Retards mentaux liés à l’X

Les retards mentaux liés au chromosome X (RMLX), qui touchent 1,8 garçons pour 1 000 naissances masculines, sont classiquement divisés en formes syndromiques et formes non spécifiques, selon la présence ou non de signes particuliers associés au retard mental. L’extrême hétérogénéité phénotypique et allélique, parfois visible au sein d’une même famille, complique toutefois cette classification. L’évaluation rétrospective appronfondie des familles atteintes, une fois la mutation identifiée dans un gène, devrait aider à clarifier la situation et faciliter la prise en charge du diagnostic moléculaire de ces retards mentaux. L’analyse des protéines produites par les 60 gènes de RMLX actuellement identifiés montre une grande diversité des fonctions biologiques affectées dans le retard mental. Dans cette revue, nous présenterons les données récentes concernant trois gènes, FMR1, ARX et le gène de l’oligophrénine 1, qui non seulement illustrent la complexité des RMLX, mais soulignent aussi l’importance des voies de signalisation impliquées dans la régulation de l’expression génique, ainsi que celles relayées pas les GTPases Rho dans la maturation et la plasticité neuronale.X-linked mental retardation (XLMR) affects 1.8 ‰ male births and is usually categorized as “syndromic” (MRXS) or “non-specific” (MRX) forms according to the presence or absence of specific signs in addition to the MR. Up to 60 genes have been implicated in XLMR and certain mutations can alternatively lead to MRXS or MRX. Indeed the extreme phenotypic and allelic heterogeneity of XLMR makes the classification of most genes difficult. Therefore, following identification of new genes, accurate retrospective clinical evaluation of patients and their families is necessary to aid the molecular diagnosis and the classification of this heterogeneous group of disorders. Analyses of the protein products corresponding to XLMR genes show a great diversity of cellular pathways involved in MR. Common mechanisms are beginning to emerge : a first group of proteins belongs to the Rho and Rab GTPase signaling pathways involved in neuronal differentiation and synaptic plasticity and a second group is related to the regulation of gene expression. In this review, we illustrate the complexity of XLMR conditions and present recent data about the FMR1, ARX and Oligophrenin 1 genes

Physiopathologie des malformations du développement cortical associées à des mutations du gène tubuline b3

