A missense variant in the nuclear export signal of the FMR1 gene causes intellectual disability

Comprehensive systematic review and meta-analysis of the association between common genetic variants and autism spectrum disorder

BACKGROUND

Autism spectrum disorder (ASD) is neurodevelopmental disorder characterized by stereotyped behavior and deficits in communication and social interactions. To date, numerous studies have investigated the associations between genetic variants and ASD risk. However, the results of these published studies lack a clear consensus. In the present study, we performed a systematic review on the association between genetic variants and ASD risk. Meanwhile, we conducted a meta-analysis on available data to identify the association between the single nucleotide polymorphisms (SNPs) of candidate genes and ASD risk.

METHODS

We systematically searched public databases including English and Chinese from their inception to August 1, 2022. Two independent reviewers extracted data and assessed study quality. Odds ratio and 95 % confidence interval were used as effect indexes to evaluate the association between the SNPs of candidate genes and the risk of ASD. Heterogeneity was explored through subgroup, sensitivity, and meta-regression analyses. Publication bias was assessed by using Egger's and Begg's tests for funnel plot asymmetry. In addition, TSA analysis were performed to confirm the study findings.

RESULTS

We summarized 84 SNPs of 32 candidate genes from 81 articles included in the study. Subsequently, we analyzed 16 SNPs of eight genes by calculating pooled ORs, and identified eight significant SNPs of contactin associated protein 2 (CNTNAP2), methylentetrahydrofolate reductase (MTHFR), oxytocin receptor (OXTR), and vitamin D receptor (VDR). Results showed that seven SNPs, including the CNTNAP2 rs2710102 (homozygote, heterozygote, dominant and allelic models) and rs7794745 (heterozygote and dominant models), MTHFR C677T (homozygote, heterozygote, dominant, recessive and allelic models) and A1298C (dominant and allelic models), OXTR rs2254298 (homozygote and recessive models), VDR rs731236 (homozygote, dominant, recessive and allelic models) and rs2228570 (homozygote and recessive models), were showed to be correlated with an increased ASD risk. By contrast, the VDR rs7975232 was correlated with a decreased the risk of ASD under the homozygote and allelic models.

CONCLUSION

Our study summarized research evidence on the genetic variants of ASD and provides a broad and detailed overview of ASD risk genes. The C677T and A1298C polymorphisms of MTHFR, rs2710102 and rs7794745 polymorphisms of CNTNAP2, rs2254298 polymorphism of OXTR, and rs731236 and rs2228570 polymorphisms of VDR were genetic risk factors. The rs7975232 polymorphism of VDR was a genetic protective factor for ASD. Our study provides novel clues to clinicians and healthcare decision-makers to predict ASD susceptibility.

Mouse models of fragile X-related disorders

The fragile X-related disorders are an important group of hereditary disorders that are caused by expanded CGG repeats in the 5' untranslated region of the FMR1 gene or by mutations in the coding sequence of this gene. Two categories of pathological CGG repeats are associated with these disorders, full mutation alleles and shorter premutation alleles. Individuals with full mutation alleles develop fragile X syndrome, which causes autism and intellectual disability, whereas those with premutation alleles, which have shorter CGG expansions, can develop fragile X-associated tremor/ataxia syndrome, a progressive neurodegenerative disease. Thus, fragile X-related disorders can manifest as neurodegenerative or neurodevelopmental disorders, depending on the size of the repeat expansion. Here, we review mouse models of fragile X-related disorders and discuss how they have informed our understanding of neurodegenerative and neurodevelopmental disorders. We also assess the translational value of these models for developing rational targeted therapies for intellectual disability and autism disorders.

