Tandem repeats represent one of the most abundant class of variations in human genomes, which are polymorphic by nature and become highly unstable in a length-dependent manner. The expansion of ...repeat length across generations is a well-established process that results in human disorders mainly affecting the central nervous system. At least 50 disorders associated with expansion loci have been described to date, with half recognized only in the last ten years, as prior methodological difficulties limited their identification. These limitations still apply to the current widely used molecular diagnostic methods (exome or gene panels) and thus result in missed diagnosis detrimental to affected individuals and their families, especially for disorders that are very rare and/or clinically not recognizable. Most of these disorders have been identified through family-driven approaches and many others likely remain to be identified. The recent development of long-read technologies provides a unique opportunity to systematically investigate the contribution of tandem repeats and repeat expansions to the genetic architecture of human disorders. In this review, we summarize the current and most recent knowledge about the genetics of repeat expansion disorders and the diversity of their pathophysiological mechanisms and outline the perspectives of developing personalized treatments in the future.
Tandem repeats represent one of the most abundant class of variations in human genomes, which are polymorphic by nature and become highly unstable in a length-dependent manner. The expansion of repeat length across generations is a well-established process that results in human disorders mainly affecting the central nervous system. At least 50 disorders associated with expansion loci have been described to date, with half recognized only in the last ten years, as prior methodological difficulties limited their identification. These limitations still apply to the current widely used molecular diagnostic methods (exome or gene panels) and thus result in missed diagnosis detrimental to affected individuals and their families, especially for disorders that are very rare and/or clinically not recognizable. Most of these disorders have been identified through family-driven approaches and many others likely remain to be identified. The recent development of long-read technologies provides a unique opportunity to systematically investigate the contribution of tandem repeats and repeat expansions to the genetic architecture of human disorders. In this review, we summarize the current and most recent knowledge about the genetics of repeat expansion disorders and the diversity of their pathophysiological mechanisms and outline the perspectives of developing personalized treatments in the future.
Because of the unbalanced sex ratio (1.3–1.4 to 1) observed in intellectual disability (ID) and the identification of large ID-affected families showing X-linked segregation, much attention has been ...focused on the genetics of X-linked ID (XLID). Mutations causing monogenic XLID have now been reported in over 100 genes, most of which are commonly included in XLID diagnostic gene panels. Nonetheless, the boundary between true mutations and rare non-disease-causing variants often remains elusive. The sequencing of a large number of control X chromosomes, required for avoiding false-positive results, was not systematically possible in the past. Such information is now available thanks to large-scale sequencing projects such as the National Heart, Lung, and Blood (NHLBI) Exome Sequencing Project, which provides variation information on 10,563 X chromosomes from the general population. We used this NHLBI cohort to systematically reassess the implication of 106 genes proposed to be involved in monogenic forms of XLID. We particularly question the implication in XLID of ten of them (AGTR2, MAGT1, ZNF674, SRPX2, ATP6AP2, ARHGEF6, NXF5, ZCCHC12, ZNF41, and ZNF81), in which truncating variants or previously published mutations are observed at a relatively high frequency within this cohort. We also highlight 15 other genes (CCDC22, CLIC2, CNKSR2, FRMPD4, HCFC1, IGBP1, KIAA2022, KLF8, MAOA, NAA10, NLGN3, RPL10, SHROOM4, ZDHHC15, and ZNF261) for which replication studies are warranted. We propose that similar reassessment of reported mutations (and genes) with the use of data from large-scale human exome sequencing would be relevant for a wide range of other genetic diseases.
Targeting of messenger RNAs (mRNAs) in neuron processes relies on cis‐acting regulatory elements, the nature of which is poorly understood. Here, we report that approximately 30% of the best‐known ...dendritic mRNAs contain a guanine (G)–quadruplex consensus in their 3′‐untranslated region. Among these mRNAs, we show by using RNA structure probing that a G–quadruplex is present in the mRNAs of two key postsynaptic proteins: PSD‐95 and CaMKIIa. The G–quadruplex structure is necessary and sufficient for the potent and fast localization of mRNAs in cortical neurites and this occurs in a metabotropic glutamate receptor‐responsive manner. Thus, G–quadruplex seems to be a common neurite localization signal.
Guanine‐quadruplex structures in the 3'‐UTR of neuronal mRNAs are shown to function as a neurite mRNA localization signal in mouse cortical neurons in a metabotrobic glutamate receptor‐responsive manner.
Salivary gland disorders Mandel, Louis
The Medical clinics of North America,
11/2014, Letnik:
98, Številka:
6
Journal Article
Recenzirano
Patients with salivary gland disease present with certain objective and/or subjective signs. An accurate diagnosis for these patients requires a range of techniques that includes the organized ...integration of information derived from their history, clinical examination, imaging, serology, and histopathology. This article highlights the signs and symptoms of the salivary gland disorders seen in the Salivary Gland Center, and emphasizes the methodology used to achieve a definitive diagnosis and therapy.
