The regulation of neural precursor cells (NPCs), which encompass neural progenitor and neural stem cells (NSCs), is fundamental for proper brain development and function. These cells are regulated by orchestrated signalling within their local environment. Aberrant aspects of cell proliferation, differentiation, survival, or integration have been linked to various neurological diseases including Fragile X syndrome (FXS)—a disorder characterized by intellectual and social changes due to the silencing of the gene encoding FMRP. The biology of hippocampal NPCs in FXS during early postnatal development has not been studied, despite high FMRP expression levels in the hippocampus at the end of the first postnatal week. In this thesis, the Fmr1-knockout (KO) mouse model was used to study hippocampal cell biology during early postnatal development. A tissue culture assay, used to study the effect of astrocyte-secreted factors on the proliferation of NSCs, indicated that astrocyte secreted factors from Fmr1-KO brains enhanced the proliferation of wild type, but not Fmr1-KO NSCs (Chapter 3). Next, the proliferation and cell cycle profiles of NPCs in vitro and in vivo studied with immunocytochemistry, Western blotting, and flow cytometry revealed decreased proliferation of NPCs in the Fmr1-KO hippocampus (Chapter 4). Finally, cells isolated from the P7 dentate gyrus and characterized by flow cytometry, showed a reduced proportion of NSCs and an increased proportion of neuroblasts—neuronal committed progenitors—in Fmr1-KO mice. Together, these results indicate that hippocampal NPCs show aberrant proliferation and neurogenesis during early postnatal development. This could indicate stem-cell depletion, increased quiescence, or a developmental delay in relation to lack of FMRP and uncovers a new role for FMRP in the early postnatal hippocampus. In turn, elucidating the mechanisms that underlie FXS will aid in the development of targeted treatments. / Thesis / Doctor of Philosophy (PhD) / Fragile X syndrome is the leading inherited cause of intellectual impairment and autism spectrum disorder. The syndrome is caused by a defect in one gene. This gene has been suggested to play a role in regulating the birth of new brain cells termed neural precursor cells. The importance of neural precursor cells stems from their ability to generate neurons and glia, the main cells in the brain. In this thesis, I focus on studying neural precursor cells from the hippocampus, a brain region important for learning and memory. A mouse model was used to compare neural precursor cells from healthy and Fragile X mice during early postnatal development. I found that neural precursor cells do not divide as much as they should in the Fragile X mouse hippocampus. The results help to determine the causes for learning and memory deficits in Fragile X and potentially open avenues for intervention.

No description available.

by Zhao Zheng. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references (leaves 87-98). / Acknowledgements --- p.i / Abstract --- p.ii / List of Tables --- p.iii / List of Figures --- p.iv / Chapter Chapter 1 --- Introduction --- p.i / Chapter 1.1 --- History --- p.1 / Chapter 1.2 --- Chromosomal Fragile Sites --- p.2 / Chapter 1.3 --- Cytogenetics of the Fragile Site at Xq27.3 --- p.3 / Chapter 1.4 --- Clinical Findings in Fragile X --- p.5 / Chapter 1.5 --- Prevalence --- p.6 / Chapter 1.6 --- The Mode of Inheritance and the Sherman Paradox --- p.8 / Chapter 1.7 --- Molecular Genetics of the FMR-1 Gene --- p.11 / Chapter 1.7.1 --- The Mutation Locus and Linkage Analysis --- p.11 / Chapter 1.7.2 --- Abnormal DNA Methylation in the CpG Island --- p.12 / Chapter 1.7.3 --- Isolation of the FMR-1 Gene --- p.13 / Chapter 1.7.4 --- CGG Trinucleotide Repeats in FMR-1 --- p.13 / Chapter 1.7.5 --- DNA Instability and Mutational Mechanisms --- p.17 / Chapter 1.7.6 --- Gene Expression --- p.18 / Chapter 1.7.7 --- Resolution of the Sherman Paradox --- p.19 / Chapter 1.8 --- Methods of Detection for the Fragile X Mutation --- p.20 / Chapter 1.8.1 --- Cytogenetic Analysis --- p.20 / Chapter 1.8.2 --- Diagnosis by Direct DNA Analysis --- p.21 / Chapter 1.8.2.1 --- Southern Blot Analysis --- p.22 / Chapter 1.8.2.2 --- PCR Analysis --- p.27 / Chapter 1.9 --- Studies of the Fragile X Syndrome in Mainland China --- p.29 / Chapter Chapter 2 --- Objectives of the