D une organisation très complexe, le cortex résulte de différents processus coordonnés qui comprennent la neurogenèse, la migration et la différenciation neuronales. L altération d un ou plusieurs de ces processus peut entrainer chez l homme l apparition de malformations du développement cortical (MDC).L identification de mutations chez des patients présentant des MDC dans les gènes DCX et LIS1 codant des protéines s associant directement ou indirectement aux microtubules a montré le rôle primordial du cytosquelette dans le développement cortical. Ce constat fut renforcé par la découverte de mutations dans des gènes codant des sous-unités tubulines elles-mêmes (TUBA1A, TUBB2B et TUBB5), unités structurelles et fonctionnelles des microtubules.Notre étude apporte des contributions à cette observation importante. En effet, nous avons tout d abord identifié l'existence de six mutations faux-sens dans le gène TUBB3, chez douze patients, incluant un cas fœtal. Les mutations ont été trouvées principalement à l'état hétérozygote et peuvent être de novo ou transmises selon un mode autosomique dominant. Tous les patients ont en commun des anomalies complexes du développement du cortex, évocatrices de polymicrogyries frontales ou de désorganisations et simplifications gyrales en combinaison avec des anomalies du corps calleux et de la capsule interne des ganglions de la base ainsi qu'une hypoplasie du pont et du cervelet. La deuxième partie de ce travail s intéresse à l effet de la perte d expression de la tubuline b3 et des mutations responsables de MDC sur les processus de la migration radiaire des neurones pyramidaux par une approche d électroporation in utero chez la souris. L inactivation de Tubb3 entraine un défaut de migration drastique : la majorité des cellules électroporées sont présentes dans la zone sous ventriculaire et la zone intermédiaire. Des explorations montrent une diminution du nombre de cellules multipolaires présentant des processus multiples et bien élongés, et une augmentation du nombre de cellules rondes ne présentant pas ou peu de processus. Ces résultats laissent penser que la diminution de Tubb3 entraine des défauts du contrôle des étapes de multipolarisation et rebipolarisation des neurones pyramidaux lors de la migration radiale. Nous avons également mis en évidence une augmentation de la population de progéniteurs intermédiaires électroporés avec l ARNsh anti-Tubb3. Cette augmentation est accompagnée d une forte diminution de leur division cellulaire. Ce résultat soulève de nombreuses questions sur le rôle potentiel de Tubb3 dans cette population. Enfin, nous avons pu constater que l arrêt de migration observé peut être sauvé par une surexpression du transcrit de TUBB3 alors que les tubulines TUBB1, TUBB2B et TUBB4A sont dans l incapacité de restaurer pleinement la migration radiaire des neurones sous exprimant Tubb3. Ces observations tendent à étayer l hypothèse selon laquelle les sous unités tubulines possèdent des spécificités fonctionnelles.Dans l ensemble, nos travaux montrent donc que des mutations de TUBB3 sont liées à des formes de MDC et que Tubb3 joue un rôle important dans la migration des neurones pyramidaux chez la souris, notamment par le contrôle des changements morphologiques qui interviennent dans la phase multipolaire. Enfin, nous apportons une nouvelle proposition d interdépendance entre l arrêt de migration neuronale et la division des progéniteurs neuronaux dans le développement cortical.Over the last years, the critical role of the cytoskeletal network in the proper cortical development has been established. The importance of microtubules was further emphasized with the association of mutations in gene encoding for alpha-tubulin (TUBA1A, TUBA8), beta-tubulin (TUBB2B) in malformations of cortical development (MCD) including lissencephalies and polymicrogyria (Keays 2007, Poirier 2007, Jaglin 2009, Abdollahi 2009) and TUBB5 in microcephaly with cortical gyration abnormalities. We report the implication of TUBB3 missense mutations in polymicrogyria and cortical simplifications in 6 different families including a foetal case harboring a severe micerolissencephaly.We investigated the properties of MT network in patients' fibroblasts and revealed that MCD-related mutations can alter the resistance of microtubules to depolymerisation. These results led us to hypothesise that either microtubule dynamics or their interactions with various MT interacting proteins could be differently affected by TUBB3 variations, thus resulting in distinct alteration of downstream processes and therefore explaining the phenotypic diversity of the TUBB3-related spectrum. In a second time, we investigate further the association between TUBB3 mutations and MCDs by analyzing the consequences of Tubb3 knockdown on cortical development in mice. Using the in utero electroporation approach, we demonstrate that Tubb3 knockdown leads to delayed bipolar morphology and radial migration with evidence suggesting that the neuronal arrest is a transient phenomenon overcome after birth. Silenced blocked cells display a round shape and decreased number of processes and a delay in the acquisition of the bipolar morphology. Also, more Tbr2 positive cells are observed, although less cells express the proliferation marker Ki67, suggesting that Tubb3 inactivation might have an indirect effect on intermediate progenitor proliferation. Furthermore, we show by rescue experiments the non interchangeability of other beta-tubulins which are unable to rescue the phenotype. Our study highlights the critical and specific role of Tubb3 on the stereotyped morphological changes and polarization processes that are required for initiating radial migration to the cortical plate.PARIS5-Bibliotheque electronique (751069902) / SudocSudocFranceF

De novo TUBB2B mutation causes fetal akinesia deformation sequence with microlissencephaly: an unusual presentation of tubulinopathy

International audienceTubulinopathies are increasingly emerging major causes underlying complex cerebral malformations, particularly in case of microlissencephaly often associated with hypoplastic or absent corticospinal tracts. Fetal akinesia deformation sequence (FADS) refers to a clinically and genetically heterogeneous group of disorders with congenital malformations related to impaired fetal movement. We report on an early foetal case with FADS and microlissencephaly due to TUBB2B mutation. Neuropathological examination disclosed virtually absent cortical lamination, foci of neuronal overmigration into the leptomeningeal spaces, corpus callosum agenesis, cerebellar and brainstem hypoplasia and extremely severe hypoplasia of the spinal cord with no anterior and posterior horns and almost no motoneurons. At the cellular level, the p.Cys239Phe TUBB2B mutant leads to tubulin heterodimerization impairment, decreased ability to incorporate into the cytoskeleton, microtubule dynamics alteration, with an accelerated rate of depolymerization. To our knowledge, this is the first case of microlissencephaly to be reported presenting with a so severe and early form of FADS, highlighting the importance of tubulin mutation screening in the context of FADS with microlissencephaly