Combining affinity purification and mass spectrometry to define the network of the nuclear proteins interacting with the N-terminal region of FMRP

Fragile X-Syndrome (FXS) represents the most common inherited form of intellectual disability and the leading monogenic cause of Autism Spectrum Disorders. In most cases, this disease results from the absence of expression of the protein FMRP encoded by the FMR1 gene (Fragile X messenger ribonucleoprotein 1). FMRP is mainly defined as a cytoplasmic RNA-binding protein regulating the local translation of thousands of target mRNAs. Interestingly, FMRP is also able to shuttle between the nucleus and the cytoplasm. However, to date, its roles in the nucleus of mammalian neurons are just emerging. To broaden our insight into the contribution of nuclear FMRP in mammalian neuronal physiology, we identified here a nuclear interactome of the protein by combining subcellular fractionation of rat forebrains with pull‐ down affinity purification and mass spectrometry analysis. By this approach, we listed 55 candidate nuclear partners. This interactome includes known nuclear FMRP-binding proteins as Adar or Rbm14 as well as several novel candidates, notably Ddx41, Poldip3, or Hnrnpa3 that we further validated by target‐specific approaches. Through our approach, we identified factors involved in different steps of mRNA biogenesis, as transcription, splicing, editing or nuclear export, revealing a potential central regulatory function of FMRP in the biogenesis of its target mRNAs. Therefore, our work considerably enlarges the nuclear proteins interaction network of FMRP in mammalian neurons and lays the basis for exciting future mechanistic studies deepening the roles of nuclear FMRP in neuronal physiology and the etiology of the FXS.

Genetic determinants of autism spectrum disorders - a review

Introduction: It is estimated that various types of abnormalities from the autistic spectrum disorder occur in up to 2% of the population. These include difficulties in maintaining relationships, communication, and repetitive behaviours. Literature describes them quite well, in contrast to the causes of these disorders, which include both environmental factors and a very long list of genetic aberrations.

Materials and methods: The papers available on the PubMed platform and other sources were reviewed to describe the most important genetic factors responsible for the development of autism spectrum disorders.

Results: There are many genes and their mutations associated with the prevalence of autism spectrum disorders in patients. One of the main factors is the SHANK gene family, with the type and degree of abnormality in patients depending on the damage to particular genes: SHANK1-SHANK3. Research also shows the potential of targeted symptom-relieving therapies in patients with SHANK3 mutations. A correlation with the occurrence of autism has also been demonstrated for genes responsible for calcium signaling - especially the group of IP3R calcium channels. Their calcium transmission is abnormal in the majority of patients with autism spectrum disorders. A number of mutations in the 7q region were discovered - including the AUTS2, GNAI1, RELN, KMT2E, BRAF genes - the occurrence of which is associated with the presence of symptoms of autism. Autism spectrum disorders occur in about 10% of patients suffering from monogenic syndromes such as fragile X chromosome syndrome, Timothy syndrome, tuberous sclerosis, Rett syndrome or hamartomatic tumor syndrome.

Conclusions: Research shows that many mutations can contribute to the development of autism spectrum disorders. Further studies are necessary to discover their therapeutic and diagnostic potential for autism.

Beyond Trinucleotide Repeat Expansion in Fragile X Syndrome: Rare Coding and Noncoding Variants in FMR1 and Associated Phenotypes

FMR1 (FMRP translational regulator 1) variants other than repeat expansion are known to cause disease phenotypes but can be overlooked if they are not accounted for in genetic testing strategies. We collected and reanalyzed the evidence for pathogenicity of FMR1 coding, noncoding, and copy number variants published to date. There is a spectrum of disease-causing FMR1 variation, with clinical and functional evidence supporting pathogenicity of five splicing, five missense, one in-frame deletion, one nonsense, and four frameshift variants. In addition, FMR1 deletions occur in both mosaic full mutation patients and as constitutional pathogenic alleles. De novo deletions arise not only from full mutation alleles but also alleles with normal-sized CGG repeats in several patients, suggesting that the CGG repeat region may be prone to genomic instability even in the absence of repeat expansion. We conclude that clinical tests for potentially FMR1-related indications such as intellectual disability should include methods capable of detecting small coding, noncoding, and copy number variants.