Project --- p.33 / Chapter Chapter 3 --- Materials and Methods --- p.34 / Chapter 3.1 --- Chemical Materials --- p.34 / Chapter 3.1.1 --- Enzymes --- p.34 / Chapter 3.1.2 --- DNA Markers --- p.34 / Chapter 3.1.3 --- Reagent Kits --- p.34 / Chapter 3.1.4 --- Primers for Polymerase Chain Reaction --- p.35 / Chapter 3.1.5 --- Chemical Reagents --- p.35 / Chapter 3.1.6 --- Nylon Membranes --- p.36 / Chapter 3.1.7 --- Radioisotopes --- p.36 / Chapter 3.1.8 --- Buffers and Solutions --- p.36 / Chapter 3.2 --- Clinical Materials --- p.38 / Chapter 3.2.1 --- Control Subjects --- p.38 / Chapter 3.2.2 --- Fragile X Patients --- p.39 / Chapter 3.2.3 --- Mentally Retarded Patients --- p.39 / Chapter 3.3 --- Methods --- p.40 / Chapter 3.3.1 --- Blood Collection --- p.40 / Chapter 3.3.2 --- DNA Isolation --- p.43 / Chapter 3.3.2.1 --- The Salting-out Method --- p.43 / Chapter 3.3.2.2 --- DNA Quantitation --- p.44 / Chapter 3.3.3 --- Labelling of StB12.3 Probe by [α-32P]-dCTP --- p.44 / Chapter 3.3.3.1 --- The Random Priming Method --- p.44 / Chapter 3.3.3.2 --- Purification of Radioactive StB12.3 Probe --- p.45 / Chapter 3.3.3.3 --- Assessment of [α-32P] Incorporation in StB12.3 --- p.45 / Chapter 3.3.4 --- Southern Blot Analysis --- p.46 / Chapter 3.3.4.1 --- Preparation of DNA Fragments --- p.46 / Chapter 3.3.4.2 --- Blotting by Capillary Action --- p.46 / Chapter 3.3.4.3 --- Southern Hybridization --- p.47 / Chapter 3.3.5 --- PCR Amplification and Detection of PCR Products --- p.48 / Chapter 3.3.5.1 --- PCR Amplification --- p.48 / Chapter 3.3.5.2 --- Labelling of (CGG)5 Probe and HpaII Digested pBR322 DNA Marker --- p.49 / Chapter 3.3.5.3 --- Detection of the PCR Products --- p.50 / Chapter Chapter 4 --- Results --- p.52 / Chapter 4.1 --- Amplification of the FMR-1 Gene --- p.52 / Chapter 4.2 --- Analysis of the FRAXA Site by Southern Hybridization --- p.52 / Chapter 4.3 --- Distribution of CGG Repeat Sizes in Normal Unrelated Chinese Subjects in Hong Kong --- p.55 / Chapter 4.4 --- Comparison of CGG Repeat Patterns Among Normal Subjects from Different Parts of China --- p.61 / Chapter 4.5 --- CGG Repeat Pattern in Mildly Mentally Retarded Children in Hong Kong --- p.65 / Chapter 4.6 --- Investigation of Suspected Fragile X Families --- p.69 / Chapter Chapter 5 --- Discussions --- p.73 / Chapter 5.1 --- Distribution of CGG Repeats in Normal Chinese Population --- p.73 / Chapter 5.2 --- Overlap Between the Normal and Premutation Alleles --- p.78 / Chapter 5.3 --- CGG Allele Distribution in Mildly MR Patients --- p.79 / Chapter 5.4 --- Molecular Analysis of Fragile X Syndrome Families --- p.80 / Chapter 5.5 --- Somatic Instability of CGG Repeats --- p.82 / Chapter Chapter 6 --- Conclusions --- p.85 / Bibliography --- p.87

Les vibrisses ou moustaches, sont représentées de façon très précise au niveau cortical. Cette représentation forme une carte qui peut varier selon l’expérience ou l’apprentissage. La plasticité corticale est parfois altérée dans des maladies. C’est le cas du syndrome de l’X-fragile où la protéine FMRP n’est plus produite. Notre hypothèse est double : 1- La plasticité opérant dans le cortex somato-sensoriel primaire lors d’un conditionnement associatif est primordiale pour l’apprentissage. 2- FMRP peut perturber cette plasticité et altérer l’acquisition de la mémoire. Mon travail de thèse s’est déroulé sous la direction du Dr Ingrid Bureau, dans l’Institut de neurobiologie de la Méditerranée UMR901, laboratoire de l’INSERM, sur le campus universitaire de Luminy (Aix-Marseille Université).Après un protocole de conditionnement, les souris ayant appris l’association présentent des réorganisations de la carte corticale sélective manifestées par une surreprésentation des vibrisses appariées au dépend des vibrisses voisines.L’étude a ensuite montré que déjà en condition naïve l’excitabilité des neurones glutamatergiques de la couche 4 est plus importante que chez les souris mutantes, dans lequel la synthèse de FMRP n’est inactivée que dans la couche 4 du cortex somato-sensoriel. Ceci est couplé à une baisse de la probabilité de libération de neurotransmetteur et une baisse de connectivité. Les cartes corticales sauvages et mutantes en condition naïve sont donc en apparence similaires. Après altération de l’expérience sensorielle, nous avons observé une forte augmentation de la force des projections ascendantes de la couche 4 vers la couche 2/3 chez les individus mutants / Whiskers representation is well defined at cortical level. This representation designs a map which can be modified with sensory experiece or learning. Cortical plasticity is sometime affected by diseases such as the fragile-X syndrome where protein FMRP is lacking. Two hypothesis : 1- Plasticity in primary somatosensory cortex play a major role in learning. 