A YAC contig in Xp21 containing the adrenal hypoplasia congenita and glycerol kinase deficiency genes

The gene loci for adrenal hypoplasia congenita (AHC) and glycerol kinase deficiency (GK) map in Xp21 distal to Duchenne muscular dystrophy (DMD), and proximal to DXS28 (C7), by analysis of patient deletions. We have constructed a yeast artificial chromosome (YAC) contig encompassing a 1.2 Mb region extending distally from DMD, and containing DXS708 (JC-1), the distal junction clone of a patient with GK and DMD. A pulsed-field gel electrophoresis map of the YAC contig identified 3 potential CpG islands. Whole YAC hybridization identified cosmids both for construction of cosmid contigs, and isolation of single copy probes. Thirteen new single copy probes and DXS28 and DXS708 were hybridized on a panel of patients; the deletion mapping indicates that the YAC contig contains both GK and at least part of AHC, and together with the physical map defines a GK critical region of 50-250 kb. In one AHC patient with a cytogenetically detectable deletion we used the new probes to characterize a complex double deletion. Non-overlapping deletions observed in other unrelated AHC patients indicate that the AHC gene is large, extending over at least 200-500 kb. This mapping provides the basis for the identification of the AHC and GK gene

A distinctive gene expression fingerprint in mentally retarded male patients reflects disease-causing defects in the histone demethylase KDM5C

Background: Mental retardation is a genetically heterogeneous disorder, as more than 90 genes for this disorder has been found on the X chromosome alone. In addition the majority of patients are non-syndromic in that they do not present with clinically recognisable features. This makes it difficult to determine the molecular cause of this disorder on the basis of the phenotype alone. Mutations in KDM5C (previously named SMCX or JARID1C), a gene that encodes a transcriptional regulator with histone demethylase activity specific for dimethylated and trimethylated H3K4, are a comparatively frequent cause of non-syndromic X-linked mental retardation (NS-XLMR). Specific transcriptional targets of KDM5C, however, are still unknown and the effects of KDM5C deficiency on gene expression have not yet been investigated. Results: By whole-mount in situ hybridisation we showed that the mouse homologue of KDM5C is expressed in multiple tissues during mouse development. We present the results of gene expression profiling performed on lymphoblastoid cell lines as well as blood from patients with mutations in KDM5C. Using whole genome expression arrays and quantitative reverse transcriptase polymerase chain reaction (QRT-PCR) experiments, we identified several genes, including CMKOR1, KDM5B and KIAA0469 that were consistently deregulated in both tissues. Conclusions: Our findings shed light on the pathological mechanisms underlying mental retardation and have implications for future diagnostics of this heterogeneous disorder

Mutation screening of ASMT, the last enzyme of the melatonin pathway, in a large sample of patients with intellectual disability.

International audienceBACKGROUND: Intellectual disability (ID) is frequently associated with sleep disorders. Treatment with melatonin demonstrated efficacy, suggesting that, at least in a subgroup of patients, the endogenous melatonin level may not be sufficient to adequately set the sleep-wake cycles. Mutations in ASMT gene, coding the last enzyme of the melatonin pathway have been reported as a risk factor for autism spectrum disorders (ASD), which are often comorbid with ID. Thus the aim of the study was to ascertain the genetic variability of ASMT in a large cohort of patients with ID and controls. METHODS: Here, we sequenced all exons of ASMT in a sample of 361 patients with ID and 440 controls. We then measured the ASMT activity in B lymphoblastoid cell lines (BLCL) of patients with ID carrying an ASMT variant and compared it to controls. RESULTS: We could identify eleven variations modifying the protein sequence of ASMT (ID only: N13H, N17K, V171M, E288D; controls only: E61Q, D210G, K219R, P243L, C273S, R291Q; ID and controls: L298F) and two deleterious splice site mutations (IVS5+2T>C and IVS7+1G>T) only observed in patients with ID. We then ascertained ASMT activity in B lymphoblastoid cell lines from patients carrying the mutations and showed significantly lower enzyme activity in patients carrying mutations compared to controls (p = 0.004). CONCLUSIONS: We could identify patients with deleterious ASMT mutations as well as decreased ASMT activity. However, this study does not support ASMT as a causative gene for ID since we observed no significant enrichment in the frequency of ASMT variants in ID compared to controls. Nevertheless, given the impact of sleep difficulties in patients with ID, melatonin supplementation might be of great benefit for a subgroup of patients with low melatonin synthesis

