and compared to that of Fmr1 KO, wild type, and wild-type animals in whom the FMR1gene was also introduced (over-expressed). Mice were tested at different ages because AGS susceptibility is age dependent. The intensity of response was scored and the results were analyzed by means of 2-way analysis of variance to evaluate the effects of age and genetic condition. We found that AGS susceptibility rescue is complete in the G6 mice and partial in YAC mice. Our data indicate that the introduction of the human FMR1 gene in Fmr1 KO mice is able to revert the Fmr1 KO epileptic phenotype.