2- FMRP can disturb that plasticity and so memory acquisition.After playing an associtiative conditionning protocol, some mice learn the association and cortical map changes in a selective way with a gain of representation for the paired whiskers vs whiskers in neighbourghood.We’ve after shown that in naive conditions, layer 4 glutamatergic neurons present an increase of excitability in mutant mice, in which FMRP synthesis is inactivated only in layer 4 of somatosensory cortex. This phenotype comes with a decrease in neurotransmetor release probability and a decrease in connectivity. This way, WT and mutant cortical maps appear similar in naive conditions. But after sensory alteration we’ve seen a huge increase in strenght of ascending projections from layer 4 to layer 2/3 in mutants. We don’t know yet how to explain thoose deregulations.

<p> Fragile X Syndrome (FXS) is the most common inherited disease of mental impairment, typically caused by a mutation in the Fragile X mental retardation 1 (FMRJ) gene. The clinical features are thought to result from abnormal neurobiology due to a lack of the Fragile X mental retardation protein (FMRP). Previously, it was thought that FMRP was confined exclusively to neurons; however, our laboratory recently discovered that astrocytes also express FMRP. Consequently, it is possible that astrocytes also suffer abnormalities as a result of a lack of FMRP. Astrocytes play integral roles in the development and maintenance of communication in the central nervous system. Therefore, it is now important to determine the contribution of astrocytes to the abnormal neuronal phenotype seen in FXS. In these experiments, neurons and astrocytes were independently isolated from wild type (WT) or FMRJ null mice and grown in a coculture. Neurons were evaluated using immunocytochemistry in combination with computer-aided morphometric and synaptic protein analyses. The findings presented here provide convincing evidence that Fragile X astrocytes contribute to the abnormal neurobiology seen in FXS . Fragile X astrocytes alter the dendrite morphology and excitatory synaptic protein expression of WT neurons in culture; and, importantly, when Fragile X neurons are grown with WT astrocytes these changes are prevented. Interestingly, the Fragile X astrocytes appear to act by causing a delay in development; even WT neurons grown in the presence of Fragile X astrocytes, that displayed an abnormal phenotype at 7 days in culture, exhibited nearly normal dendrite morphology and expression of excitatory synapses at 21 days. Furthermore, the results suggest that the dendritic abnormalities induced by the Fragile X astrocytes specifically target neurons with a spiny stellate morphology. This research establishes a role for astrocytes in the development of the abnormal neurobiology seen in FXS, and as such, the results presented here have significant implications for Fragile X research. The novel prospect that astrocytes are key contributing components in the development of FXS provides an exciting new direction for investigations into the mechanisms underlying FXS, with many unexplored avenues for potential treatment strategies. </p> / Thesis / Doctor of Philosophy (PhD)

Résumé: Mémoire présenté à la Faculté de médecine et des sciences de la santé en vue de l’obtention du diplôme de maître sciences (M.Sc.) en biochimie, Faculté de médecine et des sciences de la santé, Université de Sherbrooke, Sherbrooke, Québec, Canada, J1H 5N4. Le document présent est un mémoire par article, lequel explorera la fonction d'une protéine liant l'ARN, FMRP, dans la différenciation cellulaire. Cette protéine joue un rôle de premier plan puisque son absence conduit à des anomalies développementales durant la neurogenèse et à une plasticité synaptique déficiente. Ces anomalies sont observées chez la souris KO pour le gène FMR1, mais également dans le cerveau des individus avec le syndrome du X fragile (SXF). Ces derniers dont le gène