Mutation of the Diamond-Blackfan Anemia Gene Rps7 in Mouse Results in Morphological and Neuroanatomical Phenotypes

The ribosome is an evolutionarily conserved organelle essential for cellular function. Ribosome construction requires assembly of approximately 80 different ribosomal proteins (RPs) and four different species of rRNA. As RPs co-assemble into one multi-subunit complex, mutation of the genes that encode RPs might be expected to give rise to phenocopies, in which the same phenotype is associated with loss-of-function of each individual gene. However, a more complex picture is emerging in which, in addition to a group of shared phenotypes, diverse RP gene-specific phenotypes are observed. Here we report the first two mouse mutations (Rps7(Mtu) and Rps7(Zma)) of ribosomal protein S7 (Rps7), a gene that has been implicated in Diamond-Blackfan anemia. Rps7 disruption results in decreased body size, abnormal skeletal morphology, mid-ventral white spotting, and eye malformations. These phenotypes are reported in other murine RP mutants and, as demonstrated for some other RP mutations, are ameliorated by Trp53 deficiency. Interestingly, Rps7 mutants have additional overt malformations of the developing central nervous system and deficits in working memory, phenotypes that are not reported in murine or human RP gene mutants. Conversely, Rps7 mouse mutants show no anemia or hyperpigmentation, phenotypes associated with mutation of human RPS7 and other murine RPs, respectively. We provide two novel RP mouse models and expand the repertoire of potential phenotypes that should be examined in RP mutants to further explore the concept of RP gene-specific phenotypes.This research was supported in part by the Intramural Research Program of NHGRI, NIH, and the Wellcome Trust and by NHMRC Australia grant 366746. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Mutations in TUBG1, DYNC1H1, KIF5C and KIF2A cause malformations of cortical development and microcephaly.

International audienceThe genetic causes of malformations of cortical development (MCD) remain largely unknown. Here we report the discovery of multiple pathogenic missense mutations in TUBG1, DYNC1H1 and KIF2A, as well as a single germline mosaic mutation in KIF5C, in subjects with MCD. We found a frequent recurrence of mutations in DYNC1H1, implying that this gene is a major locus for unexplained MCD. We further show that the mutations in KIF5C, KIF2A and DYNC1H1 affect ATP hydrolysis, productive protein folding and microtubule binding, respectively. In addition, we show that suppression of mouse Tubg1 expression in vivo interferes with proper neuronal migration, whereas expression of altered γ-tubulin proteins in Saccharomyces cerevisiae disrupts normal microtubule behavior. Our data reinforce the importance of centrosomal and microtubule-related proteins in cortical development and strongly suggest that microtubule-dependent mitotic and postmitotic processes are major contributors to the pathogenesis of MCD

A YAC contig in Xp21 containing the adrenal hypoplasia congenita and glycerol kinase deficiency genes

The gene loci for adrenal hypoplasia congenita (AHC) and glycerol kinase deficiency (GK) map in Xp21 distal to Duchenne muscular dystrophy (DMD), and proximal to DXS28 (C7), by analysis of patient deletions. We have constructed a yeast artificial chromosome (YAC) contig encompassing a 1.2 Mb region extending distally from DMD, and containing DXS708 (JC-1), the distal junction clone of a patient with GK and DMD. A pulsed-field gel electrophoresis map of the YAC contig identified 3 potential CpG islands. Whole YAC hybridization identified cosmids both for construction of cosmid contigs, and isolation of single copy probes. Thirteen new single copy probes and DXS28 and DXS708 were hybridized on a panel of patients; the deletion mapping indicates that the YAC contig contains both GK and at least part of AHC, and together with the physical map defines a GK critical region of 50-250 kb. In one AHC patient with a cytogenetically detectable deletion we used the new probes to characterize a complex double deletion. Non-overlapping deletions observed in other unrelated AHC patients indicate that the AHC gene is large, extending over at least 200-500 kb. This mapping provides the basis for the identification of the AHC and GK gene

Erratum to: Mutation screening in 86 known X-linked mental retardation genes by droplet-based multiplex PCR and massive parallel sequencing

Item does not contain fulltext[This corrects the article DOI: 10.1007/s11568-010-9137-y.].1 december 200