DYRK1A and Wiedemann–Steiner syndromes (WSS) are two genetic conditions associated with neurodevelopmental disorders (NDDs). Although their clinical phenotype has been described, their behavioral ...phenotype has not systematically been studied using standardized assessment tools. To characterize the latter, we conducted a retrospective study, collecting data on developmental history, autism spectrum disorder (ASD), adaptive functioning, behavioral assessments, and sensory processing of individuals with these syndromes (n = 14;21). In addition, we analyzed information collected from families (n = 20;20) using the GenIDA database, an international patient‐driven data collection aiming to better characterize natural history of genetic forms of NDDs. In the retrospective study, individuals with DYRK1A syndrome showed lower adaptive behavior scores compared to those with WSS, whose scores showed greater heterogeneity. An ASD diagnosis was established for 57% (8/14) of individuals with DYRK1A syndrome and 24% (5/21) of those with WSS. Language and communication were severely impaired in individuals with DYRK1A syndrome, which was also evident from GenIDA data, whereas in WSS patients, exploration of behavioral phenotypes revealed the importance of anxiety symptomatology and ADHD signs, also flagged in GenIDA. This study, describing the behavioral and sensorial profiles of individuals with WSS and DYRK1A syndrome, highlighted some specificities important to be considered for patients' management.
Nucleoporins (Nups) build highly organized nuclear pore complexes (NPCs) at the nuclear envelope (NE). Several Nups assemble into a sieve‐like hydrogel within the central channel of the NPCs. In the ...cytoplasm, the soluble Nups exist, but how their assembly is restricted to the NE is currently unknown. Here, we show that fragile X‐related protein 1 (FXR1) can interact with several Nups and facilitate their localization to the NE during interphase through a microtubule‐dependent mechanism. Downregulation of FXR1 or closely related orthologs FXR2 and fragile X mental retardation protein (FMRP) leads to the accumulation of cytoplasmic Nup condensates. Likewise, models of fragile X syndrome (FXS), characterized by a loss of FMRP, accumulate Nup granules. The Nup granule‐containing cells show defects in protein export, nuclear morphology and cell cycle progression. Our results reveal an unexpected role for the FXR protein family in the spatial regulation of nucleoporin condensation.
Synopsis
Fragile X‐related proteins and dynein inhibit ectopic phase separation of nucleoporins in the cytoplasm and facilitate their localization to the nuclear envelope during G1 phase of the cell cycle.
Fragile X‐related (FXR) proteins and dynein regulate localization of cytoplasmic nucleoporins.
FXR‐Dynein pathway downregulation induces aberrant cytoplasmic condensation of nucleoporins.
Cellular models of Fragile X syndrome accumulate aberrant cytoplasmic nucleoporin condensates.
FXR‐Dynein pathway regulates nuclear morphology and cell cycle progression.
Fragile X‐related proteins and dynein inhibit ectopic phase separation of nucleoporins in the cytoplasm and facilitate their localization to the nuclear envelope during G1 phase of the cell cycle.
The X‐linked NLGN3 gene, encoding a postsynaptic cell adhesion molecule, was involved in a nonsyndromic monogenic form of autism spectrum disorder (ASD) by the description of one unique missense ...variant, p.Arg451Cys (Jamain et al. 2003). We investigated here the pathogenicity of additional missense variants identified in two multiplex families with intellectual disability (ID) and ASD: c.1789C>T, p.Arg597Trp, previously reported by our group (Redin et al. 2014) and present in three affected cousins and c.1540C>T, p.Pro514Ser, identified in two affected brothers. Overexpression experiments in HEK293 and HeLa cell lines revealed that both variants affect the level of the mature NLGN3 protein, its localization at the plasma membrane and its presence as a cleaved form in the extracellular environment, even more drastically than what was reported for the initial p.Arg451Cys mutation. The variants also induced an unfolded protein response, probably due to the retention of immature NLGN3 proteins in the endoplasmic reticulum. In comparison, the c.1894A>G, p.Ala632Thr and c.1022T>C, p.Val341Ala variants, present in males from the general population, have no effect. Our report of two missense variants affecting the normal localization of NLGN3 in a total of five affected individuals reinforces the involvement of the NLGN3 gene in a neurodevelopmental disorder characterized by ID and ASD.
Our study reports the characterization of two novel missense variants in NLGN3, causing a nonsyndromic form of ID associated with autistic manifestations. The variants studied lead to an absence/decrease of membrane localization of NLGN3, its retention in the endoplasmic reticulum (ER) and induction of a cellular response related to ER stress.
Prenatal exposure to androgens during brain development in male individuals may participate to increase their susceptibility to develop neurodevelopmental disorders such as autism spectrum disorder ...(ASD) and intellectual disability. However, little is known about the action of androgens in human neural cells.
We used human neural stem cells differentiated from embryonic stem cells to investigate targets of androgens.