FMR1 est muté présentent une déficience intellectuelle (DI). Puisque la DI est la principale manifestation du SXF, et que les neurones « normaux » expriment FMRP à des niveaux supérieures à ceux des autres tissus corporels, son rôle a presqu'exclusivement été étudié dans les cellules neuronales. Pourtant, FMRP est une protéine hautement conservée et est exprimée dans presque toutes les cellules du corps. Logiquement, FMRP devrait jouer un rôle important dans tous les tissus l’exprimant à des niveaux de base, bien que son absence dans les tissus ne se manifeste pas cliniquement. Cette polyvalence fonctionnelle est encore plus probable de par le fait que plusieurs ARNm différents ont la possibilité d’interagir avec FMRP puisqu’elle identifie ses cibles par reconnaissance de motifs. L'étude présentée se fonde sur l'hypothèse que FMRP effectue des fonctions de base critiques au développement de tous types de tissus humains, et non seulement dans les neurones. L’hypothèse sera davantage développée. Puis, un modèle innovateur de la différenciation cellulaire non-neuronal sera présenté pour l'étude de FMRP. L'enquête sur la distribution subcellulaire et les interactions dynamiques de cette protéine sera détaillée durant les différents changements morphologiques de la spécialisation et de la maturation cellulaire. Les résultats des expériences seront analysés en profondeur. Puis, un retour sur l'hypothèse en guise des résultats expérimentaux permettra de constater que FMRP semble bien jouer un rôle durant la différenciation cellulaire non-neuronale. Ce rôle est intimement lié à la réorganisation du cytosquelette et à la synthèse protéique locale, régulée dans les complexes mRNPs composés de FMRP et ses cibles d'ARNm qui sont régulés, stabilisés et transportés vers les régions en maturation. Ultimement, plusieurs éléments indiquent que FMRP doit interagir correctement avec de nombreuses molécules, décrites dans ce mémoire, afin de permettre aux cellules de se spécialiser et d'acquérir les caractéristiques désirées au cours d’une différenciation normale. / Abstract: The present article-based memoire will explore the involvement of an important RNA-binding protein, FMRP, in cellular differentiation. This protein is well-known for the developmental anomalies during neurogenesis as well as the loss of synaptic plasticity which occur when its gene, FMR1, is mutated. Since FMRP expression is most pronounced in neurons and because the absence of its expression results in the intellectual deficiency known as the Fragile X Syndrome, FMRP has nearly always been studied in neurons alone. However, FM RP is a highly conserved protein, expressed ubiquitously across the body. Additionally, its influence in cells can be vast since its motif - based RNA recognition renders it capable of binding a variety of transcripts. Logically speaking, FMRP should play a role of first rate importance in the other tissues where it is present. The clinical manifestation of its impact in those tissues is likely to be lessened only by the lower levels of FMRP expressed in the average human cell. The main hypothesis of the current study is that FMRP performs critical but basic functions involved in the development of all human tissues where it is present at basal levels, rather than exerting an impact limited to the nervous system alone. The hypothesis will be further elaborated. An innovative non-neuronal model will be presented for the study of FMRP throughout the differentiation process. The behaviour and dynamic interactions of FMRP during cell specialization and morphological maturation will be investigated. An in-depth analysis of the experimental results will follow. Returning to the hypothesis of the study with these results at hand, it will be concluded that FMRP does indeed appear to play a major role in the differentiation of non-neuronal cells. In fact, FMRP's function seems to be closely linked to cytoskeletal reorganization, as well as local protein synthesis through the formation of mRNP complexes with its target mRNAs, which are stabilized, regulated and transported towards the active areas of the cell in differentiation. Ultimately, it is clear that proper interaction between FMRP and certain types of molecules, described in this memoire, is required for cells to specialize and acquire the characteristics of mature cells through normal differentiation.

The prevalence of Autism Spectrum Disorder (ASD) and its defining features has been increasingly investigated in genetic syndromes associated with intellectual disability, with syndrome specific profiles reported. The experience of catatonia and other movement disorders in people with ASD has been increasing highlighted within both research and diagnostic guidelines. However, these issues have not typically been investigated alongside other features of ASD within research into genetic syndromes. The first paper in this thesis provides a review of the literature on movement disorders in genetic syndromes associated with ASD, which focuses on the prevalence of reported movement disorders, the methods of assessment used, and the quality of research to date. An empirical study is reported in Paper 2. Within a cohort of individuals with Cornelia de Lange and Fragile X syndromes the prevalence of attenuated behaviour [autistic catatonia] is examined, based on parent/carer report, and the extent to which features of ASD predict later attenuated behaviour is investigated. Paper 3 provides a critical reflection on the first two papers as well as some wider considerations on undertaking research in this area. The results of both the literature review and the empirical study indicated that across a number of genetic syndromes (Angelman syndrome, Cornelia de Lange syndrome, Fragile X syndrome and Rett syndrome) attenuated behaviour [autistic catatonia] and/or movement disorders affect a substantial proportion of individuals. Furthermore, repetitive behaviours, one of the characteristic features of ASD, appear to predict later attenuated behaviour in Cornelia de Lange and Fragile X syndromesThe results presented in this thesis have important implications for the way services support individuals with specific genetic syndromes. Paper 1 confirms the high prevalence of movement problems in Angelman and Rett syndromes, and Paper 2 provides a new insight into movement problems in Cornelia de Lange and Fragile X syndromes. Movement disorders are reported to impact negatively on wellbeing and quality of life in people with ASD, and are likely to have a similar impact on the lives of people with genetic syndromes. Greater awareness and recognition of movement problems in CdLS and FXS is required, and although specialist services may already be aware of some of the above issues, there should be an increased emphasis on ensuring that community services are aware of the needs of individuals with genetic syndromes, including the implications of movement problems for support needs and quality of life.

Angelman Syndrome (AS) is a severe neurodevelopmental disorder that affects 1:12000 newborns. It is characterized by mental retardation, delayed major motor and cognitive milestones, seizures, absence of speech and excessive laughter. The majority of AS cases arise from deletions or mutations of UBE3A gene located on the chromosome 15q11-13. UBE3A codes for E3-ubiquitin ligase that target specific proteins for degradation. To date, a wide variety of Ube3a substrates has been identified. The accumulation of Ube3a-dependent proteins and their effect on the multitude of signal transduction pathways are` considered the main cause of the AS pathology. While the majority of research has been directed towards target identifications, the overall role of Ube3a in activity-dependent synaptic plasticity has been greatly overlooked. The present work is designed to fill some of these knowledge gaps. Chapter 2 is focused on the activity-dependent aspect of Ube3a expression following neuronal stimulation in vivo and in vitro. We examined total Ube3a expression followed by KCl depolarization in neuronal primary culture. By utilizing a subcellular fractionation technique, we were able to determine which cellular pools are responsive to the depolarization. Next, a fear conditioning paradigm (FC) was used to activate neurons in the paternal Ube3a-YFP reporter mouse brain. This mouse model allowed us to resolve spatial and temporal alterations of the maternal and the paternal Ube3a in hippocampus and cortex followed by FC. In accordance to KCl depolarization results, we observed alterations in Ube3a protein but at later time points. Furthermore, we investigated if the absence of activity-dependent Ube3a changes has any effect on learning and memory kinase activation. We utilized KCl and FC to determine synaptic activity-induced ERK 1/2 phosphorylation in acute hippocampal slices and in CA1 area of hippocampus of wild type (Ube3a m+/p+) and Ube3a deficient mice (Ube3a m-/p+). We demonstrated that Ube3a loss leads to impaired activity-dependent ERK 1/2 phosphorylation. It has been established that Ube3a m-/p+ mice have a profound deficit in LTP, implying the importance of this ligase in excitatory synaptic transmission. The abnormal LTP could be partially explained by an aberrant CaMKII function, decreased activity-dependent ERK 1/2 phosphorylation and reduced phosphatase activity. These proteins have also been implicated in another form of synaptic plasticity such as long-term depression (LTD). Chapter 3, we investigated the contribution of