RNA sequencing revealed that treatment with dihydrotestosterone (DHT) leads to subtle but significant changes in the expression of about 200 genes, encoding proteins of extracellular matrix or involved in signal transduction of growth factors (e.g., insulin/insulin growth factor 1). We showed that the most differentially expressed genes (DEGs), RGCC, RNF144B, NRCAM, TRIM22, FAM107A, IGFBP5, and LAMA2, are reproducibly regulated by different androgens in different genetic backgrounds. We showed, by overexpressing the androgen receptor in neuroblastoma cells SH-SY5Y or knocking it down in human neural stem cells, that this regulation involves the androgen receptor. A chromatin immunoprecipitation combined with direct sequencing analysis identified androgen receptor–bound sequences in nearly half of the DHT-DEGs and in numerous other genes. DHT-DEGs appear enriched in genes involved in ASD (ASXL3, NLGN4X, etc.), associated with ASD (NRCAM), or differentially expressed in patients with ASD (FAM107A, IGFBP5). Androgens increase human neural stem cell proliferation and survival in nutrient-deprived culture conditions, with no detectable effect on regulation of neurite outgrowth.
We characterized androgen action in neural progenitor cells, identifying DHT-DEGs that appear to be enriched in genes related to ASD. We also showed that androgens increase proliferation of neuronal precursors and protect them from death during their differentiation in nutrient-deprived conditions.
Fragile X syndrome (FXS) is the most frequent form of familial intellectual disability. FXS results from the lack of the RNA‐binding protein FMRP and is associated with the deregulation of signaling ...pathways downstream of mGluRI receptors and upstream of mRNA translation. We previously found that diacylglycerol kinase kappa (DGKk), a main mRNA target of FMRP in cortical neurons and a master regulator of lipid signaling, is downregulated in the absence of FMRP in the brain of Fmr1‐KO mouse model. Here we show that adeno‐associated viral vector delivery of a modified and FMRP‐independent form of DGKk corrects abnormal cerebral diacylglycerol/phosphatidic acid homeostasis and FXS‐relevant behavioral phenotypes in the Fmr1‐KO mouse. Our data suggest that DGKk is an important factor in FXS pathogenesis and provide preclinical proof of concept that its replacement could be a viable therapeutic strategy in FXS.
Synopsis
Brain neuron‐restricted expression of an FMRP‐independent DGKk enzyme via intra‐cerebral adeno‐associated virus (AAV) gene therapy corrects phosphatidic acid deficiency and rescues disease relevant behavioral phenotypic alterations in a mouse model of Fragile X syndrome (FXS).
The expression of diacylglycerol kinase kappa (DGKk), a favored mRNA target of FMRP, is reduced in the FXS brain in both humans and mice.
∆N‐DGKk is a truncated active enzyme whose synthesis bypasses the need for FMRP.
AAV‐Rh10‐∆N‐DGKk enables the synthesis of active DGKk enzyme in neurons lacking FMRP.
∆N‐DGKk neuronal expression has no adverse effect in wild type control mice and is associated with normal behavioral functions of the rescued Fmr1‐null mice.
Brain neuron‐restricted expression of an FMRP‐independent DGKk enzyme via intra‐cerebral adeno‐associated virus (AAV) gene therapy corrects phosphatidic acid deficiency and rescues disease relevant behavioral phenotypic alterations in a mouse model of Fragile X syndrome (FXS).
Mutations in the phosphoinositide phosphatase myotubularin (MTM1) results in X‐linked myotubular/centronuclear myopathy (XLMTM), characterized by a severe decrease in muscle mass and strength in ...patients and murine models. However, the molecular mechanism involved in the muscle hypotrophy is unclear. Here we show that the IGF1R/Akt pathway is affected in Mtm1‐deficient murine muscles, characterized by an increase in IGF1 receptor and Akt levels in both the presymptomatic and symptomatic phases. Moreover, up‐regulation of atrogenes was observed in the presymptomatic phase of the myopathy, supporting overactivation of the ubiquitin‐proteasome pathway. In parallel, the autophagy machinery was affected as indicated by the increase in the number of autophagosomes and of autophagy markers, such as LC3 and P62. However, phosphorylation of FOXO3a and mTOR were abnormal at late but not at early stages of the disease, suggesting that myotubularin acts both upstream in the IGF1R/Akt pathway and downstream on the balance between the autophagy and ubiquitin‐proteasome pathways in vivo. Adeno‐associated virus‐mediated delivery of Mtm1 into Mtm1‐null muscles rescued muscle mass and normalized the expression levels of IGF1 receptor, the ubiquitin‐proteasome pathway, and autophagy markers. These data support the hypothesis that the unbalanced regulation of the ubiquitin proteasome pathway and the autophagy machinery is a primary cause of the XLMTM pathogenesis.—Al‐Qusairi, L., Prokic, I., Amoasii, L., Kretz, C., Messaddeq, N., Mandel, J.‐L., Laporte, J. Lack of myotubularin (MTM1) leads to muscle hypotrophy through unbalanced regulation of the autophagy and ubiquitin‐proteasome pathways. FASEB J. 27, 3384–3394 (2013). www.fasebj.org
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