Ube3a to NMDAR - dependent and - independent LTD. Our data showed that Ube3a m-/p+ P21-30 animals exhibit the impairments in both forms of LTD. Next, we focused on elucidating molecular mechanism underlying the reduced mGluR1/5-LTD. We discovered that mGluR1/5 kinase activation such as ERK, mTOR and p38 is not affected by Ube3a loss. In concordance with previous work, we detected increased Arc expression together with abnormal AMPAR distribution in the Ube3a m-/p+ hippocampus. Surprisingly, the mGluR1/5 induced GluR2 trafficking was normal. Our findings infer that elevated Arc levels together with the increased internalization of AMPAR may result in compromised basal state of the synapses leading to a more depression-like state in Ube3a m-/p+ mice. Evidence points that loss of Ube3a produces alterations in a variety of activity-dependent signal transduction cascades that may ultimately result in impaired synaptic plasticity and cognition. Similar to AS, abnormal molecular and behavioral phenotypes have already been observed in other mouse models of human mental retardation such as Fragile X Mental Retardation Syndrome (FXS). Chapter 4 is set to explore if any correlation can be found in between these neurodevelopmental disorders. Analysis of crude synaptoneurosomes of adult Fmr1 KO mice revealed a significant reduction in Ube3a protein. Additionally, a blunted translation of Ube3a in response to mGluR1/5 stimulation was observed. However, we didn't find any evidence of direct interaction between Ube3a mRNA and Fragile X Mental Retardation Protein (FMRP). To examine if some of the pathology seen in Fmr1 KO mice is due to Ube3a downregulation, we performed a rescue experiment by increasing overall levels of Ube3a in hippocampus of FRMP deficient mice. An exhaustive battery of behavioral testing indicated that alterations of Ube3a expression impacted only associative fear conditioning. In summary, the present work has attempted to answer some of the fundamental questions about Ube3a and its role in synaptic plasticity. We have demonstrated that Ube3a expression is modulated by synaptic activation and its activity-dependent alterations are essential for normal brain functioning. Additionally, our data suggest that Ube3a is not only significant for the synaptic excitation but also crucial for the synaptic depression. Finally, our findings indicate that the alteration of Ube3a expression may contribute to the cognitive phenotypes in other neurodevelopmental disorders such as FXS suggesting an advantage of exploring Ube3a function outside the AS research.

Raising a child with a pervasive developmental disorder (PDD), particularly that of Fragile X Syndrome (FXS), is challenging, as it comes with parental stressors for both mothers and fathers. Research on these stressors has been limited to only the stressors that mothers of children with a PDD experience and has failed to thoroughly examine the experiences and stressors of fathers of children with a PDD, particularly that of FXS. Using Hill's ABC-X family stress theory, this quantitative research study investigated the effects of marital satisfaction due to the amount of shared childcare responsibilities and parental stress among the mothers and fathers of children diagnosed with FXS. This study also examined whether significant differences exist among these parents, who were recruited through the use of flyers, notices, and handouts that were randomly passed out to parents at the FXS Alliance of Texas located in the southwest region of Texas. Participants for this study were 128 parents of children with FXS, each of whom completed a demographic questionnaire, the Kansas Marital Satisfaction Scale, and The Sharing of Childcare Responsibilities Scale and Parental Stress Level Scale. An independent samples t test and multiple linear regression statistical analysis was employed. The results of the study indicated that parental stress associated with the amount of shared childcare responsibilities accounted for a significant degree of the variance in marital satisfaction. Yet the study did not find a significant mean difference in the level of parental stress that was experienced uniquely across gender. Potential social changes may include future development and improvements in treatment, therapeutic approaches, and predicted outcomes in efforts to enhance parental stress interventions so as to improve stress-related outcomes for parents of children with FXS.

The purposes of this qualitative inquiry were as follows: (a) to understand how mothers of children with fragile X syndrome (FXS) used augmentative and alternative communication (AAC) systems in the home, (b) to capture their views regarding AAC use, and (c) to examine the support they received in the process. Data was collected using participant observations, semi-structured interviews and review of archival educational records and were analyzed using grounded theory methods. Results revealed that for children with FXS, the interplay of children’s complex developmental challenges, mothers’ internal struggles, and the absence of external supports leads to limited and variable use of AAC in the home.